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Abundance and tidal behaviour of pelagic fish in the gateway to the Wadden Sea
Couperus, B.; Gastauer, S.; Fässler, S.M.M.; Tulp, I.; van der Veer, H.W.; Poos, J.J. (2016). Abundance and tidal behaviour of pelagic fish in the gateway to the Wadden Sea. J. Sea Res. 109: 42–51. dx.doi.org/10.1016/j.seares.2016.01.007
In: Journal of Sea Research. Elsevier/Netherlands Institute for Sea Research: Amsterdam; Den Burg. ISSN 1385-1101, more
Peer reviewed article  

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Keywords
    Clupeidae Cuvier, 1816 [WoRMS]; Marine
Author keywords
    Acoustic survey; Marsdiep; Clupeids; Tidal cycle; Sprat; North Sea

Authors  Top 
  • Couperus, B., more
  • Gastauer, S.
  • Fässler, S.M.M.
  • Tulp, I., more
  • van der Veer, H.W., more
  • Poos, J.J.

Abstract
    The shallow coast of The Netherlands is an important habitat for small pelagic fish. They form one of the major links between plankton and the higher trophic levels. Predatory fish, sea mammals and birds rely on small pelagic fish as a major food source. Currently, monitoring of fish in the Dutch coastal zone mainly focuses on demersal species, using bottom trawls and fykes. Four hydro-acoustic surveys were carried out in May and October 2010/2011 in the Marsdiep area, a relatively deep tidal inlet in the western Wadden Sea, to quantify abundances of pelagic fish. The aims of this study were to (1) describe temporal and vertical variations in fish distribution and school dimensions in relation to tide, and (2) estimate biomass of pelagic fish and their proportion to total fish biomass. The biomass of pelagic fish in the Marsdiep area ranged between 23 and 411 kg/ha. These were mainly sprat, but also young herring, anchovy and pilchard. The fish was scattered in small schools with volumes smaller than 5m3 and concentrated in the top 10 m below the surface. There was a clear effect of tidal cycle on school volume and fish abundance, with larger densities and larger schools at high tide compared to low tide. In May, sandeel contributed substantially to the pelagic assemblage, whereas in October sandeel was absent in the trawl catches, most likely because they stayed buried in the seabed from late summer to spring. The presence of pilchard and anchovy confirmed their re-establishment in the Southern North Sea and Wadden Sea. The abundance of pelagic fish exceeded the biomass of demersal fish in the western Wadden Sea by an order of magnitude. This finding is relevant for ecosystem studies. The fact that this study suggests that small pelagics outnumber demersal species to such a large extent calls for a rethinking of the allocation of monitoring effort in the Dutch coastal zone

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