Effects of fisheries on the Cantabrian Sea shelf ecosystem

Abstract The Cantabrian Sea shelf ecosystem is described using a mass-balance model of trophic interactions, in order to understand the effects of the different fisheries that operate in this area. The study was based on a database of bottom trawl surveys, ICES stock assessment working groups, stomach analyses, fisheries research and was supplemented by published information. The model had 28 trophic groups corresponding to pelagic, demersal and benthic domains, also including detritus and fishery discards. The results indicated that the biomass and production of some groups would be unrealistic if they were independently estimated by single-species assessment approaches. Summaries are given to illustrate the flow distributions between groups. Strong relationships existed between the pelagic, demersal and benthic domains due to key groups, like zooplankton suprabenthic and horse mackerel, that transferred the flow from primary production to the upper trophic levels. Feeding pressure on phytoplankton was low 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 fisheries impact 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, in comparison with detritus, primary producers or other low trophic levels. The negative trophic impact of trawling on the different groups of the system was high and much stronger than the other gears studied. All fishing gears, except the purse seine, had negative impact on fish feeders and elasmobranchs. The mean trophic level of Cantabrian Sea fisheries declined from 1983 to 1993 but has remained steady since then.

[1]  Á. Guerra,et al.  Predatory Relationships of Two Sympatric Squid, Todaropsis Eblanae And Illex Coindetii (Cephalopoda: Ommastrephidae) in Galician Waters , 1996, Journal of the Marine Biological Association of the United Kingdom.

[2]  J. Polovina,et al.  I. The ECOPATH Model and Its Application to French Frigate Shoals , 1984 .

[3]  F. Sánchez,et al.  ICES CM 2001 / N : 06 SURVIVAL OF LESSER SPOTTED DOGFISH ( Scyliorhinus canicula , L . ) DISCARDED BY TRAWLERS , 2001 .

[4]  L. Valdés,et al.  Time-series analysis of copepod diversity and species richness in the southern Bay of Biscay off Santander, Spain, in relation to environmental conditions , 1998 .

[5]  R. Furness,et al.  Consumption of discards by seabirds in the North Sea , 1995 .

[6]  J. Gil,et al.  Hydrographic mesoscale structures and Poleward Current as a determinant of hake (Merluccius merluccius) recruitment in southern Bay of Biscay , 2000 .

[7]  I. Barannikova.  Sex steroids in the serum of Caspian sturgeons and their specific cytosol binding in brain and gonads during the migratory cycle , 1999 .

[8]  Villy Christensen,et al.  Trophic models of aquatic ecosystems , 1993 .

[9]  H. González,et al.  Diet of the gelatinous zooplankton in Hardangerfjord (Norway) and potential predatory impact by Aglantha digitale (Trachymedusae) , 1996 .

[10]  C. S. Holling.  Resilience and Stability of Ecological Systems , 1973 .

[11]  E. Pianka.  The structure of lizard communities , 1973 .

[12]  F. S. Delgado.  Las comunidades de peces de la plataforma del Cantábrico , 1993 .

[13]  F. Rocha,et al.  The diets of Loligo vulgaris and L. forbesi (Cephalopoda: Loliginidae) in northwestern Spanish Atlantic waters , 1994 .

[14]  A. Uriarte,et al.  Descartes de la flota española en el área del ICES , 1996 .

[15]  R. Anadón,et al.  Ingestion rates of phytoplankton by copepod size fractions on a bloom associated with an off-shelf front off NW Spain , 1998 .

[16]  Francisco Arreguín Sánchez,et al.  survival of small-spotted catshark (scyliorhinus canicula) discarded by trawlers in the cantabrian sea , 2005, Journal of the Marine Biological Association of the United Kingdom.

[17]  F. Velasco,et al.  Importance of discarded blue whiting (Micromesistius poutassou) in the diet of lesser spotted dogfish (Scyliorhinus canicula) in the Cantabrian Sea , 1998 .

[18]  I. Palomera,et al.  Trophic ecology of the European anchovy , 2006 .

[19]  P. Abaunza,et al.  Distribution and age structure of mackerel (Scomber scombrus, L.) and horse mackerel (Trachurus trachurus, L.) in the northern coast of Spain, 1989-1994 , 1997 .

[20]  D. Pauly,et al.  Primary production required to sustain global fisheries , 1995, Nature.

[21]  F. Velasco,et al.  The feeding behaviour of some demersal fish species in response to artificial discarding , 2002 .

[22]  Stefan Garthe,et al.  Amounts of discards by commercial fisheries and their significance as food for seabirds in the North Sea , 1996 .

[23]  John J. Walsh,et al.  Death in the sea: Enigmatic phytoplankton losses , 1983 .

[24]  J. L. Cort.  Biología y pesca del atún rojo, thunnus thynnus (l.), del Mar Cantábrico , 1990 .

[25]  L. I. Olaso-Toca,et al.  The diet of the horse mackerel, Trachurus trachurus (Linnaeus 1758), in the Cantabrian Sea (north of Spain) , 1999 .

[26]  V. Christensen.  Ecosystem maturity - towards quantification , 1995 .

[27]  R. Putman.  Food and Feeding Behaviour of Domestic Stock , 1986 .

[28]  Villy Christensen,et al.  On Steady-State Modelling of Ecosystems* , 1993 .

[29]  E. Odum.  The strategy of ecosystem development. , 1969, Science.

[30]  R. Anadón,et al.  Evidence of heavy predation by Noctiluca scintillans on Acartia clausi (Copepoda) eggs off the centr , 1999 .

[31]  Villy Christensen,et al.  ECOPATH II − a software for balancing steady-state ecosystem models and calculating network characteristics , 1992 .

[32]  Carl J. Walters,et al.  Ecopath, Ecosim, and Ecospace as tools for evaluating ecosystem impact of fisheries , 2000 .

[33]  E. Marañón,et al.  Phytoplankton biomass and production in shelf waters off NW Spain: spatial and seasonal variability in relation to upwelling , 1996, Hydrobiologia.

[34]  Juan Freire.  Feeding ecology of Liocarcinus depurator (Decapoda: Portunidae) in the Ria de Arousa (Galicia, north-west Spain): effects of habitat, season and life history , 1996 .

[35]  U. Båmstedt,et al.  Euphausiid predation on copepods in coastal waters of the Northeast Atlantic , 1998 .

[36]  D. Pauly,et al.  Fishing down marine food webs , 1998, Science.