Okavango River Basin Technical
Diagnostic Analysis:
Environmental Flow Module
Specialist Report
Country: Botswana
Discipline: Fish
K. Mosepele
June 2009

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EFA Botswana Fish






Okavango River Basin Technical
Diagnostic Analysis:
Environmental Flow Module



Specialist Report

Country: Botswana

Discipline: Fish

Author: K. Mosepele

Date: June, 2009


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EFA Botswana Fish



EXECUTIVE SUMMARY
This EFA was done using existing fisheries data from the Delta and literature from various
sources. The data used in this study was collected from two rapid assessments fo the Delta's
fishery at low and high flood periods. Another data set used is based on an ongoing long
term monitoring of the Delta' fishery from three sites in the Delta's panhandle, one site in the
lower delta around Chief's island, one site in Moremi at Xakanaxa and three sites in the
Boteti River. These experiemental fishing data were/ are collected using various fishing gear
such as seine nets, two main kinds of research nets (mono-filament, nylon multi-panel nets;
multi-filament, cotton, multi-panel nets). Furthermore, several studies have also been done
on the socio-economic value of the fishery to the Delta's communities. All these data,
biological/ ecological and socio-economic data, then form the basis for the formulation of a
fisheries management plan for the Okavango Delta that is currently ongoing. Most of the
literature used in this study was based on comprehensive research done on the ecology/
biology of the Delta's fishery in the early 1980's. It was on the basis of these literature (and
data) sources that six fish guilds were developed for the Okavango Delta to use them as
indicators for this EFA.

The major findings made in this study indicate that the Delta's seasonal flood pulse is the
major driver of ecological/ biological change in the Delta's fish populations. The timing of
migrations for breeding and feeding, the timing for actual spawning and generally most of the
life history strategies of the Delta's fish species are controlled by the flood regime. The best
example of these is the annual catfish run in the Delta which occurs annualy between August
and October where catfish (especially Clarias gariepinus and C. ngamensis) form hunting
packs that migrate slowly downstream and feed voraciously on Marcusenius macrolepidotus
that are back-migrating into the main channel from the slowly drying out floodplains. Another
major result observed is the seasonal changes in feeding ecology of most fish species where
their diet varies between terrestrial and aquatic food sources depending on the flood regime.
This suggests that at certain times of the year, there is direct energy flow into the fish
community from terrestrial sources that are trapped by the newly arrived floods. A good
example of this observation is the high proportion of termites in the diet of Schilbe
intermedius when the floods arrive in the lower Delta. Another major observation is that due
to the nature of the Delta, with its high inter and intra variability, the Delta's fish species are
generally resilient to changes in the hydrological regime as long as they fall within the natural
variations. This based on the observation of some species that mouthbrood their eggs (such
as Oreochromis andersonii, etc)which enhances the survial of their young even under
adverse conditions. Species such as Hepsetus odoe make oxygen enriched bubble nests
where they lay their eggs and this protects the eggs from low oxygen conditiosn that may be
caused by variations in the flow regime. Other species such as the catfishes (especially the
Clarias group) have vestigial lungs that enbale them to breathe atmospheric oxygen when
also helps them to survive under adverse conditions.

Expert knowledge was used to produce response curves on how these indicator species
would react to variations in the Delta's flow regime caused by water development under
several scenarios. This knowledge was a consolidation of ideas from experts from Angola,
Botswana and Namibia which was then used to develop the response curves. As expected,
minor decreases were observed in fish abundance caused by low and medium water
development scenarios in the Basin. However, a high water development scenario showed
that there will sharp decreases in fish abundance at the three study sites in Botswana, with
the most darstic changes occuring in the Boteti River. While these results were expected
based on the information available, there were gaps in knowledge which resulted in a low
confidence in some of the results obtained. Clearly, the knowledge that exists in the



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EFA Botswana Fish

Okavango Delta allows for a preliminary study of this nature, but there is need to conduct
more directed research to ioncrease the confidence of some of the osbervations and hence
better prediction models based on the various water development scenarios. Furthermore, it
is understood that this prediction model is preliminary on account of the fact that it does not
yet inlcude aspects of climate change in it. Certainly incorporating climate change effects into
this prediction model may highten the anticipated effects of these development scenarios on
fish stocks in the Okavango Delta, and indeed in the entire basin. Nonetheless, the model
worked as expected and the results it produced were plausible, which indicates that the
model is appropriate for this kind of dynamic and complex system.





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EFA Botswana Fish

TABLE OF CONTENTS

EXECUTIVE SUMMARY .......................................................................................................... 3
LIST OF TABLES ..................................................................................................................... 7
LIST OF FIGURES ................................................................................................................... 7
ACKNOWLEDGEMENTS ........................................................................................................ 8
INTRODUCTION ...................................................................................................................... 9
1.1 Background ................................................................................................... 9
1.2 Okavango River Basin EFA Objectives and Workplan .................................. 9
1.2.1 Project objectives .................................................................................... 9
1.3 Layout of this report ..................................................................................... 10
STUDY AREA ........................................................................................................................ 10
1.1 Description of the Okavango Basin ............................................................. 10
1.2 Delineation of the Okavango Basin into Integrated Units of Analysis .......... 11
IDENTIFICATION OF INDICATORS AND FLOW CATEGORIES ......................................... 12
1.1 Indicators ..................................................................................................... 12
1.1.1 Introduction ........................................................................................... 12
1.1.2 Indicator list for Fish .............................................................................. 13
1.1.3 Description and location of indicators ................................................... 13
1.2 Flow categories ­ river sites ........................................................................ 16
1.1 Inundation categories ­ delta sites .............................................................. 19
LITERATURE REVIEW .......................................................................................................... 20
1.1 Indicator 1: Main channel/ open water species ............................................ 23
1.1.1 Main characteristics of Indicator 1 ......................................................... 23
1.1.2 Life cycle attributes of Indicator 1 .......................................................... 23
1.1.3 Links to flow .......................................................................................... 23
1.1 Indicator 2: Small species that undertake lateral migrations into the shallow,
seasonally flooded floodplains .............................................................................. 25
1.1.1 Main characteristics of Indicator 2 ......................................................... 25
1.1.2 Life cycle attributes of Indicator 2 .......................................................... 26
1.1.3 Links to flow .......................................................................................... 26
1.2 Indicator 3: Large species that undertake lateral migrations into the shallow,
seasonally flooded floodplains .............................................................................. 26
1.3 Main characteristics of Indicator 3 ............................................................... 26
1.3.1 Life cycle attributes of Indicator 3 .......................................................... 27
1.3.2 Links to flow .......................................................................................... 27
1.4 Indicator 4: marginal vegetation dwellers of the main channel and floodplain
lagoons ................................................................................................................. 28
1.4.1 Main characteristics of Indicator 4 ......................................................... 28



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EFA Botswana Fish

1.4.2 Life cycle attributes of Indicator 4 .......................................................... 29
1.4.3 Links to flow .......................................................................................... 29
1.5 Indicator 5: sandbank specialists: Species that prefer clear, slow flowing or
quiet well vegetated water in the main channel ..................................................... 29
1.5.1 Main characteristics of Indicator 5 ......................................................... 29
1.5.2 Life cycle attributes of Indicator 5 .......................................................... 29
1.5.3 Links to flow .......................................................................................... 29
1.6 Indicator 6: Shallow, well vegetated backwater habitats .............................. 30
1.6.1 Main characteristics of Indicator 6 ......................................................... 30
1.6.2 Life cycle attributes of Indicator 6 .......................................................... 30
1.6.3 Links to flow .......................................................................................... 30
1.7 Summary ..................................................................................................... 30
DATA COLLECTION AND ANALYSIS ................................................................................... 31
1.8 Methods for data collection and analysis ..................................................... 31
1.9 Results ........................................................................................................ 31
1.10
A summary of present understanding of the predicted responses of all fish
indicators to potential changes in the flow regime ................................................. 31
5 DATA COLLECTION AND ANALYSIS ........................................................... 32
Methods for data collection and analysis .............................................................. 32
A summary of present understanding of the predicted responses of all bird
indicators to potential changes in the flow regime ................................................. 32
4.11.1 Fish Indicator 1 ­ Resident in river ......................................................... 33
4.11.2 Fish Indicator 2 ­ Small fish migrating to floodplains .............................. 34
4.12 Conclusion ............................................................................................... 39
5 FLOW-RESPONSE RELATIONSHIPS FOR USE IN THE OKAVANGO EF-DSS.............. 40
6REFERENCES ..................................................................................................................... 40
APPENDIX A: FULL DESCRIPTIONS OF INDICATORS ...................................................... 44






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EFA Botswana Fish

LIST OF TABLES
Table 2.1 Location of the eight EFA sites ................................................................... 12
Table 3.1 List of indicators for fish and those chosen to represent each site ............. 13
Table 3.2 Questions to be addressed at the Knowledge Capture Workshop, per
indicator per site. In all cases, `natural' embraces the full range of
natural variability ...................................................................... 19
Table 3.3 Inundation categories for the Okavango Delta as recognised by the HOORC
inundation model ...................................................................... 20
Table 0.1 Predicted response to possible changes in the flow regime of fish resident in
river in the Okavango River ecosystem .................................... 33



LIST OF FIGURES
Figure 2.1 Upper Okavango River Basin from sources to the northern end of the Delta10
Figure 2.2 The Okavango River Basin, showing drainage into the Okavango Delta and
the Makgadikgadi Pans ............................................................ 11
Figure 3.1 Three representative years for Site 1: Cuebe River @ Capico, illustrating the
approximate division of the flow regime into four flow seasons 17
Figure 3.2 Three representative years for Site 2: Cubango River @ Mucindi, illustrating
the approximate division of the flow regime into four flow seasons
................................................................................................. 17
Figure 3.3 Three representative years for Site 3 Cuito River @ Cuito Cuanavale,
illustrating the approximate division of the flow regime into four
flow seasons ............................................................................ 18
Figure 3.4 Three representative years for Site 4: Okavango River @ Kapoka
(hydrological data from Rundu), illustrating the approximate
division of the flow regime into four flow seasons .................... 18
Figure 3.5 Three representative years for Site 5: Okavango River @ Popa (hydrological
data from Mukwe), illustrating the approximate division of the flow
regime into four flow seasons ................................................... 19




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EFA Botswana Fish


ABBREVIATIONS

ABBREVIATION
MEANING
DTM
Digital Terrain Model
HOORC
Harry Oppenheimer Okavango Research Centre

ACKNOWLEDGEMENTS
The major part of this work involved intensive literature research from the library and great
appreciation is extended to the HOORC library staff who really went out of their way to assist
me. Specifically, I wish to extend my greatest gratitude to Ms Monica Morrison who was
always so ready and helpful whenever I need material from the HOORC library. Mrs. Daisy
Mafanetsa was always ready and willing to assist me with literature needs and she dealt with
inter-library loans on my behalf and did some photo-copying. Thank you all for your kind
assistance. I also wish to extend my warmest regards to my two colleagues from Angola (Mr
M. Morais) and Namibia (Dr. B. van der Waal) who were always ready to share their
knowledge and expertise with me.







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EFA Botswana Fish

INTRODUCTION
1.1 Background
An Environmental Protection and Sustainable Management of the Okavango River Basin
(EPSMO) Project is being implemented under the auspices of the Food and Agriculture
Organization of the United Nations (UN-FAO). One of the activities is to complete a
transboundary diagnostic assessment (TDA) for the purpose of developing a Strategic Action
Plan for the basin. The TDA is an analysis of current and future possible causes of
transboundary issues between the three countries of the basin: Angola, Namibia and
Botswana. The Okavango Basin Steering Committee (OBSC) of the Okavango River Basin
Water Commission (OKACOM) noted during a March 2008 meeting in Windhoek, Namibia,
that future transboundary issues within the Okavango River basin are likely to occur due to
developments that would modify flow regimes. The OBSC also noted that there was
inadequate information about the physico-chemical, ecological and socioeconomic effects of
such possible developments. OBSC recommended at this meeting that an Environmental
Flow Assessment (EFA) be carried out to predict possible development-driven changes in
the flow regime of the Okavango River system, the related ecosystem changes, and the
consequent impacts on people using the river's resources.

