|Effects of fisheries on the Cantabrian Sea shelf ecosystem|In: Ecological Modelling. Elsevier: Amsterdam; Lausanne; New York; Oxford; Shannon; Tokyo. ISSN 0304-3800, more
Collisions; Ecosystems; Fisheries; Food webs; Marine
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The Cantabrian Sea shelf ecosystem is described using a mass-balance model of trophic interactions, in order to understand theeffects of the different fisheries that operate in this area. The study was based on a database of bottom trawl surveys, ICES stockassessment working groups, stomach analyses, fisheries research and was supplemented by published information. The modelhad 28 trophic groups corresponding to pelagic, demersal and benthic domains, also including detritus and fishery discards. Theresults indicated that the biomass and production of some groups would be unrealistic if they were independently estimated bysingle-species assessment approaches. Summaries are given to illustrate the flow distributions between groups. Strong relationshipsexisted between the pelagic, demersal and benthic domains due to key groups, like zooplankton suprabenthic and horsemackerel, that transferred the flow from primary production to the upper trophic levels. Feeding pressure on phytoplankton waslow and detritivorous species were an important component of the ecosystem.Estimations of the trophic level of the fisheries, transfer efficiency between trophic levels and mixed trophic impact analysis,that consider the fishery both as an impacting and as an impacted component, were also included. The results indicated a fisheriesimpact level in the Cantabrian Sea comparable to that in the most intensively exploited temperate shelf ecosystems of the world.The fishery was operating at a mean trophic level of 3.7. The importance of discards as food in the ecosystem was low, incomparison with detritus, primary producers or other low trophic levels. The negative trophic impact of trawling on the differentgroups of the system was high and much stronger than the other gears studied. All fishing gears, except the purse seine, hadnegative impact on fish feeders and elasmobranchs. The mean trophic level of Cantabrian Sea fisheries declined from 1983 to1993 but has remained steady since then.