On the potential impact of harbour seal predation on the cod population in the eastern North Sea |
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| Institution: | 1. Department of Aquaculture, Faculty of Food Science and Fisheries, West Pomeranian University of Technology, Szczecin, Poland;2. Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, Kraków 30-059, Poland;3. Systems Research Institute, Polish Academy of Sciences, ul. Newelska 6, Warsaw 01–447, Poland;1. U.S. Geological Survey, Great Lakes Science Center, 1451 Green Rd, Ann Arbor, MI 48105, USA;2. Department of Environmental Sciences, University of Toledo, 2801 W. Bancroft, Toledo, OH 43606, USA;3. Michigan Department of Natural Resources, Alpena Fisheries Research Station, 160 E. Fletcher, Alpena, MI 49707, USA;4. U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, 2803, Jolly Rd, Okemos, MI 48864, USA;1. Royal Netherlands Institute for Sea Research (NIOZ), Postbus 59, 1790 AB Den Burg, The Netherlands;2. IMARES, Postbus 68, 1970 AB IJmuiden, The Netherlands |
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| Abstract: | Increasing Scandinavian harbour seal populations during the last decades coincide in time with the collapse of the cod fishery. Assumptions of a causal relationship have led to claims favouring re-introduction of seal hunting. Proposals for ‘adaptive management’ often assume that decimating seal populations will automatically favour the fishery. This argument presupposes seal predation to be sufficiently large to have a measurable impact on the fish population. The potential magnitude of the cod-seal interaction was analysed using data on harbour seal abundance, feeding habits and compiled information on cod life history and cod landing statistics. A size-structured life history matrix for the cod population was applied and the size-specific prey preferences of harbour seals were taken into account. Estimated seal predation was small compared to both the landings by the fishery, and to minimum estimates of the total cod population. Furthermore, since the size classes of cod targeted by seals have low reproductive values, the impact of seal predation on cod production will be further reduced. Our analyses suggest harbour seals have a negligible impact on the cod fishery. |
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