The EFA is a joint project of EPSMO and the Biokavango Project. One part of the EFA is a
series of country-specific specialist studies, of which this is the Fish Report for Botswana

1.2
Okavango River Basin EFA Objectives and Workplan
1.2.1 Project
objectives
The goals of the EFA are:
To summarise all relevant information on the Okavango River system and its users, and
collect new data as appropriate within the constraints of the EFA
to use these to provide scenarios of possible development pathways into the future for
consideration by decision makers, enabling them to discuss and negotiate on sustainable
development of the Okavango River Basin;
to include in each scenario the major positive and negative ecological, resource-economic
and social impacts of the relevant developments;
to complete this suite of activities as a pilot EFA, due to time constraints, as input to the TDA
and to a future comprehensive EFA.

The specific objectives are:
to ascertain at different points along the Okavango River system, including the Delta, the
existing relationships between the flow regime and the ecological nature and functioning of
the river ecosystem;
to ascertain the existing relationships between the river ecosystem and peoples' livelihoods;
to predict possible development-driven changes to the flow regime and thus to the river
ecosystem;
to predict the impacts of such river ecosystem changes on people's livelihoods.
To use the EFA outputs to enhance biodiversity management of the Delta.
To develop skills for conducting EFAs in Angola, Botswana, and Namibia.




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EFA Botswana Fish

1.3
Layout of this report
Chapter 1 gives an introduction of this study/ project followed by Chapter 2 which provides a
description of the study area. Chapter 3 then outlines the fish indicators developed in this
study which are then discussed in detail in a literature review given in Chapter 4. Chapter 5
summarizes predicted responses of the indicators to various flooding scenarios, Chapter 6
lists references used in this report while Appendix A gives a full description of the indicators
used in the report.

STUDY AREA
1.1
Description of the Okavango Basin
The Okavango River Basin consists of the areas drained by the Cubango, Cutato, Cuchi,
Cuelei, Cuebe, and Cuito rivers in Angola, the Okavango River in Namibia and Botswana,
and the Okavango Delta (Figure 0.1). This basin topographically includes the area that was
drained by the now fossil Omatako River in Namibia. Outflows from the Okavango Delta are
drained through the Thamalakane and then Boteti Rivers, the latter eventually joining the
Makgadikgadi Pans. The Nata River, which drains the western part of Zimbabwe, also joins
the Makgadikgadi Pans. On the basis of topography, the Okavango River Basin thus
includes the Makgadikgadi Pans and Nata River Basin (Figure 0.2). This study, however,
focuses on the parts of the basin in Angola and Namibia, and the Panhandle/Delta/Boteti
River complex in Botswana. The Makgadikgadi Pans and Nata River are not included.
Upper Okavango River Basin
N
W
E
S
C
u
tato
Cu
#
c
h
i
#
C
C
u
u
#
it
a
o
nava
#
le
Cu
#
C
Menongue
ba
u
n
c
g
h
#
Major settlement
o
i
# Cuito Cuanavale
River
C
#
ue
Fossil river
be
C
Panhandle
ANGOLA
uiri
Permanent swamps
ri
#
Seasonal swamps
Cubango
Cuito
NAMIBIA
Okavango
#
Rundu
#
#
#
0
300 Kilometers
#

Figure 0.1 Upper Okavango River Basin from sources to the northern end of the Delta


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EFA Botswana Fish

Okavango River Basin
N
W
E
S
C
u
ta
Cu
#
to
c
hi
#
C
C
ui
ua
#
t
o
nava
#
l
e
C
# Menongue
ub
C
a
u
n
c
g
h
o
i
# Cuito Cuanavale
# Cuebe
C
ANGOLA
uirir
#
i
Cubango
Cuito
NAMIBIA
Okavango
#
Rundu
#
# #
#
##
#
#
#
Maun
#
Makgadikgadi Pans
# Ghanzi
#
Major settlement
River
Fossil river
Panhandle
0
600 Kilometers
Permanent swamps
Seasonal swamps

Figure 0.2 The Okavango River Basin, showing drainage into the Okavango Delta and the
Makgadikgadi Pans

1.2
Delineation of the Okavango Basin into Integrated Units of
Analysis
Within the Okavango River Basin, no study could address every kilometre stretch of the river,
or every person living within the area, particularly a pilot study such as this one. Instead,
representative areas that are reasonably homogeneous in character may be delineated and
used to representative much wider areas, and then one or more representative sites chosen
in each as the focus for data-collection activities. The results from each representative site
can then be extrapolated over the respective wider areas.

Using this approach, the Basin was delineated into Integrated Units of Analysis
(EPSMO/Biokavango Report Number 2; Delineation Report) by:
dividing the river into relatively homogeneous longitudinal zones in terms of:
hydrology;
geomorphology;
water chemistry;
fish;
aquatic invertebrates;


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EFA Botswana Fish

vegetation;
harmonising the results from each discipline into one set of biophysical river zones;
dividing the basin into relatively homogeneous areas in terms of social systems;
harmonising the biophysical river zones and the social areas into one set of Integrated Units
of Analysis (IUAs).

The 19 recognised IUAs were then considered by each national team as candidates for the
location of the allocated number of study sites:
Angola: three
sites
Namibia: two
sites
Botswana: three
sites.

The sites chosen by the national teams are given in Table 0.1.

Table 0.1 Location of the eight EFA sites
EFA Site No
Country
River
Location
1 Angola
Cuebe
Capico
2 Angola
Cubango
Mucundi
3 Angola
Cutio Cuito
Cuanavale
4 Namibia
Okavango
Kapako
5 Namibia
Okavango
Popa
Falls
Panhandle at
6 Botswana
Okavango
Shakawe
7
Botswana
Khwai
Xakanaka in Delta
8 Botswana
Boteti Chanoga



IDENTIFICATION OF INDICATORS AND FLOW
CATEGORIES
1.1 Indicators
1.1.1 Introduction
Biophysical indicators are discipline-specific attributes of the river system that
respond to a change in river flow by changing in their:
abundance;
concentration; or
extent (area).

Social indicators are attributes of the social structures linked to the river that respond
to changes in the availability of riverine resources (as described by the biophysical
indicators).

The indicators are used to characterise the current situation and changes that could
occur with development-driven flow changes.


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EFA Botswana Fish


Within any one biophysical discipline, key attributes can be grouped if they are
expected to respond in the same way to the flow regime of the river. By example,
fish species that all move on to floodplains at about the same time and for the same
kinds of breeding or feeding reasons could be grouped as Fish Guild X.

1.1.2
Indicator list for Fish
In order to cover the major characteristics of the river system and its users many
indicators may be deemed necessary. For any one EF site, however, the number of
indicators is limited to ten (or fewer) in order to make the process manageable. The
full list of indicators was developed collaboratively by the country representatives for
the discipline ­ Dr. Ben van der Waal (Namibia), Miguel Morais (Angola) and
Ketlhatlogile. Mosepele (Botswana) - and is provided in Table 0.1. Further details of
each indicator, including the representative species of each biological one, are given
in Appendix A and discussed fully in Chapter 0.

Table 0.1 List of indicators for fish and those chosen to represent each site
Indicato
Sites represented ­ no more than ten
r
Indicator name
indicators per site
Number
1 2 3 4 5 6 7 8
1
Resident channel and lagoon dwellers, which
also undergo longitudinal migrations





x
x x
Small species that undertake lateral migrations




x
2
into seasonally flooded floodplains as major part

x
of their life history strategy
Large species that undertake lateral migrations




x
3
into seasonally flooded floodplains as major part

x
of their life history strategy
4
Rock dwellers








5
Marginal vegetation dwellers of the main channel




x
x x
and floodplain lagoons
Sandbank specialists




x
6
(Species that prefer clear, slow-flowing or quiet,

x
well vegetated water in the main channel)

7
Shallow, well vegetated backwater habitats
x x


1.1.3
Description and location of indicators
Indicator 1
Name:
Resident channel and lagoon dwellers, which also undergo
longitudinal migrations

Description:
These are normally characterized by clear, fast flowing deep
water of the main channel or large lagoons that are connected
to the main channel.

Representative species:
Tiger fish (Hydrocynus vittatus)


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Other characteristic species: Pink bream (Serranochromis robustus), Nembwe (S. giardi)
Flow-related location:
H. vittatus prefers well oxygenated water in the deep main river
channel and large lagoons. Both S. robustus and S. giardi
prefer deep main channel habitats and permanently flooded
lagoons. The latter prefers water bodies with sandy bottoms.

Known water needs:
H. vittatus undergoes longitudinal migrations to spawn on
flooded river banks where newly hatched larvae are transported
by receding water to the main channel. It is known to have
declined in some systems due to water abstraction, pollution
and dams (and weirs) which impeded their migrations. S. giardi
makes nests within dense vegetation in about 3 m water depth
while S. robustus nests along vegetated fringes of the main
channel in summer.
Indicator 2

Name:
Small species that undertake lateral migrations into seasonally
flooded floodplains as a major part of their life history


Description:
These seasonally flooded habitats are characterized by
relatively shallow, but clear water. The habitats normally have
sandy bottoms for the nest making species, and have different
kinds of submerged and emergent vegetation.

Representative species:
Silver catfish (Schilbe intermedius), bulldog (Marcusenius
macrolepidotus), and Petrocephalus catastoma

Other characteristic species: Synodontis spp.
Flow-related location:
M. Macrolepidotus prefers well-vegetated, muddy-bottomed,
marginal habitats of river channels while S. intermedius is a
pelagic species that prefers open water.

Known water needs:
M. macrolepidotus migrates into the shallow flooded floodplains
for breeding in shallow, vegetated water before they back-
migrate to the deeper waters. S. intermedius is normally found
in slow-flowing water with either emergent or submerged
vegetation. They also lay eggs on vegetation.

Indicator 3

Name:
Large species that undertake lateral migrations into seasonally
flooded floodplains as a major part of their life history


Description:
These seasonally flooded habitats are characterized by
relatively shallow, but clear water. The habitats normally have
sandy bottoms for the nest making species, and have different
kinds of submerged and emergent vegetation.

Representative species:
Red breast tilapia (Tilapia rendalli), three-spot tilapia
(Oreochromis andersonii) and green-head tilapia (O. macrochir)



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EFA Botswana Fish

Other characteristic species: Thin-face large-mouth (Serranochromis angusticeps), and
Catfishes, especially sharp-tooth catfish (Clarias gariepinus)
Flow-related location:
T. rendalli prefers well-vegetated water on river channel and
floodplain lagoons margins. O. andersonii prefers slow-flowing
or standing water in backwaters and floodplain lagoons. O.
macrochir prefers quiet waters along river margins, backwaters
and floodplain habitats. S. angusticeps prefers quiet backwater
habitats with dense vegetation.
Known water needs:
T. rendalli undergoes seasonal migrations to seasonally flooded
floodplains where it makes nests in shallow water. O.
andersonii undergo seasonal migrations into the seasonally
flooded floodplains where they breed and feed. Adults then
back-migrate to deep open water while juveniles remain among
littoral vegetation. O. macrochir undergo seasonal migrations
into seasonally flooded floodplains where they feed and make
nests in shallow water for breeding. S. angusticeps makes
nests in the flooded floodplains in 1-3 m deep water.

Indicator 4

Name:
Marginal vegetation dwellers of the main channel and floodplain
lagoons



Description:
These habitats are characterized by littoral vegetation on the
main channels and lagoons. They generally have deep, slow
moving water. The littoral vegetation is normally a mixture of
papyrus, reeds and hippo grass.

Representative species:
Sargochromis carlottae, Serranochromis macrocephalus,
Hepsetus odoe
Other characteristic species: Pollimyrus castelnaui, Synodontis nigromaculatus, C.
multispine,
Flow-related location:
S. carlottae prefers well vegetated habitats while S.
macrocephalus occurs more along the littoral vegetation of the
floodplain channels and lagoons. C. multispine, S.
nigromaculatus and P. castelnaui occur on marginal vegetation
of river channels and floodplain lagoons. Adult H. odoe prefer
quite, deep water while juveniles of H. odoe prefer well-
vegetated marginal habitats.


