The
Linnean Society with The Malacological Society of London A joint
evening meeting at Burlington House, London
Cephalopod
Systematics, Ecology and Fisheries
Thursday 4 March
2004
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Detail from the painting
‘She finds a way through’ by Paul Rodhouse. |
Cephalopod
ecology and fisheries
Paul Rodhouse, British Antarctic Survey
Overfishing
is causing changes in global marine ecosystems including a downward
shift in the mean trophic level of exploited species. As groundfish
landings have decreased, landings of cephalopods, which are short-lived
trophic opportunists, have increased in some fisheries suggesting
overfishing of their predators and, or, competitors may have positively
affected cephalopod populations. These changes in marine ecosystems
emphasize the need for methods
analogous to satellite remote sensing of land use in agriculture.
The cephalopod fisheries, which are implicated in change, use powerful
incandescent lights. We used archived data from the United States
Defence Meteorological Satellite Programme (DMSP) Operational Linescan
System (OLS) to formulate a detailed description and interpretation
of the global light fishery in relation to physical and biological
oceanography. The extent of interaction between the
exploited squid and groundfish stocks, and between the target species
of the fisheries and higher predators, was then assessed. Globally,
the highest concentration of light fishing is in the Kuroshio Current,
the China Sea Shelves and Sunda-Arafura Shelves Provinces of east
Asia. Other major light fisheries are pursued around New Zealand,
in the California and Humboldt Currents and in the southwest Atlantic.
An analysis of the world squid catch based on FAO data
revealed that 63-89% of the total catch is caught with lights that
can be visualized with DMSP-OLS imagery. In three of the Provinces
where concentrations of light fishing vessels were located, increasing
cephalopod catches have coincided with overexploitation of groundfish
stocks. In two of these the squid catch is dominated by loliginids.
Evidence that overexploitation of groundfish is implicated in the
expansion of ommastrephid fisheries is less clear except
perhaps in New Zealand. The other ommastrephid fisheries are either
in areas dominated by pelagic fisheries or are off shelf. Given the
extent of light fishing in several of the ocean's ecological provinces,
and the potential for expansion into ecologically sensitive areas
such as the Antarctic, it is important to know what their direct and
indirect effects are on the functioning of marine ecosystems
The role of cannibalism in the trophic ecology and population
structure of cephalopods
Nadine M. Johnston, British Antarctic Survey
Cannibalism is a particular feature of cephalopod feeding biology and
has been recorded in ommastrephid and loliginid squid and is undoubtedly
important to natural mortality. To date, however, the nature of cannibalism
has not been systematically studied in squids and there is no consensus
on its importance. This study focuses on Illex argentinus and
Loligo gahi, which are the subject of large scale international
fisheries in the southwest Atlantic, and addresses
key aspects of their trophic ecology which are currently unknown. The
diets of I. argentinus and L. gahi are examined to
quantify the importance of cannibalism and the role these squid in the
marine food web of the southwest Atlantic. The work examines the impact
of cannibalism on the natural mortality of I. argentinus and
L. gahi, and considers ways in which this may affect population
dynamics. The influence of inter-annual variations in food availability
and population density on the extent of cannibalism in I. argentinus
and L. gahi is explored.
Ilex on deck
Cephalopod systematics, ecology and evolution
Louise Allcock, Queen’s University,
Belfast
Recent fishing opportunities around Elephant Island (South Shetland
Islands, Antarctic Peninsula) have led to the conclusion that there
are many more species of the endemic octopus genus Pareledone than
was previously though. Descriptions of seven new species of papillated
Pareledone are in review and it is likely that smooth skinned Pareledone
have radiated similarly. Unfortunately we lack good morphological
characters to investigate the smooth skinned group and questions on
their radiation can probably only be answered using molecular markers
such as microsatellites. Pareledone are also extremely abundant
around Elephant Island and we suspect that benthic octopods may have
expanded into a niche previously occupied by records of octopus abundance
pre-date the fishery so only a long term study of the relationship
between the fish and octopus stocks can confirm the theory. However,
such an ecological shift has been known to occur on other fishing
grounds following over exploitation. It has been noted during morphological
and preliminary molecular work that Pareledone and other
endemic Antarctic octopus genera are closely related to some of the
deep-sea fauna. We are proposing a model whereby an extinction event,
which might, for example, have been associated with past global climate
change and deep-ocean oxygen minima, allowed the subsequent colonisation
of the deep-sea by Antarctic fauna. We hope to use molecular techniques
to test this theory.
Much of this work has been undertaken in collaboration with Mike Vecchione,
Smithsonian Institute and Uwe Piatkowski, IFM, Kiel. The Alfred Wegener
Institute have provided extensive sea time aboard RV Polarstern.
Speakers and some members of the audience at the Cephalopod evening
at the Linnean Society
Above,
Below, L to R: Georges Dussart, David Reid, Suzanne Williams and John
Taylor;
Katrin Linse and Nadine Johnston.
Speakers
and some members of the audience at the Cephalodod evening at
the Linnean Society.
L to R:
Paul Rodhouse and Louise
Allcock; Noel and Solene Morris and
(centre) Liz Platts. |
|
Lto R:
Georges Dussart, David Reid, Suzanne Williams
and John Taylor. Katrin Linse and Nadine HJohnston |