SEAMOUNTS AND PELAGIC
that an operational definition of
seamounts, and one that is partic-
FISHERIES INTERACTIONS
ularly relevant to pelagic fisheries,
should include underwater fea-
UNDER STUDY
tures less than 1000 m above the
sea floor, and having different
geologic features such as terraces,
ridges, banks, plateaux, and
In October 2005, SPC's Oceanic
Valerie Allain,
shelves.
Fisheries Programme, in collabo-
Fisheries Scientist
ration with the Forum Fisheries
(Ecosystem Analyst)
Only those seamounts that extend
Agency (FFA), started a five-year
Secretariat of the Pacific
up into the euphotic zone1
and
endeavor called the Pacific
Community
the lower level of the deep scatter-
Islands Oceanic Fisheries
(ValerieA@spc.int)
ing layer (DSL)2 will have an
Management Project (OFM proj-
influence on pelagic fish species.
ect). The OFM project is funded
by the Global Environment
the Pacific and future projects
How many seamounts
Facility (GEF), and the Scientific
under development. Afterwards,
are in the Pacific Ocean?
Assessment and Monitoring
many topics relating to
Enhancement Component of the
seamounts and pelagic fisheries
The number of potential
project (including ecosystem
were discussed, and some of
seamounts in the Pacific Ocean
analysis) is implemented by SPC.
these are summarized below.
could be 30,000, although less
than 1000 have been properly
One of the objectives of the OFM
What is a seamount?
identified and less than 150 have
project is to obtain an enhanced
been explored. There is a critical
understanding of the ecology of
A seamount is generally defined
need to gather accurate, fine-
seamounts, in particular their
as an isolated underwater moun-
scaled bathymetric data to prop-
influence on the aggregation and
tain that rises more than 1000 m
erly identify the seamounts.
movement of pelagic fish species,
above the seafloor. However,
Bathymetric data on the location
and also the impact of fisheries
workshop participants agreed
of seamounts comes from two
on seamount ecosystems.
To organise this specific activity, a
seamount research planning
workshop, gathering 14 seamount
and benthic and pelagic fisheries
experts, took place at SPC head-
quarters in Noumea on 20 and 21
March 2006.
The objective of this workshop
was to review existing knowl-
edge about seamounts in the
Pacific in relation to pelagic fish-
eries, and plan activities within
the timeframe of the OFM project
to gather more information on
the ecology of seamounts and
pelagic fisheries.
Three dimensional diagram of the Bear Seamount in the
Atlantic Ocean whose summit reaches about 1000 m depth
The workshop began with partic-
(source: National Oceanic and Atmospheric Administration:
ipants' presentations of work
http://www.oceanexplorer.noaa.gov/explorations/deepeast01/logs/
sep13/media/bear_seamount.html)
conducted around seamounts in
1 Sea surface waters where enough light penetrates for photosynthesis to occur (i.e. down to about 80 meters or more). The
depth of the euphotic zone varies with the water's extinction coefficient, angle of incidence of sunlight, length of day, and
cloudiness. (FishBase Glossary).
2 A horizontal zone of living organisms, usually schools of fish, occurring below the surface in many ocean areas. The zone
derives its name from the layer of water scatters or reflects sound waves, causing echoes in depth sounders. The DSL tends
to rise towards the surface at night, and to descend during daytime. (Encyclopedia Britannica; FishBase Glossary).
SPC Fisheries Newsletter #116 ­ January/March 2006 33