Known water needs:
S. carlottae prefers deeper water areas with sandy bottoms in
floodplain lagoons and river channels; S. macrocephalus feeds
near the bottom of channels and lagoons and breeds at low
water just before the onset of the floods H. odoe make bubble
nests in the dense vegetation of marginal habitats or the
shallow-well vegetated habitats of floodplains.

Indicator 5

Name:
Sandbank specialists; species that prefer clear, slow flowing or
quiet, well vegetated water along the main channel or side
channels off the main channel


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EFA Botswana Fish




Description:
These habitats are characterized by sandy banks, normally off
the main channels. The water here is normally very clear, is
slow moving or quiet, and is sometimes sparsely vegetated.

Representative species:
Brycinus lateralis, Barbus poechii, Leptoglanis rotundiceps
Other characteristic species:
Flow-related location:
B. lateralis shoal in clear, slow-flowing or quiet, well vegetated
water and these normally occur with B. poechii

Known water needs:
These species prefer sandy, shallow areas

Indicator 6

Name:
Shallow, well vegetated backwater habitats



Description:
These habitats are normally found either in the seasonal
floodplains or off the main channel in the backwaters. They are
characterized by shallow, standing/ quiet, clear and well
vegetated water.
Representative species:
Tilapia sparrmanii, Pharyngochromis acuticeps, Aplocheilecthys
johnstoni, A. hutereaui, Pseudocrenilabrus philander

Other characteristic species: Barbus paludinosus, Hemichromis elongatus, Barbus
multilineatus, Aplocheilichthys afrovernayi, Microctenopoma
intermedium

Flow-related location:
The Aplocheilichthys spp. prefer inshore, well vegetated water.
H. elongatus prefers clear, littoral area water, while T.
sparrmanii prefers quiet/ standing water with either submerged
or emergent vegetation. B. multilineatus and A. afrovernayi both
prefer quiet, well vegetated water while M. Intermedium occurs
in shallow, dense marginal vegetation
Known water needs:
Aplocheilichthys spp. prefer shallow water in the seasonal
floodplains. H. elongatus and T. sparrmanii make nests on the
substrate. B. multilineatus and A. afrovernayi prefer shallow
water. M. intermedium make bubble nests in water among the
aquatic vegetation of shallow water habitats.


1.2
Flow categories ­ river sites
One of the main assumptions underlying the EF process to be used in the TDA is that it is
possible to identify parts of the flow regime that are ecologically relevant in different ways
and to describe their nature using the historical hydrological record. Thus, one of the first
steps in the EFA process, for any river, is to consult with local river ecologists to identify
these ecologically most important flow categories. This process was followed at the
Preparation Workshop in September 2008 and four flow categories were agreed on for the
Okavango Basin river sites:
Dry season
Transitional Season 1


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EFA Botswana Fish

Flood Season
Transitional Season 2.

Tentative seasonal divisions for river Sites 1-5 are shown in Figure 0.1 to Figure 0.5. These
seasonal divisions will be formalised by the project hydrological team in the form of
hydrological rules in the hydrological model. In the interim they provide useful insights into
the flow regime of the river system suggesting a higher within-year flow variability of the
Cuebe River and a higher year-on-year variability of the Cubango River.

It is planned to use similar flow seasons for the remaining river sites: 6 and 8.

120
Wet
We
100
Trans 1
Trans 2
Dry
80
Year
Y
2
ear
60
Year
Y
1
ear
Year
Y
3
ear
40
20
0
O
N
D
J
D
F
M
A
M
J
J
M
J
A
S

Figure 0.1 Three representative years for Site 1: Cuebe River @ Capico, illustrating the
approximate division of the flow regime into four flow seasons


1200
Wet
1000
Trans 1
Trans 2
Dry
800
Year
Y
1
600
Year
Y
2
Year
Y
3
400
200
0
O
N
D
J
D
F
M
A
M
J
J
M
J
A
S

Figure 0.2 Three representative years for Site 2: Cubango River @ Mucindi, illustrating the
approximate division of the flow regime into four flow seasons




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EFA Botswana Fish

250
Wet
Dry
200
a
n
s 1
a
n
s 2
Tr
Tr
150
Year 1
ear
Year 2
ear
100
Year 3
ear
50
0
O
N
D
J
F
M
A
M
J
J
M
J
A
S

Figure 0.3 Three representative years for Site 3 Cuito River @ Cuito Cuanavale, illustrating
the approximate division of the flow regime into four flow seasons

1000
900
Wet
We
800
Dry
Dr
Tra
Tr n
a s
n 1
s
Tra
Tr n
a s
n 2
s
Dry
Dr
700
600
Year 1
500
Year 2
400
Year 3
300
200
100
0
O
N
D
J
F
M
A
M
J
J
M
J
A
S

Figure 0.4 Three representative years for Site 4: Okavango River @ Kapoka (hydrological data
from Rundu), illustrating the approximate division of the flow regime into four flow
seasons





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EFA Botswana Fish

1800
1600
Wet
1400
Dry
Trans
n 1
Trans 2
Dry
1200
1000
Year 3
000
Year 2
800
Year 1
600
400
200
0
O
N
D
J
F
M
A
M
J
J
M
J
A
S

Figure 0.5 Three representative years for Site 5: Okavango River @ Popa (hydrological data
from Mukwe), illustrating the approximate division of the flow regime into four flow
seasons

The literature review (Chapter 0) and data collection and analysis exercises (Chapter 0) are
focused on addressing what is initially expected to be nine main questions related to these
flow seasons (Table 0.2).

Table 0.2 Questions to be addressed at the Knowledge Capture Workshop, per indicator per
site. In all cases, `natural' embraces the full range of natural variability
Question
number
Season
Response of indicator if:
1
Onset is earlier or later than natural mode/average
2
Dry Season
Water levels are higher or lower than natural mode/average
3
Extends longer than natural mode/average
4
Duration is longer or shorter than natural mode/average - i.e. hydrograph is
Transition 1
steeper or shallower
5
Flows are more or less variable than natural mode/average and range
6
Onset is earlier or later than natural mode/average ­ synchronisation with
Flood season
rain may be changed
7
Natural proportion of different types of flood year changed
8
Onset is earlier or later than natural mode/average
Transition 2
9
Duration is longer or shorter than natural mode/average ­ i.e. hydrograph is
steeper or shallower


1.1
Inundation categories ­ delta sites
The recognised river flow categories are not relevant in the Delta, where inundation is the
major driver of ecosystem form and functioning. The main inundation categories recognised
by the inundation model developed by the Harry Oppenheimer Okavango Research Centre
(HOORC) are used here (Table 0.3).



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EFA Botswana Fish

Table 0.3 Inundation categories for the Okavango Delta as recognised by the HOORC
inundation model
Inundation
Inundation category name
Description
category
Delta 1
Channel in permanent swamp

Delta 2
Lagoons in permanent swamp

Delta 3
Backswamp in permanent swamp

Delta 4
Seasonal pools in seasonally flooded

zones
Delta 5
Seasonal sedgelands in seasonally flooded
zones
Delta 6
Seasonal grasslands in seasonally flooded
zones
Delta 7
Savannah ­ dried floodplain in seasonally

flooded zones
Boteti 1
Wet connected

Boteti 2
Disconnected pools

Boteti 3
Dry


LITERATURE REVIEW
Introduction
Both published and grey literature were used to find suitable information for this study.
However, while very little literature exists for the Okavango Delta, apart from the extensive
work done by Merron and Bruton (1988), most of the available published literature found was
for the Zambezi system. Most of this literature, especially old publications, were found in the
Peter Smith Collections at the HOORC library. Some internet searches also produced few
literature that were also used for this report. Notwithstanding, there is very little literature that
exists for the Okavango Delta that explores the relationship between flow and fish biology/
ecology.
The most comprehensive ecological study of the Delta's fish populations was done by
Merron and Bruton (1988) and Merron (1991). The general observations made from these
key studies indicated that the seasonal flow regime in the Delta is a major drive of change in
the Delta's fish communities. Skelton, et al (1985) observed that the annual flood pulse is a
major driving force in the Delta fish stocks. This was echoed by Mosepele (2008) who
highlighted that, similar to other flood pulsing systems worldwide, the delta's fish stocks are
also directly affected by the seasonal flood pulse. This observation concurs with Mosepele et
al (2009) who observed that the length of time the water is present in the floodplains and the
nature of its flow have a significant effect on the Delta's fish communities. Bell-Cross (1974)
observed that the timing, height and duration of annual floods are the main regulatory factors
of fish biomass in the neighbouring Zambezi system. Bell-Cross (1974) further observed a
positive correlation between fish production and prolonged flooding. According to Bell-Cross
(1974), as a consequence of poor rainfall, flood waters will recede from the floodplains and
tributaries earlier than usual with several potential effects on the Upper Zambezi fish stocks:
(i) increased fishing and natural mortality (i.e. predation pressure) where there will be limited
natural cover due to less water availability; (ii) juvenile fish will be forced out of their refuge
before they reach adequate size which will make them more vulnerable to predation from a
greater size range of predatory species and for a longer period. Moreover, the backwater
habitats and lagoons which are normally utilized by sub-adult fish will dry out and be
uninhabitable as refuge for juvenile fish; (iii) potentially increased natural mortality (due


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EFA Botswana Fish

mainly to predation) of juveniles of some commercial species which spawn in the main
channel just before the onset of flooding.

Chapman and Chapman (1993) observed seasonal variations in fish abundance in the River
Sokoto (Nigeria). They concluded that spawning success, migration, habitat partitioning,
mortality and other "random trapping of individuals as waters fall" may account for their
observations in fluctuating abundance of fish in the Sokoto system. Furthermore, Chapman
and Chapman (1993) discussed that spawning success and mortality are affected by the
onset and duration of flooding in the Sokoto system. Smaller fish may escape predation
pressure in floodplain pools through an earlier rise in water levels where there may be a high
concentration of predators by the end of the dry season. Moreover, they also observed that
longer duration floods may be beneficial to multiple spawners such as Tilapia spp. and
Oreochromis spp. Notwithstanding, Chapman and Chapman (1993) also highlighted that
unpredictability in the magnitude and duration of flooding may result in some fish getting
trapped in floodplain pools. They observed that a faster rate of flood level decline in the
1956-1957 flooding season resulted in a high proportion of migratory species/ fish getting
trapped in floodplain pools in the Sokoto system. However, it is equally important to note that
density dependent factors on fish populations will also begin to play a major role on fish
stocks in floodplain pools/ lagoons as the dry season progress. According to Chapman and
Chapman (1993) they may result in heavy pressure on available food and limited space
which will increase both intra and inter specific competition for resources.

Merron and Bruton (1988) concluded that the breeding cycle of most Delta species is directly
influenced by the flood regime. Furthermore, they also observed that the seasonal flood
pulse opens up new littoral habitat seasonally which acts as nurseries for most fish species.
While the Delta might be an unstable system due to the seasonal flood regime, its fish
species are highly resilient because they persist in space and time (Merron and Bruton,
1988). According to Bell-Cross (1974), an increase in water velocity is the first trigger of fish
migrations in the Upper Zambezi system. After movement has been initiated, then the depth
dependency factor becomes important, where lack of "acceptable water depth" regulates any
further movements of certain size classes of fish within each species group. Based on this
observation, Bell-Cross (1974) highlighted that the first fish species to migrate laterally are
small sized species that have a low a depth-dependency factor, and juveniles of some large
species which breed before the floods arrive, such as some cichlid species. Bell-Cross
(1974) observed that the depth dependency factor might be the major factor regulating fish
back-migrations to the main channel. Kapoor and Khanna (2004) observed that freshwater
fish undertake migrations either for foraging or breeding purposes. They concluded that
water current is used as a major cue for orientation during migrations, where the direction of
water flow orients a fish. Therefore, apart from Bell-Cross's (1974) depth dependency factor,
Kapoor and Khanna's (2004) observations suggested that back-water flow from the drying up
floodplains may be the environmental cue for fish species to start back-migrating into more
permanent/ deeper water. Notwithstanding, Chapman (1995) observed that depth was a
major factor regulating the dispersal of Clarias liocephalus in the Rwembaita Swamp
(Uganda). However, Chapman et al (1998) also found a positive relationship between high
saturated oxygen levels in floodplain water and peak flood periods. Subsequently, they
(Chapman et al., 1998) discussed that dissolved oxygen is limiting during the dry season
period. Therefore, low flood periods, while contributing towards density dependent factors
regulating fish abundance and production, might also cause low dissolved oxygen which
would also be detrimental to fish stocks. Subsequently, Chapman and Liem (1995) had
observed that the relative Barbus neumayeri during the dry season in the Rwembaita Swamp
was positively correlated to dissolved oxygen levels and not depth.

