☆ 4.5 Article Proceedings Paper

The role of pelagic fish as forage for the demersal fish community in the southern Bay of Biscay

JOURNAL OF MARINE SYSTEMS (2008)

Journal

JOURNAL OF MARINE SYSTEMS

Volume 72, Issue 1-4, Pages 407-417

Publisher

ELSEVIER SCIENCE BV

DOI: 10.1016/j.jmarsys.2007.04.007

Keywords

trophic relationships; stomach contents; pelagic fish; demersal fish; prey availability; Bay of Biscay

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Protocol

Community support

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Abstract

The small pelagic fish represents the link between nekton and demersal communities, and they are an important food source for some demersal fish species. In the autumns between 1993 and 2002, 74,869 stomach contents of 25 demersal fish species were analysed during the scientific surveys organized by the Instituto Espanol de Oceanografia. These species represent the demersal fish community of the southern Bay of Biscay. An important part of their diet (39% by volume) was composed of pelagic fish species (e.g. Engraulis encrasicolus, Gadiculus argenteus, Micromesistius poutassou, Trachurus trachurus, Sardina pilchardus, Scomber scombrus). Among all these prey species, the relevance of M. poutassou and G. argenteus stood out because of their high abundance both in the diets and during the scientific surveys. The relevance of pelagic fish as prey increased with predator size, reaching more than 60% of the diet by volume in the length range 25-29 cm. However, fish predators larger than 50 cm depended less on pelagic fish (33%), since they were also able to feed on other sources such as megafaunal invertebrates, mainly cephalopods. The pelagic fish resource was primarily exploited by 12 demersal fish species, with Merluccius merluccius and Zeus faber being the main ones feeding on small pelagics, which was related to the vertical movement of predators and prey through the water column. Survey abundance indices were used as indicators of prey abundance in the ecosystem, both for biomass and number. There was evidence for density-dependant feeding by predators on E. encrasicolus, G. argenteus and T trachurus, while the main discrepancies between abundance in the stomachs and in the surveys were due to differential availability of prey length classes in the environment. Small prey species and individuals were exploited by most demersal fish while large prey species were less accessible to predators. (C) 2007 Elsevier B.V. All rights reserved.

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Influence of seasonal variability on the trophic structure of pelagic communities

Benat Iglesias, Maite Louzao, Eneko Bachiller, Lucia Lopez-Lopez, Maria Santos, Guillermo Boyra, Eider Andonegi, Unai Cotano, Izaskun Preciado

Summary: In this study, the predator-prey interactions and trophic structure of the pelagic fish community in the Bay of Biscay were investigated using stomach content analysis and stable isotope analysis. The results showed that trophic guilds were more influenced by intra-specific affinities rather than seasonal variability. Vertically migrating meso- and macrozooplankton played an important role as a food source for the pelagic fish community, and there was high trophic overlap among most species. The trophic structure did not differ between spring and late summer, but the trophic positions were consistently lower in spring.

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