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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

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



 

 

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