These pulses in fish migrations, caused by the seasonal flood pulse, cause variations in fish
catch rates. This observation agrees with Welcomme (1985) that fish catch rates in floodplain
systems are affected by dilution and concentration factors, and this has been established for


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EFA Botswana Fish

the Delta (Merron and Bruton, 1988; Mosepele, 2000). Cued by the seasonal flood pulse,
species either undergo longitudinal or lateral migrations in the Delta primarily for feeding and
breeding purposes (Merron and Bruton, 1988; Merron, 1991). This observation agrees with
Chapman (2001) who concluded that fish in the Congo River undergo migrations for feeding
and breeding purposes. Chapman and Liem (1995) made similar observations that the
seasonal dispersal of Barbus neumayeri in the Rwembaita Swamp is not restricted to
spawning individuals only. Moreover, fish growth during the high flood period tends to be
faster due to high food availability (Chapman, 2001) compared to low flood periods when
density dependent factors are major regulating factors. Moreover, while some species might
spawn throughout the year (i.e. multiple spawners), their peak spawning normally coincide
with high flooding.

As a counterpoint to lateral and longitudinal migrations caused by the arrival of the flood,
Bell-Cross (1974) described dry-season fish migrations of small-sized fish species along the
margins of the main channel in water of 1-m or less depth. These small-sized species form
shoals which might include (but are not restricted to) Barbus barotseensis, B fasciolatus, B.
paludinosus, Hemigramocharax multifasciatus, Aplocheilichthys johnstoni, juvenile Labeo
lunatus and Tilapia sparrmanii. Possibly, the stimulus for these upstream migrations is water
velocity, because Bell-Cross (1974) observed that these upstream migrations might last for
only several weeks when the water velocity is still relatively high in the Zambezi (April -
June). Subsequently, these migrations cease completely which is attributed to either a
substantial decrease in water velocity or intense predation by species such as H. vittatus.
Conversely, Bell-Cross (1974) suggested that larger sized species are more territorial during
the dry season period.

Lindholm et al (2007) observed that "seasons of large and long lasting floods cause
improved circulation and enhanced reproductive success for fish". This is based on the
observation that low floods constrained fish migrations into the floodplains which severely
affected recruitment. Subsequently, Lindholm et al (2007) observed that fish abundance
during a high flood was almost double (i.e. 2x) that at low flood levels. This intimate
relationship between general fish ecology/ biology (or fish production) and the flood regime is
also highlighted by Mosepele et al (2009). They (Mosepele et al 2009) observed that the
seasonal flood pulse does not only open new habitat to fish colonization, but that seasonal
flooding also drives fish breeding and subsequent recruitment into the Delta fishery which is
ultimately utilized by both subsistence, commercial (albeit small scale) and recreational
fishers. Furthermore, Mosepele et al (2009) observed that maintaining the Delta's ecosystem
as the mainstay of abundant fish and wildlife resources requires and deep understanding of
the Delta's flow requirements and "then using this understanding to allocate water in the rest
of the Okavango watershed". Subsequently, Mosepele et al (2009) modified the existing
WEAP model to incorporate environmental needs (in this case fish and flows). One basic
assessment made under this model was that minor hydrologic manipulations upstream would
have minimal impact on the Delta's ecosystem. However, Mosepele et al (2009) concluded
that a more holistic and comprehensive approach, that incorporates conflicting water uses, is
needed "to fully understand the interactions between upper basin management and
ecosystem status in the delta". Therefore, it is envisaged that this current approach will
address most of the concerns raised by Mosepele et al (2009) using their conceptual
approach.




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EFA Botswana Fish

1.1
Indicator 1: Main channel/ open water species
1.1.1 Main characteristics of Indicator 1
The fish species in this indicator spend most of their adult life history in the deep, open
waters of the main channel and deep, large lagoons and oxbow lakes which are connected
to the main channel. According to Merron (1991), water permanency, depth and flow are
some of the major ecological factors limiting the distribution of Hydrocynus vittatus in the
Okavango Delta. Therefore, H. vittatus occurs in the more hydrologically stable and
permanent parts of the Delta (Merron and Bruton, 1988; Merron, 1991). Winemiller and
Winemiller (1994) also made a similar observation that adult H. vittatus prefer more riverine
habitats and large lagoons and are not found in seasonally flooded floodplains. In the
Zambezi system (main channel of Zambezi and Chobe rivers), H. vittatus was found to occur
at mid-water depth within the water column, in fast flowing water. According to Winemiller
(1991), S. robustus and S. giardi in the Upper Zambezi prefer deep portions of the main
channel habitats close to the bottom and near high sand banks. S. robustus prefer moderate
to swift flowing water, while S. giardi prefer slow, swirling water currents (Winemiller, 1991).
For the upper Zambezi, Winemiller (1991) described S. robustus as a "river-dwelling,
epibenthic, diurnal piscivore" while S. giardi as described as a "river-dwelling molluscivore".

Hydrocynus vittatus, which is a key species in this guild is a key recreational species that
sustains the Delta's recreational fishery. However, S. robustus is also a key recreatioanlly
harvested species in the Delta's fishery (Mosepele et al 2003). Based on data available,
Mosepele and Nengu (2003) estimated that the maximum size (i.e. L ) that H. vittatus can
reach is 68 cm total length (though fork length is normally the preferred length for this
species), while they estimated a maximum total length of 56 cm for S. robustus.
Nothwithstanding, estimates from the Fishbase database (www.fishbase.org) based on data
from Rwanda estimated a total length of 105 cm for H. vittatus. The database indicates that
this species has a life span of 11 years, and reaches sexual maturity between 27 and 40 cm .


1.1.2 Life cycle attributes of Indicator 1
Skelton (2001) observed that H. vittatus undergo longitudinal migrations in the main channels
in search of suitable spawning/ breeding habitat. According to Merron (1991), H. vittatus
breeds in early summer on the shallow littoral areas (along papyrus vegetation) of the main
channels and oxbows lagoons. They undergo longitudinal migrations in the main channel on
feeding forays and also in search of optimum breeding habitat. Due to the cannibalistic
nature of this species (Merron and Bruton, 1988; Merron, 1991; Winemiller and Winemiller,
1994), there is a strict habitat partitioning of the different size classes of H. vittatus, where
juvenile/ sub-adult fish are found in slower flowing and more vegetated water while adult fish
are found in more open, fast flowing water (Merron and Bruton, 1988). This agrees with
Winemiller and Winemiller (1994) who observed habitat partitioning between young-of-the-
year and adult H. vittatus in the Zambezi system.


1.1.3
Links to flow
H. vittatus
While Winemiller and Winemiller (1994) observed that breeding of H. vittatus may be
positively correlated to the duration of the annual flood, Merron and Bruton (1988) observed
that H. vittatus spawns in early summer in the Delta (before the onset of the annual floods).


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EFA Botswana Fish

This agrees with Kenmuir's (1973) observation from Lake Kariba that the duration of
breeding of H. vittatus is tied to the duration of river flow. It is on this basis that Kenmuir
(1973) observes that the presence of atrophied female H. vittatus gonads in the Mwenda
area could be attributed to female fish waiting for too long for "the river to start flooding
sufficiently." flood properly. Kenmuir (1973) also observed that the atrophied gonads could
also have been caused by the river stopping flowing before female fish had reached a "fully
ripe laying condition."

Merron and Bruton (1988) observed that H. vittatus spawns in the papyrus fringe of the main
channel and ox-bow lakes. According to Merron (1991), H. vittatus is predominantly found in
the main channel habitat, characterized by high water retention, with a mean depth of 2.5 m
and relatively fast flowing water (i.e. a water flow rate of approximately 2-7 m/ sec). H.
vittatus prefers a sandy substrate, with abundant emergent vegetation, some fairly common
submerged vegetation, and some floating vegetation. Furthermore, Winemiller and
Winemiller (1994) observed that water depth is possibly one of the major limiting factors for
the distribution of H. vittatus. According to some past research (Merron and Bruton, 1988;
Merron, 1991), juvenile H. vittatus (age 1) stay in the shallow, well vegetated areas in the
littoral areas of the main channel and large lagoons (and ox-bow lakes/lagoons) connected to
the main channel. Sub-adult H. vittatus (age 2) inhabit tributary channels off the main
channel while adult fish (age 3+) inhabit the deeper and open water habitats of the main
channel and large lagoons (and ox-bow lakes/ lagoons).

H. vittatus has an ontogenetic feeding behaviour, where juvenile fish are primarily
insectivorous while adults are mainly piscivorous (Merron and Bruton, 1988; Skelton, 2001).
Notwithstanding, Kenmuir (1973) observed that H. vittatus fry in Lake Kariba graze
zooplankton heavily, perhaps on account of their preferred habitat at this age (shallow, well
vegetated habitats with slow flowing water) Winemiller and Winemiller (1994) observed a
seasonal shift in the diet of H. vittatus in the upper Zambezi. At high flood levels, its top three
prey items were Hepsetus odoe, cichlids (unidentified) and haplochromine cichlids
respectively. Conversely, the top three prey items for H. vittatus at low flood levels were
Synodontis sp., haplochromine cichlids and momyrids respectively. According to Merron and
Bruton (1988) adult H. vittatus congregate at outlets of floodplain channels at receding floods
and prey heavily on Barbus sp which are back-migrating into the main channel due to drying
out floodplains. This observation agrees with Kenmuir's (1973) observation that H. vittatus
feeding activity increased with decreasing lake levels in Kariba.


Serranochromis robustus and Sargochromis giardi

Winemiller (1991) observed that S. robustus and S. giardi in the Upper Zambezi appear to
spawn just prior to flooding. This observation on S. giardi agrees with Bell-Cross (1975) who
observed that S giardi's breeding season coincides with the rainy season, which occurs
between October and February in the Upper Zambezi.

While their sample size was extremely small (15 fish) and the time series too short to make
any conclusive statements(6 months), Okland et al (2002) observed that S. robustus prefers
water depths of around 3.7 m in the Zambezi River. Okland et al (2002) also observed that S.
robustus prefers water with sandy substrates. Notwithstanding, Winemiller (1991) observed
seasonal shifts in the population structure of S. robustus in the Upper Zambezi. There was a
higher abundance of smaller/ younger fish during falling water levels while the population
was dominated by larger/ older fish at low floods. The higher proportion of younger/ smaller
S. robustus at falling floods was attributed to spawning that occurred just prior to or during
the peak flooding. Subsequently, the higher proportion of older/larger S. robustus at low
floods was attributed to increased predation on juvenile fish and "growth in the absence of


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EFA Botswana Fish

spawning activity that would add new recruits to the smallest size classes" (Winemiller,
1991).

S. giardi in the Upper Zambezi has an ontogenetic feeding pattern where younger fish fed
mostly on aquatic invertebrates, while older fish fed primarily on bivalve molluscs and
Trichoptera larvae off the sandy substrate. S. robustus also showed an ontogenetic feeding
pattern where younger fish preyed more on Barbus sp and less on juvenile Synodontis sp
while older fish preyed on juvenile Synodontis sp and less on Barbus sp (Winemiller, 1991).

