Journal Article

Changes in the structure and function of the North Sea fish foodweb, 1973–2000, and the impacts of fishing and climate

Michael R. Heath

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 62, issue 5, pages 847-868
Published in print January 2005 | ISSN: 1054-3139
Published online January 2005 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2005.01.023
Changes in the structure and function of the North Sea fish foodweb, 1973–2000, and the impacts of fishing and climate

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North Sea environmental and biological data were analysed to examine 30-year changes in production and consumption in the fish foodweb. The analysis revealed that the demand for secondary production placed on the ecosystem by fish declined from approximately 20 g C m−2 y−1 in the 1970s to 16 g C m−2 y−1 in the 1990s. Over the same period, the proportion of demand provided by zooplankton production increased from around 70% to 75%. The overall decrease was mainly due to a reduction in piscivorous demersal fish. Average secondary production by omnivorous zooplankton was estimated to be 35 g C m−2 y−1, and annual fluctuations were positively correlated with the gross production of planktivorous fish. The results suggest a “bottom-up” control of the pelagic foodweb. Individual planktivore species have been impacted by fishing, but the populations of other functionally similar species have expanded to fill the vacant niches, thus maintaining the planktivore role in the system. In contrast, the results indicate that benthos production was more “top-down” controlled. Overall, demersal fish species have been depleted by fishing, with no obvious species expansions to fill the vacant niche, releasing the benthos from predation pressure, and leading to an increase in benthic production and fisheries for invertebrates.

Keywords: benthos; demersal fish; fish diet; fisheries; food consumption; pelagic fish; plankton; production; stock assessment

Journal Article.  12407 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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