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SEAMOUNTS AND PELAGIC FISHERIES INTERACTIONS UNDER STUDY
stages of some species (e.g.
spawning grounds, feeding
grounds, nursery areas). Because
fish aggregate around seamounts,
they became a target for fisher-
men. Two examples of fisheries
that have developed around
seamounts include the tuna fish-
ery around Capricorn Seamount
in Tonga, and Cross Seamount in
Hawaii. Already some dramatic
depletion of resident fish popula-
tions around seamounts has been
observed (e.g. the swordfish fish-
ery around Brittania Seamount in
Australia).
Do pelagic fisheries have an
impact on seamounts?
Position of potential seamounts based on analysis of 2-minute
gridded global relief (ETOPO2) satellite data.
Seamounts are very fragile and
Data from Kitchingman A. and Lai S 2004. Inferences on
specific ecosystems mainly
potential seamount locations from mid-resolution bathymetric unknown but characterized by a
data. Fisheries Centre Research Reports. 12(5):7­12.
very particular fauna. Each time
major sources: ship-derived data
Capricorn Seamount in Tonga,
a new seamount is explored, a
and satellite-derived data.
for example, is a particularly pro-
high percentage of the species
ductive fishing area.
collected are new to science, and
Ship-derived data are generally
the fauna often show a high
very detailed and are of high reso-
A commonly stated hypothesis
degree of endemism4. Hence,
lution, but these data only cover
to explain the aggregation of
seamounts constitute ecosystems
small oceanographic areas. These
pelagic fish around seamounts is
of very special interest for con-
kinds of data allows for locating
the unique water circulation
servation and it is important to
seamounts, but can also provide
around seamounts, and the exis-
evaluate the impact of human
very detailed topographic maps of
tence of enhanced phytoplank-
activities on them in order to pre-
seamounts. Satellite-derived data
ton production3, which in turn
vent destruction and damage to
provide the potential location of
supports a rich ecosystem. Large
these poorly known and unex-
seamounts, offering complete cov-
numbers of small fish, crus-
plored features.
erage of an ocean. Resolution
taceans, and squids feeding on
depends on the dataset used, but
large quantities of phytoplank-
Heavy bottom trawling fishing
no detailed topographic informa-
ton and zooplankton will attract
gear dragged on the top or on the
tion on seamounts is available.
pelagic fish such as tuna.
slopes of seamounts can cause
Considerable work is still required
However, the enhanced produc-
significant damages to seamount
to obtain an accurate and precise
tion hypothesis has not been
fauna. However, some pelagic
list of seamounts in the Pacific
observed in many explored
fisheries (e.g. purse seine, long-
Ocean.
seamounts. A new idea is that the
line) are operated from the sur-
DSL is trapped by seamounts
face, and if the lines hang above
What is the influence of
and will act as the feeding
the seamount (i.e. they do not
seamounts on pelagic
source, thus attracting predatory
touch it), it is suspected that
species and fisheries?
species.
pelagic fisheries in surface waters
are unlikely to impact the fauna
Fishermen are well aware that
Seamounts probably have differ-
living directly below on the
seamounts attract pelagic fish;
ent roles for different life-history
seamounts. But, removing large
3 A flora of freely floating, often minute organisms that drift with water currents. Like vegetation, phytoplankton uses carbon
dioxide, releases oxygen, and converts minerals to a form that animals can use when feeding on phytoplankton.
Phytoplankton constitute the base of the food chain, and are consumed by zooplankton that are in turn consumed by small
fish that constitute the food of larger fish. (Encyclopedia Britannica).
4 A species whose distribution is confined to a given area is said to be endemic to that area. For example, some particular
species of sponges or crabs are only found on a specific seamount, therefore, they are said to be endemic to this seamount
and not found anywhere else.
34 SPC Fisheries Newsletter #116 ­ January/March 2006

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SEAMOUNTS AND PELAGIC FISHERIES INTERACTIONS UNDER STUDY
quantities of pelagic predators
there are data from onboard
The Papua New Guinea (PNG)
could cause disequilibrium of the
observers for a small percentage
tagging project will focus on the
ecosystem around seamounts.
of the fleet. These data are on a
Bismarck Sea/Solomon Seas and
much finer scale and include
adjacent areas, and will visit
The general lack of knowledge
bycatch species composition. The
some seamounts. This is the first
about seamount ecosystems (loca-
OFM project will try to determine
phase of a larger regional tuna
tion, and geological, biological,
if there is any apparent connec-
tagging project, and one of the
oceanographical characteristics)
tion between fisheries data (catch
objectives is to tag tunas around
shows the importance of imple-
per unit of effort, species compo-
seamounts to investigate the
menting studies on their ecology
sition, size of fish caught) and
behaviour of fish and their site
to acquire a better understanding
seamount presence/absence or
fidelity. Biological sampling, par-
of their potential impact on pelag-
other characteristics. Datasets
ticularly of stomach contents,
ic fisheries and vice versa.
from previous large-scale tagging
will be carried out during the
programmes will also be
tagging cruises to gain a better
Analysing existing data
reanalysed to investigate whether
understanding of the trophic
there is any obvious site fidelity
impact of seamounts on the fish.
The OFM project's first task will
for fish tagged in the vicinity of
be to obtain an accurate list of
seamounts.
The Seamount Planning Work-
seamounts. This will be done by
shop allowed experts to share
reanalysing the Kitchingman and
Acquiring new data
their views on the ecology of
Lai dataset to remove any false
seamounts and to plan research
identification of seamounts and
In addition to analysing existing
efforts for the coming years.
to identify submarine banks rele-
data, new field work will be
Another meeting will be organ-
vant to fisheries.
undertaken during the OFM
ised in two to three years' time to
project to enhance our under-
review the work undertaken
This dataset of seamounts will be
standing of seamount ecosys-
thus far, and future studies to be
examined in reference to fisheries
tems in relation to pelagic fish-
undertaken.
catch and effort data provided by
eries. Several sampling cruises
SPC member countries and dis-
are already planned for the first
tant water fishing nations, and
part of the project.
compiled by SPC's Oceanic Fish-
eries Programme. In addition,
Catch per unit of effort (CPUE in kg per 100 hooks) of the longline tuna catch in 2002 per 1
degree square. Black triangles represent potential seamounts whose summits are between 50 and
1000 m depth. In the circle is shown the high catches around Capricorn Seamount.
Data from SPC's Oceanic Fisheries Programme.
SPC Fisheries Newsletter #116 ­ January/March 2006 35

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