1.1
Indicator 2: Small species that undertake lateral migrations into
the shallow, seasonally flooded floodplains
1.1.1 Main characteristics of Indicator 2
These are small sized species which migrate into the flooded floodplains seasonally with the
arrival of the annual flood. Generally, floodplain species, especially small sized individuals
such as in this guild, are characretrised by fast and seasonal growth patterns as a
consequence of seasonality in flooding (MRAG, 1994), which sugests that they have a high
degree of relience to environmental variability. According to Mosepele and Nengu (2003), M.
Macrolepidotus, which is a key species in this guild, can reach a maximum size (i.e. L ) of
approximately 20 cm total length. Based on Fishbase (www.fishbase.org), M. macrolepidotus
lays 6000 eggs, reaches sexual maturity between 11 and 15 cm, and spawns during teh
rainy season. According to the Fishbase database (www.fishbase.org), S. intermedius lays
approximately 18 000 eggs, is a non-guarder, spawns throughout the year, lives to about 5
years and reaches sexual maturity between 11 and 16 cm total length. Furthermore, while
larger sized M. macrolepidotus might prefer large floodplain lagoon habitats, smaller sized M.
macrolepidotus undertake seasonal migrations to the main channel at receding flood levels
where they are subsequently preyed upon by C. gariepinus. According to Kramer (1999), C.
gariepinus preys more heavily on male M. macrolepidotus than females primarily because
the male's produce an electric discharge. This high preference for M. macrolepidotus is
perhaps based on Hanika and Kramer's (2000) observation that C. gariepinus is electro-
receptive and may home in onto electric discharges of M. macrolepidotus. S. intermedius is
one of the most abundant and ubiquitous species in the Okavango Delta (Merron and Bruton,
1988; Mosepele et al, 2005) and is normally a shoaling species found in slow flowing water
(Merron and Bruton, 1988).
According to Mosepele et al (2003), these species are harvested by subsistence fishers
using a variety of fishing gears (e.g. fishing baskets, fishing weir, traditional hook and line,
etc). Notwithstanding, the small sized species in this guild are all important subssitence
fishery species and are key sources of food security during times of food scarcity (Mosepele
et al 2006). Furthermore, subsistence fishing (for these species) is an important social safety
net in the Delta that acts as a buffer for households against HIV/AIDS related stressors and
chronic poverty (Ngwenya and Mosepele, 2007). Notwithstanding all these, availability of
these species to exploitation (and that of floodplain species in general (Welcomme, 1985)) is
subject to concentration and dilution effects because of the hydrological regime (Mosepele,
2000; Mmopelwa et al 2009). However, subssistence fishers have developed differeht coping
mechanisms to exploit these species optimally despite the observed spatio-temporal
varaitions in availability (Mmopelwa, et al 2009). Moreover, the spatio-temporally diffused
nature of the fishery (Mosepele and Mosepele, 2005) controlled by a flood pulse (Mosepele,
2008) pose daunting fisheries management challenges.



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EFA Botswana Fish

1.1.2 Life cycle attributes of Indicator 2
S. intermedius

According to Mosepele et al (2005), S. intermedius is an opportunistic predator with an
ontogentic feeding behaviour which makes it a successful predator in the Delta. Because of
its feeding ecology, this species feeds on a wide variety of species ranging from aquatic and
terrestrial invertebrates by younger/ juvenile fish to being piscivorous as the fish grow older
(Merron and Bruton, 1988; Merron, 1991; Mosepele et al, 2005). Furthermore, S. intermedius
is known to prey heavily on termites that normally appear just after the summer rains (Merron
and Bruton, 1988; Mosepele et al, 2005). Merron and Bruton (1988) observed that S.
intermedius' breeding cycle is closely tied to the arrival of annual flood waters in the
Okavango Delta
1.1.3
Links to flow

M. macrolepidotus

Merron (1993) observed that large populations of smaller-sized M macrolepidotus (i.e. <140
mm) start back-migrating from the floodplains into the main channel of the Delta at receding
flood levels (i.e. starting from around August in the Upper Delta). According to Merron
(1993), this is possibly a dispersal mechanism which is caused by limited space in floodplain
lagoons, where the larger M macrolepidotus remain and breed throughout the summer
months as observed by Merron and Bruton (1988).

1.2 Indicator 3: Large species that undertake lateral migrations into the
shallow, seasonally flooded floodplains
1.3
Main characteristics of Indicator 3
These are large sized species that undergo seasonal lateral migrations as a consequence of
the seasonal flood regime. According to Mosepele and Nengu (2003), specis such as O.
andersonni can reach a maximum size (i.e. L ) of 53 cm total length, T. rendalli can reach a
maximum size of 47 cm while O. macrochir can reach a maximum size of 40 cm, making it
the smallest of these cichlids. Nonetheless, it has been observed that similar individuals of
same species from upper and lower Delta habitats have different growth rates. Generally
upper Delta individuals appear to growth slowly and reach bigger sizes while lower Delta
individuals grow faster and reach smaller sizes (Tweddle et al 2003; Mosepele et al, 2005).
Adult O. andersoni spend most of their time in the main channel (s) of the Delta while O.
macrochir is found mostly in slow flowing channels and lagoons and some well-vegetated
backwater lagoons (Merron and Bruton, 1988). Furthermore, while C. gariepinus is generally
ubiquitous in the Delta, its major inclusion in this indicator is based on its strong seasonal
behaviour where it congregates in hunting packs and preys heavily on smaller sized species
that back-migrate to the main channel at receding flood levels from the floodplains.
Notwithstanding, these three cichlid species (i.e. O andersoni, O. Macrochir and T. rendalli)
are key commercially harvested species in the Delta (Mosepele, 2000; Mosepele and
Kolding, 2003; Mosepele et al, 2003) and have sustained a commercially viable and vibrant
small scale commercial fishery in the Delta (Mmopelwa et al, 2005). Commercial fishers
employ indigenous traditional knowledge to selectively harvest these species in the Delta
(Mosepele et al 2007). Despite consistent concerns about commercial over-exploitation of
these key species that has resulted in various forms of conflict (Kolding, 1996; Mosepele
2000; Tweddle et al 2003), assessments of the fishery using various indicators such as a


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EFA Botswana Fish

classical length based assessment (Mosepele and Kolding, 2003), trends in catch per unit of
effort (i.e. cpue expressed as kg/fisher/ year) by Kgathi et al (2005), trends in mean length
over time and reaction time of this fishery (i.e. cichlids) to the flood regime (Ntsima, 2008),
there has been no indications of biological over-fishing observed. The greatest management
challenge facing this fishery, and floodplain fisheries in general, is to not only implement
policies based on classical fisheries management approaches that have failed elsewhere
(Mosepele, 2008), but to also find the balance between traditional user rights and modern
management approaches (Mosepele et al 2007) based on a co-management approach (Jul-
Larsen et al 2003).

1.3.1 Life cycle attributes of Indicator 3
Oreochromis andersoni and O. macrochir

While O. macrochir in the Upper Zambezi commence breeding in the early summer months
before the onset of the floods, they also breed during the high flood period in the floodplains
(after undergoing lateral migration). Juvenile O. macrochir then remain in floodplain lagoons
and backwaters until they are large enough to co-exist with H. vittatus in the main channel
habitat (Bell-Cross, 1974).

C. gariepinus

In the Zambezi, C. gariepinus commence breeding during the middle of the rainy season
when adults undergo lateral migrations to spawn on the shallow, newly inundated grassy
floodplains (Bell-Cross, 1974). C gariepinus spawns in shallow floodplains and slow flowing
river channels where the eggs hatch after 24 hours and the fish fry/ larvae are free-swimming
start feeding/ foraging around 80 hours (2-3 days) after being hatched (Merron and Bruton,
1988; Skelton, 2001). According to Skelton (2001), the larvae remain under vegetation cover
in littoral areas, presumably to hide from predators. While growth is rapid, it is affected by
local conditions but they may grow to about 200 mm (SL) within the first year (Skelton, 2001).

1.3.2
Links to flow
Oreochromis andersoni, O. macrochir and Tilapia rendalli

According to Bell-Cross (1974), periphyton is the most important diet of juvenile fish of
commercially important species like Oreochromis andersoni and O. macrochir, which are
normally found in the quiet, slow flowing waters of seasonally flooded floodplains. While T
rendalli is primarily a herbivore, it also feeds on detritus, aquatic and terrestrial insects. It
makes nests in shallow water of not more than 2-m depth in floodplains (Bell-Cross, 1974).
On the other hand, Merron and Bruton (1988) observed that O. andersoni make nests on a
sandy substrate in water of between 0.2 ­ 2 m depth. Merron and Bruton (1988) highlighted
that one month after the eggs are hatched, the fish fry move into very shallow littoral habitats
in floodplains where they maximise growth due to the relatively high temperatures.

Bell-Cross (1974) observed that there was intense predation on young cichlids (juveniles and
sub-adults) during years of poor rainfall in the Zambezi because the fish are then restricted to
the permanent channels only. Merron and Bruton (1988) observed an extended and large
scale breeding/spawning for O. andersoni in the Delta which they associated with the high
floods of 1984 that had maintained high water levels and created extensive flooded areas.
Conversely, they (Merron and Bruton, 1988) also observed a significant decrease/ decline in


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EFA Botswana Fish

the proportion of spawning/ breeding female fish in 1985, which was a year of poor floods
and high water temperatures.

According to Merron and Bruton (1988), T. rendalli spawn between September and March,
where upper Delta populations have an extended spawning/ breeding season compared to
the lower Delta populations. They also observed that T. rendalli spawn on cleared substrate
and the parents guard the eggs until they hatch. The hatched larvae are then transferred to
nest holes where they are guarded by the parents until they start to swim freely and become
independent off their parents (Lowe-McConnell, 1975).

C. gariepinus

According to Merron and Bruton (1988), spawning for C. gariepinus varies based on location.
In the upper panhandle, C. gariepinus spawns during February and March at the peak of the
flooding season (measured at Mohembo) where they migrate to seasonally flooded grassy
floodplains, where their eggs are attached to aquatic vegetation. Notwithstanding, Merron
(1993) observed an increase in the reproductive condition of C. gariepinus with pack-hunting
in the upper Delta. While only 20% of the sampled pack-hunting C. gariepinus were ripe
running at the start of their annual feeding migrations in October, a higher proportion (70%)
of ripe running females was observed at the end of the pack-hunting feeding migrations in
mid-December. In the lower Delta, C. gariepinus spawns between September and
December.
Depending on the timing, duration and magnitude of the annual flood season, C. gariepinus
form pack-hunting shoals between August and mid-December annually (Merron and Bruton,
1988; Merron, 1991, 1993). During this time, they prey heavily on momyrids (specifically on
M. macrolepidotus and P. catastoma) (Merron and Bruton, 1988; Merron, 1991, 1993;
Hanika and Kramer, 2000) and to a lesser extent on other fish species such as Schilbe
intermedius, T. sparrmanii and Barbus sp (Merron and Bruton, 1988; Merron, 1991, 1993).
According to Merron (1993), average water depth where C. gariepinus feed during this time
(between August - December) is approximately 0.5 m and the shoals normally extend about
20 m into the papyrus fringe. A similar pack-hunting behaviour was observed by Bell-Cross
(1974) in the Zambezi where C. gariepinus prey heavily on smaller fish back-migrating from
the drying up floodplains. Merron (1993) further highlighted that pack-hunting C. gariepinus is
a predictable response of predators to changes in the Delta's flood levels.



1.4 Indicator
4:
marginal vegetation dwellers of the main channel
and floodplain lagoons
1.4.1 Main characteristics of Indicator 4
Winemiller (1991) observed that large S. altus prefer mid-depth water habitats or near
surface areas beneath or adjacent to dense stands of aquatic marginal vegetation usually at
the interface between swift downstream current and slower back eddies of the main channel
of the upper Zambezi. This observation agrees with Skelton (2001) who highlighted that S.
altus is found inshore from well vegetated river banks. H. odoe builds nets in the shallow,
seasonally flooded floodplain habitats as part of its life history.. Furthermore, H. odoe is a top
predator in the lower Delta (in the absence of H. vittatus) as observed by Merron and Bruton
(1988) and it subsequently has a regulatory impact on the fish community of the lower Delta.
H. odoe is also an important subsistence fishery species (Mosepele al, 2003).


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EFA Botswana Fish

1.4.2 Life cycle attributes of Indicator 4
H. Odoe

H. odoe spawns between September and March in both the upper and lower portions of the
Okavango Delta (Merron and Bruton, 1988) where it lays bubble/ foam nests among aquatic
vegetation of seasonally flooded floodplains or even on the aquatic vegetation on the
margins of main channel habitats in the lower Delta (Merron and Bruton, 1988).

1.4.3
Links to flow
H. odoe

Winemiller and Winemiller (1994) observed seasonal changes in the diet of H. odoe in the
Upper Zambezi. At low flood levels, Haplochromine cichlids constituted the highest
proportion (30.3%) of the diet of H. odoe, followed by momyrids and other H. odoe
respectively. Conversely, while Haplochromine cichlids still constituted the highest proportion
of the H. odoe diet at high floods, this proportion was much higher than at low floods (i.e.
49% vs. 30.3%), followed by momyrids and some Tilapia sp. This observation suggests that
H. odoe is more cannibalistic at low floods, possibly due to increased intra-specific
competition caused by reduced space.


1.5 Indicator
5:
sandbank specialists: Species that prefer clear,
slow flowing or quiet well vegetated water in the main channel

1.5.1 Main characteristics of Indicator 5
This indicator refers primarily to species that either prefer sandy banks of the main channel,
or species that prefer slow flowing, clear water of the main channel and large lagoons. Some
species in this indicator (Leptoglanis ) spend most of their time covered in the clean, white
sand substrate, while other species (Brycinus lateralis and Barbus poechii) spend most of
their time feeding either from the water surface for terrestrial insects or feeding among the
aquatic vegetation for aquatic macro-invertebrates.

1.5.2 Life cycle attributes of Indicator 5
While very little is known about the biology of Leptoglanis rotundiceps, this species is known
to bury itself in sand and snap/ grab at passing food particles/ prey. This species is also
known to be an early summer spawner (Merron and Bruton, 1988).
1.5.3
Links to flow
B. lateralis has an omnivorous diet comprising of both plant material and aquatic macro-
invertebrates (e.g. gastropods, bivalves, crustaceans, etc). Merron and Bruton (1988)
observed that plant material; especially seeds and fruits from marginal and submerged plants
like Nymphea sp constitute a significant proportion of the diet of this species. In this case, B.
lateralis is an important conduit of energy from the terrestrial to the aquatic habitats.




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EFA Botswana Fish

1.6
Indicator 6: Shallow, well vegetated backwater habitats
1.6.1 Main characteristics of Indicator 6
This indicator refers to species which spend most of their time in the shallow, well vegetated
backwater habitats off the main channel or seasonal floodplain habitats. These species are
normally found in slow flowing water among aquatic vegetation, while some species such as
the A johnstoni can also be found in the fast flowing waters of the channel habitats at low
flood periods.
Most of the small sized cichlids that are found in this guild (i.e. T. Sparrmanii, H. elongatus,
P. philander, etc) are harvested by the subsistence fishery using fishing baskets by women
predominantly (Mosepele et al 2003) and constitute a major buffer during lean periods
(Mosepele et al, 2006).

1.6.2 Life cycle attributes of Indicator 6
Chapman and Liem (1995) observed that the reproductive activity of a cyprinid, Barbus
neumayeri, increased during seasonal flooding, which agrees with Merron and Bruton's
(1988) observation that the reproductive activity of most cyprinids in the Delta is regulated by
the seasonal flood regime
1.6.3
Links to flow
C. multispine
This species is not common in the fast flowing waters of the upper Delta and is found more in
the slower flowing shallow floodplain habitats in the lower Delta (Merron and Bruton, 1988).
According to Merron and Bruton (1988), C. multispine is sometimes found in rain pools
shortly after heavy rains because of its ability to crawl over wet ground to other habitats.
Furthermore, Skelton (2001) observed that C. multispine also preys on small fish and aquatic
macro-invertebrates.


1.7 Summary
As already indicated, floodplain fish have fast growth rates and variable growth patterns on
account of the seasonal flood regime. Moreover, because of the nature of the environment
they live in, they have relatively elastic life history strategies which allows them to adapt to
different macro and micro ecosystems that are found within the Delta. Therefore, while six
guild/ indicators were developed for the Delta based on their habitat preferences, these
indicators still need to be refined further with more basic research to establish some of the
observations and associations that were made in this chapter. Species such as C. gariepinus
and S. intermedius are fairly ubiquitous in the Delta and is found in any particular habitat. O.
andersoni is a pioneer species that has found been found in either drying out isolated pools
in the seasonal floodplains or was observed colonizing a recently inundated sump lake in the
Delta (i.e. Lake Ngami). Even more interesting was that while O. andersoni is recorded in
published literature as a detritivore, it was feeding voraciously on cyprinids in Lake Ngami.
Therefore, there is need for more basic research to establish quantitative relationships
between flow variability, habitat partitioning and fish population dynamics in the Delta.


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EFA Botswana Fish

DATA COLLECTION AND ANALYSIS
No new data were collected for this study.



1.8
Methods for data collection and analysis
Data collected on long term monitoring projects was used in this study and none was
collected specifically for this project.

1.9 Results
No new data

1.10 A summary of present understanding of the predicted
responses of all fish indicators to potential changes in the flow
regime
The following tables summarize predicted response of the fish indicators developed in this
study due to changes in the flow regime of the Delta and the Boteti River.




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EFA Botswana Fish

5
DATA COLLECTION AND ANALYSIS

Methods for data collection and analysis
This report is based on fieldwork on birds conducted during the period 2000 to the present,
and not on any specific work for this project. Previous fieldwork is summarized below:
Extensive aerial surveys of the whole Delta censusing Wattled Cranes, during 2001, 2002
and 2003. This was supported by groundwork monitoring breeding success of nesting pairs
Fieldwork gathering data for a baseline study of the Slaty Egret during 2004 and 2005.
AquaRap 2003 ­ birds were surveyed at two of the sites relevant to this project (viz.
Shakawe and Xakanaxa) as well as at other sites, which provided the basis for selecting the
indicator species at these sites.
African Waterbird Census data ­ these waterbird counts are conducted biannually (mid-
winter and mid-summer) throughout the Okavango Delta and provide detailed information on
the numbers and distribution of waterbirds which can be related to water flow levels. The
three sites for this project have been regularly surveyed in the past ­ for some sites the
dataset spans almost two complete decades.

A summary of present understanding of the predicted responses of all bird
indicators to potential changes in the flow regime
The following tables summarise general responses of the indicator species to dry season
variables, flood season variables and the transition between flood and dry seasons. It must
be emphasised that these are general reponses as they are not area specific.



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EFA Botswana Fish

4.11.1 Fish Indicator 1 ­ Resident in river
Table 0.1 Predicted response to possible changes in the flow regime of fish resident in river in the Okavango River ecosystem
Confidence in
Question
Season
Possible flow change
Predicted response of indicator
prediction (very low,
number
low, medium, high)
Onset is earlier or later than
Relatively negligible if later because it might result in a prolonged spawning season which is good
1
High
natural
Negative if earlier because then it shortens breeding season which might affect recruitment
Dry Season
Water levels are higher or lower
Higher water levels might have a positive effect
2
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
High
3
Extends longer than natural
Negative because it might affect spawning/ breeding and feeding
High
Duration is longer or shorter than
A steep rise in water levels will have negative effects
4
natural - i.e. hydrograph is
A longer rise will have relatively positive effects
medium
Transition 1
steeper or shallower
5
Flows are more or less variable
The effects might be negligible - Nil
low
than natural
Onset is earlier or later than
The effects may be negligible if synchronisation with rain is changed.
6
natural ­ synchronisation with
Earlier onset might be positive while later may be negative
medium
Flood season
rain may be changed
Natural proportion of different
Higher floods than normal are always good for general floodplain fish production
7
medium
types of flood year changed
Lower floods than normal are always negative for general floodplain fish production
Earlier decrease may affect fish recruitment negatively
8
Onset is earlier or later than
Late decrease may affect fish recruitment positively
high
natural

Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on larval fish back-migrations into main channel
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
medium
steeper or shallower




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EFA Botswana Fish

4.11.2 Fish Indicator 2 ­ Small fish migrating to floodplains
Table 0.2 Predicted response to possible changes in the flow regime of small fish migrating to floodplains in the Okavango River ecosystem
Confidence in
Question
Season
Possible flow change
Predicted response of indicator
prediction (very low,
number
low, medium, high)
Might be beneficial if later because it might result in a prolonged spawning season hence facilitating
Onset is earlier or later than
1
natural
increased fish production
High
Negative if earlier because then it shortens breeding season which might affect fish production
Dry Season
Water levels are higher or lower
Higher water levels might have a positive effect on fish production
2
medium
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
Negative because it might affect spawning/ breeding and feeding. However, catfishes might not be
3
Extends longer than natural
as severely affected as other species in this guild
high
A steep rise in water levels will have negative effects because juvenile fish might get trapped in the
Duration is longer or shorter than
4
floodplains which will negatively affect recruitment
natural - i.e. hydrograph is
A longer rise will have relatively positive effects because juvenile fish will have more time to grow
high
Transition 1
steeper or shallower
and hence increase year class strength
Flows are more or less variable
Nil- the effects might be negligible because these are relatively small species which have relatively
5
medium
than natural
faster growth rates and extremely high turnover rates.
The effects may be negligible if synchronisation with rain is changed. However, the effects will be
Onset is earlier or later than
highly detrimental to silver catfish whose feeding ecology is closely tied to the rainy season where
6
natural ­ synchronisation with
high
rain may be changed
they feed voraciously on termites in the seasonally flooded floodplains
Flood season
Earlier onset might be positive while later may be negative
Higher floods for these floodplain fish might result in stronger year-class strength (and more than
Natural proportion of different
7
types of flood year changed
one cohort per season)
high
Lower floods will have a negative effect on fish production due to limited spawning/ breeding habitat
Onset is earlier or later than
Earlier onset may affect recruitment and will hence be negative to fish production
8
medium
natural
Later onset will be beneficial to fish production because of a prolonged growing season
Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on larval fish back-migrations into main channel
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
high
steeper or shallower






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EFA Botswana Fish

5.3.3 Fish Indicator 3 ­ Large fish migrating to floodplains

Table 0.3 Predicted response to possible changes in the flow regime of large fish migrating to floodplains in the Okavango River ecosystem
Confidence in
Question
number
Season
Possible flow change
Predicted response of indicator
prediction (very low,
low, medium, high)
Might be beneficial if later because it might result in a prolonged spawning season hence facilitating
Onset is earlier or later than
1
natural
increased fish production
High
Negative if earlier because then it shortens breeding season which might affect fish production
Dry Season
Water levels are higher or lower
Higher water levels might have a positive effect on fish production
2
Medium
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
3
Extends longer than natural
Negative because it might affect spawning/ breeding and feeding
medium
Duration is longer or shorter than
A steep rise in water levels will have negative effects because juvenile fish might get trapped in the
floodplains
4
natural - i.e. hydrograph is
A longer rise will have relatively positive effects because juvenile fish will have more time to grow
high
steeper or shallower
Transition 1
and hence increase year class strength
If the flows are highly variable, then this will have a negative effect on fish in this guild because they
5
Flows are more or less variable
take longer to respond to environmental variability which makes them more vulnerable to high
low
than natural
variability
Onset is earlier or later than
The effects may be negligible if synchronisation with rain is changed.
6
natural ­ synchronisation with
Earlier onset might be positive while later may be negative
medium
rain may be changed
Flood season
Higher floods for these floodplain fish might result in stronger year-class strength (and more than
7
Natural proportion of different
one cohort per season)
medium
types of flood year changed
Lower floods will have a negative effect on fish production due to limited spawning/ breeding habitat
Onset is earlier or later than
Earlier onset may affect recruitment and will hence be negative to fish production
8
medium
natural
Later onset will be beneficial to fish production because of a prolonged growing season
Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on larval fish back-migrations into main channel
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
high
steeper or shallower






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EFA Botswana Fish

5.3.4 Indicator 4 ­ Sandbank dwellers

Table 0.4 Predicted response to possible changes in the flow regime of sandbank dwellers in the Okavango River ecosystem
Confidence in
Question
Season
Possible flow change
Predicted response of indicator
prediction (very low,
number
low, medium, high)
Might be beneficial if later because it might result in a prolonged spawning season hence facilitating
1
Onset is earlier or later than
increased fish production
medium
natural
Negative if earlier because then it shortens breeding season which might affect fish production
Dry Season
Water levels are higher or lower
Higher water levels might be negative because they might erode habitat quality
2
Medium
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
3
Extends longer than natural
Negative because it might affect spawning/ breeding and feeding
medium
Duration is longer or shorter than
A steep rise in water levels will erode sandbanks and hence have a negative impact on habitat
4
quality
natural - i.e. hydrograph is
A longer rise will have relatively positive effects because juvenile fish will have more time to grow
medium
Transition 1
steeper or shallower
and hence increase year class strength
Flows are more or less variable
More variable flows than normal will have a negative impact on habitat quality which might affect fish
5
than natural
production
low
Onset is earlier or later than
The effects may be nil if synchronisation with rain is changed.
6
natural ­ synchronisation with
Earlier onset might be positive while later may be negative
medium
rain may be changed
Flood season
Higher floods may affect development of sandbank which will have a negative impact on fish
7
Natural proportion of different
production while lower floods than normal may also affect habitat integrity and hence fish production medium
types of flood year changed

Onset is earlier or later than
Earlier onset may affect recruitment and will hence be negative to fish production
8
natural
Later onset will be beneficial to fish production because of a prolonged growing season
medium
Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on sandbank habitats
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
high
steeper or shallower







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EFA Botswana Fish

5.3.5 Indicator 5 ­ Marginal vegetation dwellers

Table 0.5 Predicted response to possible changes in the flow regime of sandbank dwellers in the Okavango River ecosystem
Confidence in
Question
Season
Possible flow change
Predicted response of indicator
prediction (very low,
number
low, medium, high)
Onset is earlier or later than
Relatively negligible if later because it might result in a prolonged spawning season which is good
1
natural
Negative if earlier because then it shortens breeding season which might affect recruitment
High
Dry Season
Water levels are higher or lower
Higher water levels might have a negative effect because it will affect habitat integrity
2
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
medium
3
Extends longer than natural
Negative because it might affect spawning/ breeding and feeding
High
Duration is longer or shorter than
A steep rise in water levels will have negative effects
4
natural - i.e. hydrograph is
A shallower rise will have relatively positive effects
medium
Transition 1
steeper or shallower
5
Flows are more or less variable
The effects might be negligible - Nil
low
than natural
Onset is earlier or later than
Nil- The effects may be negligible if synchronisation with rain is changed.
6
natural ­ synchronisation with
Earlier onset might be positive while later may be negative
medium
Flood season
rain may be changed
Natural proportion of different
Higher floods than normal might be negative because this will affect habitat integrity
7
medium
types of flood year changed
Lower floods than normal might also affect habitat integrity negatively
Earlier decrease may affect fish recruitment negatively
8
Onset is earlier or later than
Late decrease may affect fish recruitment positively
medium
natural

Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on larval fish back-migrations into main channel
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
medium
steeper or shallower







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EFA Botswana Fish

5.3.6 Indicator 6 ­ backwater dwellers


Table 0.6 Predicted response to possible changes in the flow regime of backwater dwellers in the Okavango River ecosystem
Confidence in
Question
Season
Possible flow change
Predicted response of indicator
prediction (very low,
number
low, medium, high)
Onset is earlier or later than
Relatively negligible if later because it might result in a prolonged spawning season which is good
1
High
natural
Negative if earlier because then it shortens breeding season which might affect recruitment
Dry Season
Water levels are higher or lower
Higher water levels might have a positive effect
2
than natural
Lower water levels might have a negative effect because it might affect spawning/ breeding
High
3
Extends longer than natural
Negative because it might affect spawning/ breeding and feeding
High
Duration is longer or shorter than
A steep rise in water levels will have negative effects
4
natural - i.e. hydrograph is
A shallower rise will have relatively positive effects
medium
Transition 1
steeper or shallower
5
Flows are more or less variable
The effects might be negligible - Nil
low
than natural
Onset is earlier or later than
Nil - The effects may be negligible if synchronisation with rain is changed.
6
natural ­ synchronisation with
Earlier onset might be positive while later may be negative
medium
Flood season
rain may be changed
Natural proportion of different
Higher floods than normal are always good for general floodplain fish production
7
medium
types of flood year changed
Lower floods than normal are always negative for general floodplain fish production
Earlier decrease may affect fish recruitment negatively
Onset is earlier or later than
8
natural
Late decrease may affect fish recruitment positively
high

Transition 2
Duration is longer or shorter than
A steep hydrograph might have a negative effect on larval fish back-migrations into main channel
9
natural ­ i.e. hydrograph is
A shallower hydrograph might be beneficial to larval fish growth and eventual recruitment
medium
steeper or shallower


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EFA Botswana Fish

4.12 Conclusion
This study is a preliminary EFA of the Okavango Delta using several water
development scenarios and predicting their impacts on the Delta's fish stocks. The
results from this study were generally plausible despite a lack of comprehensive
relevant data. While extensive research has been done in the Delta's fish stocks,
most of this research focused either on ecological/ biological aspects or management
aspects of the fishery. This study highlighted the lack of habitat specific research,
with particular reference to the role of seasonal flooding on fish biology and ecology.
One major recommendation from this study therefore, is to initiate a comprehensive
study that established a quantitative relationship between the seasonal flood pulse
and various aspects of fish population dynamics in the Delta. Furthermore, some of
the indicators used in this study need to be re-defined reformulated because they are
not very clear. Indicators 2 and 3 in this sense can still be integrated as one indicator
of species that migrate into floodplains. The basic challenges of grouping the Delta's
species into specific guilds based on habitat requirements many. This is based on
the observation that most of the Delta's fish species utilize various habitats at
different stages of their life history stages. It is therefore a fallacy to simply categorize
H. vittatus as a channel dweller when its juveniles utilize shallow, littoral and well
vegetated parts of the Delta system. Moreover, H. vittatus is also known to occupy
large lagoons in the Delta which suggests that they are not necessarily restricted to
one particular habitat. There are other ubiquitous species in the Delta such as the
Clarias spp. (especially Clarias gariepinus) which are also not easy to group into any
particular habitat. Notwithstanding these pitfalls, the objectives of the study were
achieved and further research can help to clarify some of these knowledge gaps and
pitfalls.


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EFA Botswana Fish

5
FLOW-RESPONSE RELATIONSHIPS FOR USE IN
THE OKAVANGO EF-DSS
Response curves for fish using the three water development scenarios were
developed during a Knowledge Capture Workshop held in Windhoek, Namibia from
March 30 to April 4, 2009. The curves developed will be included in a CD of data that
accompanies this report.



6 REFERENCES
Relevant own work

Kgathi, D.L., Mmopelwa, G and Mosepele, K. 2005. Natural Resource Assessment in
the Okavango delta, Botswana; Case Studies of Some Key Resources. Natural
Resource Forum, 29: 70 - 81.

Lindholm, M., Hessen, D.O., Mosepele, K and Wolski, P., 2007. Flooding size and
energy pathways on a floodplain of the Okavango Delta. Wetlands, 27 (4): 775­784
Mmopelwa, G., Segametse, R. & Mosepele, K. (2005) Cost benefit analysis of
commercial fishing in Shakawe, Ngamiland, Botswana. Botswana Notes and
Records. 37, 11­19.

Mosepele K, Basimane O,Mosepele B, Thethela B. 2005. Using population
parameters to separate fish stocks in the Okavango Delta fishery, Botswana: A
preliminary assessment. Botswana Notes and Records 37: 292­305.

Mosepele K, Mosepele B. 2005. Spatial and temporal variability in fishery and fish
community structure in the Okavango Delta, Botswana: Implications towards fisheries
management. Botswana Notes and Records 37: 280­291

Mosepele, K and Kolding, J., 2003. Fish Stock Assessment in the Okavango delta,
Botswana ­ preliminary results from a length based analysis, pp 363 ­ 390. In
Bernard, T, Mosepele, K and Ramberg, L (Editors). Environmental Monitoring of
Tropical and Subtropical Wetlands. University of Botswana, Maun and University of
Florida, Gainesville, FLA.

Mosepele, K and Nengu, S., 2003. Growth, mortality, maturity and length-weight
parameters of selected fishes from the Okavango Delta, Botswana, p. 67-74. In D.
Pauly, B. Diouf, B.Samb, M.J. Vakily and M.L.D. Palamores (Editors). Fish
Biodiversity: Local Studies as Basis for Global Inferences. ACP-EU Fisheries
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Mosepele, K., 2000. Preliminary length based stock assessment of the main
exploited stocks of the Okavango delta fishery. Bergen, Norway, University of
Bergen, MPhil Thesis, 139 p.

Mosepele, K., 2008. Flood pulse in a subtropical floodplain fishery and the
consequences for steady state management, pages 56 ­ 62. In Totolo, O (Editor).
Proceedings of the 2nd IASTED Conference on Water Resource Management;
Science and technology innovation for sustainable development. Calgary, Canada.

Mosepele, K., Mmopelwa, G, Mosepele, B and Kgathi, D. L., 2007. Indigenous
knowledge and fish utilization in the Okavango Delta, Botswana: Implications for food
security, pages 292 - 302. In Ahmed, A (Editor). World Association for Sustainable
Development; Managing knowledge, technology and development in the era of
information revolution. Griffith University, Australia.

Mosepele, K., Mmopelwa, T.G. and Mosepele, B. (2003) Characterization and
monitoring of the Okavango delta artisanal fishery. In: Environmental Monitoring of
Tropical and Subtropical Wetlands (Eds T. Bernard, K. Mosepele and L. Ramberg).
University of Botswana, Maun and University of Florida, Gainesville, FLA.

Mosepele, K., Moyle, P.B., Glen, M.S., Purkey, D.R and Mosepele, B., 2009. Fish,
floods and ecosystem engineers: Aquatic conservation in the Okavango Delta,
Botswana. Bioscience, 59 (1): 53 ­ 64

Mosepele, K., Ngwenya, B.N and Bernard, T., 2006. Artisanal fishing and food
security in the Okavango Delta, Botswana, pages 159 ­ 168. In Ahmed, A (Editor).
World Sustainable Development Outlook; Global and local resources in achieving
sustainable development. (Interdescience Publishers: Geneva, Switzerland).

Ngwenya, B., and Mosepele, K. 2007. HIV/ AIDS, artisanal fishing and food security
in the Okavango Delta, Botswana. Physics and Chemistry of the Earth, 32: 1339­
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FAO Fishery resources and environment division, Rome, Italy.


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APPENDIX A: FULL DESCRIPTIONS OF INDICATORS

Ind.
Indicator Angola
1
Angola
Angola
Namibia
Namibia
Botswana
Botswana
Botswana
no.
2
3
4
5
6
7
8
1
Resident
Hydrocynus vittatus

H. vittatus,
S. robustus, S. giardi
channel and

S.altus
lagoon
H. vittatus, Labeo
dwellers,
lunatus
which also
undergo
longitudinal
migrations
2
Small
Tilapia rendalli,
Tilapia rendalli,
M. macrolepidotus, Schilbe intermedius
species that
Oreochromis
Clarias gariepinus
undertake
spp., Clarias spp.
lateral
migrations
into
seasonally
flooded
floodplains
as major
part of their
life history
strategy
3
Large
x x
x
T. rendalli, Oreochromis spp.,
species that
Serranochromis spp., C. gariepinus
undertake
lateral
migrations
into
seasonally
flooded
floodplains
as major
part of their
life history
strategy
4
Rock
x x
Labeo cylindricus, Chiloglanis
x
x x
dwellers
fasciatus, Amphilius uranoscopus
5
Marginal
Barbus
Synodontis
Aplocheilichthys
P.castelnaui, S.nigromaculatus, S.
vegetation
bifrenatus,
nigromaculatus
johnstonii, A. hutereaui,
carlottae Ctenopoma multispine, S.
dwellers of
Barbus radiatus,
Juvenile Sargochromis
macrocephalus, Hepsetus odoe,
the main
Pollimyrus
spp, Marcusenius

channel and
castelnaui,
macrolepidotus, Barbus
floodplain
Synodontis
radiatus
lagoons
nigromaculatus,
Serranochromis
angusticeps.

6
Sandbank
x x
x
Barbus unitaeniatus,
B.lateralis, B.poechii, Leptoglanis dorae cf
specialists
Brycinus lateralis

(Species
that prefer
clear, slow-
flowing or
quiet, well
vegetated
water in the
main
channel)

7
Shallow,
Barbus
x x
Aplocheilichtys spp,
Aplocheillichthys spp, B.afrovernayi,
well
afrovernayi,
Barbus paludinosus, B.
B.multilineatus, P. philander, H.elongatus,
vegetated
Pharyngochromis
multilineatus, T.
T.sparrmanii, P.acuticeps, B. Paludinosus,
backwater
acuticeps,
sparrmanii Pollimyrus
Microctenopoma intermediumi
habitats
Hemichromis
castelnaui
elongatus, Tilapia
sparrmanii.



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EFA Botswana Fish



The Okavango River Basin Transboundary Diagnostic Analysis Technical Reports

I
Diagnostic Analysis to establish a base of available
n 1994, the three riparian countries of the Okavango
scientific evidence to guide future decision making.
River Basin ­ Angola, Botswana and Namibia ­ agreed
The study, created from inputs from multi-disciplinary
to plan for collaborative management of the natural
teams in each country, with specialists in hydrology,
resources of the Okavango, forming the Permanent
hydraulics, channel form, water quality, vegetation,
Okavango River Basin Water Commission (OKACOM).
aquatic invertebrates, fish, birds, river-dependent
In 2003, with funding from the Global Environment
terrestrial wildlife, resource economics and socio-
Facility, OKACOM launched the Environmental
cultural issues, was coordinated and managed by a
Protection and Sustainable Management of the
group of specialists from the southern African region
Okavango River Basin (EPSMO) Project to coordinate
in 2008 and 2009.
development and to anticipate and address threats to

the river and the associated communities and
The following specialist technical reports were
environment. Implemented by the United Nations
produced as part of this process and form
Development Program and executed by the United
substantive background content for the Okavango
Nations Food and Agriculture Organization, the project
River Basin Trans-boundary Diagnostic Analysis
produced the Transboundary.

Final Study
Reports integrating findings from all country and background reports, and covering the entire
Reports
basin.


Aylward, B.
Economic Valuation of Basin Resources: Final Report to
EPSMO Project of the UN Food & Agriculture Organization as
an Input to the Okavango River Basin Transboundary
Diagnostic Analysis


Barnes, J. et al.
Okavango River Basin Transboundary Diagnostic Analysis:
Socio-Economic Assessment Final Report


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment Project
C.A.
Initiation Report (Report No: 01/2009)


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment EFA
C.A.
Process Report (Report No: 02/2009)


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment
C.A.
Guidelines for Data Collection, Analysis and Scenario Creation
(Report No: 03/2009)

Bethune,
S.
Mazvimavi,
Okavango River Basin Environmental Flow Assessment
D. and Quintino, M.
Delineation Report (Report No: 04/2009)


Beuster, H.
Okavango River Basin Environmental Flow Assessment
Hydrology Report: Data And Models(Report No: 05/2009)

Beuster,
H. Okavango River Basin Environmental Flow Assessment
Scenario Report : Hydrology (Report No: 06/2009)


Jones, M.J.
The Groundwater Hydrology of The Okavango Basin (FAO
Internal Report, April 2010)


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment
C.A.
Scenario Report: Ecological and Social Predictions (Volume 1
of 4)(Report No. 07/2009)


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment
C.A.
Scenario Report: Ecological and Social Predictions (Volume 2
of 4: Indicator results) (Report No. 07/2009)


King, J.M. and Brown,
Okavango River Basin Environmental Flow Assessment
C.A.
Scenario Report: Ecological and Social Predictions: Climate
Change Scenarios (Volume 3 of 4) (Report No. 07/2009)


King, J., Brown, C.A.,
Okavango River Basin Environmental Flow Assessment
Joubert, A.R. and
Scenario Report: Biophysical Predictions (Volume 4 of 4:
Barnes, J.
Climate Change Indicator Results) (Report No: 07/2009)


King, J., Brown, C.A.
Okavango River Basin Environmental Flow Assessment Project
and Barnes, J.
Final Report (Report No: 08/2009)


Malzbender, D.
Environmental Protection And Sustainable Management Of The
Okavango River Basin (EPSMO): Governance Review


Vanderpost, C. and
Database and GIS design for an expanded Okavango Basin
Dhliwayo, M.
Information System (OBIS)


Veríssimo, Luis
GIS Database for the Environment Protection and Sustainable
Management of the Okavango River Basin Project

Wolski,
P.
Assessment of hydrological effects of climate change in the
Okavango Basin





45

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EFA Botswana Fish

Country Reports
Angola
Andrade e Sousa,
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Biophysical Series
Helder André de
Okavango: Módulo do Caudal Ambiental: Relatório do
Especialista: País: Angola: Disciplina: Sedimentologia &
Geomorfologia


Gomes, Amândio
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Okavango: Módulo do Caudal Ambiental: Relatório do
Especialista: País: Angola: Disciplina: Vegetação

Gomes,
Amândio
Análise Técnica, Biofísica e Socio-Económica do Lado
Angolano da Bacia Hidrográfica do Rio Cubango: Relatório
Final:Vegetação da Parte Angolana da Bacia Hidrográfica Do
Rio Cubango


Livramento, Filomena
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Okavango: Módulo do Caudal Ambiental: Relatório do
Especialista: País: Angola: Disciplina:Macroinvertebrados


Miguel, Gabriel Luís
Análise Técnica, Biofísica E Sócio-Económica do Lado
Angolano da Bacia Hidrográfica do Rio Cubango:
Subsídio Para o Conhecimento Hidrogeológico
Relatório de Hidrogeologia


Morais, Miguel
Análise Diagnóstica Transfronteiriça da Bacia do Análise Rio
Cubango (Okavango): Módulo da Avaliação do Caudal
Ambiental: Relatório do Especialista País: Angola Disciplina:
Ictiofauna

Morais,
Miguel
Análise Técnica, Biófisica e Sócio-Económica do Lado
Angolano da Bacia Hidrográfica do Rio Cubango: Relatório
Final: Peixes e Pesca Fluvial da Bacia do Okavango em Angola


Pereira, Maria João
Qualidade da Água, no Lado Angolano da Bacia Hidrográfica
do Rio Cubango

Santos,
Carmen
Ivelize
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Van-Dúnem S. N.
Okavango: Módulo do Caudal Ambiental: Relatório de
Especialidade: Angola: Vida Selvagem


Santos, Carmen Ivelize
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Van-Dúnem S.N.
Okavango:Módulo Avaliação do Caudal Ambiental: Relatório de
Especialidade: Angola: Aves

Botswana Bonyongo, M.C.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report: Country:
Botswana: Discipline: Wildlife


Hancock, P.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module : Specialist Report: Country:
Botswana: Discipline: Birds

Mosepele,
K. Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report: Country:
Botswana: Discipline: Fish


Mosepele, B. and
Okavango River Basin Technical Diagnostic Analysis:
Dallas, Helen
Environmental Flow Module: Specialist Report: Country:
Botswana: Discipline: Aquatic Macro Invertebrates

Namibia
Collin Christian &
Okavango River Basin: Transboundary Diagnostic Analysis
Associates CC
Project: Environmental Flow Assessment Module:
Geomorphology


Curtis, B.A.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report Country:
Namibia Discipline: Vegetation


Bethune, S.
Environmental Protection and Sustainable Management of the
Okavango River Basin (EPSMO): Transboundary Diagnostic
Analysis: Basin Ecosystems Report


Nakanwe, S.N.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report: Country:
Namibia: Discipline: Aquatic Macro Invertebrates

Paxton,
M. Okavango River Basin Transboundary Diagnostic Analysis:
Environmental Flow Module: Specialist
Report:Country:Namibia: Discipline: Birds (Avifauna)


Roberts, K.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report: Country:
Namibia: Discipline: Wildlife

Waal,
B.V. Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module: Specialist Report: Country:
Namibia:Discipline: Fish Life
Country Reports
Angola
Gomes, Joaquim
Análise Técnica dos Aspectos Relacionados com o Potencial
Socioeconomic
Duarte
de Irrigação no Lado Angolano da Bacia Hidrográfica do Rio
Series
Cubango: Relatório Final

Mendelsohn,
.J.
Land use in Kavango: Past, Present and Future


Pereira, Maria João
Análise Diagnóstica Transfronteiriça da Bacia do Rio
Okavango: Módulo do Caudal Ambiental: Relatório do
Especialista: País: Angola: Disciplina: Qualidade da Água

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EFA Botswana Fish



Saraiva, Rute et al.
Diagnóstico Transfronteiriço Bacia do Okavango: Análise
Socioeconómica Angola

Botswana Chimbari, M. and
Okavango River Basin Trans-Boundary Diagnostic Assessment
Magole, Lapologang
(TDA): Botswana Component: Partial Report: Key Public Health
Issues in the Okavango Basin, Botswana

Magole,
Lapologang
Transboundary Diagnostic Analysis of the Botswana Portion of
the Okavango River Basin: Land Use Planning


Magole, Lapologang
Transboundary Diagnostic Analysis (TDA) of the Botswana p
Portion of the Okavango River Basin: Stakeholder Involvement
in the ODMP and its Relevance to the TDA Process

Masamba,
W.R.
Transboundary Diagnostic Analysis of the Botswana Portion of
the Okavango River Basin: Output 4: Water Supply and
Sanitation


Masamba,W.R.
Transboundary Diagnostic Analysis of the Botswana Portion of
the Okavango River Basin: Irrigation Development

Mbaiwa.J.E. Transboundary Diagnostic Analysis of the Okavango River
Basin: the Status of Tourism Development in the Okavango
Delta: Botswana


Mbaiwa.J.E. &
Assessing the Impact of Climate Change on Tourism Activities
Mmopelwa, G.
and their Economic Benefits in the Okavango Delta

Mmopelwa,
G.
Okavango River Basin Trans-boundary Diagnostic Assessment:
Botswana Component: Output 5: Socio-Economic Profile


Ngwenya, B.N.
Final Report: A Socio-Economic Profile of River Resources and
HIV and AIDS in the Okavango Basin: Botswana

Vanderpost,
C.
Assessment of Existing Social Services and Projected Growth
in the Context of the Transboundary Diagnostic Analysis of the
Botswana Portion of the Okavango River Basin

Namibia
Barnes, J and
Okavango River Basin Technical Diagnostic Analysis:
Wamunyima, D
Environmental Flow Module: Specialist Report:
Country: Namibia: Discipline: Socio-economics


Collin Christian &
Technical Report on Hydro-electric Power Development in the
Associates CC
Namibian Section of the Okavango River Basin


Liebenberg, J.P.
Technical Report on Irrigation Development in the Namibia
Section of the Okavango River Basin


Ortmann, Cynthia L.
Okavango River Basin Technical Diagnostic Analysis:
Environmental Flow Module : Specialist Report Country:
Namibia: discipline: Water Quality


Nashipili,
Okavango River Basin Technical Diagnostic Analysis: Specialist
Ndinomwaameni
Report: Country: Namibia: Discipline: Water Supply and
Sanitation

Paxton,
C.
Transboundary Diagnostic Analysis: Specialist Report:
Discipline: Water Quality Requirements For Human Health in
the Okavango River Basin: Country: Namibia




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