Fish abundance with no fishing: predictions based on macroecological theory
Article first published online: 16 JUN 2004
Journal of Animal Ecology
Volume 73, Issue 4, pages 632–642, July 2004
How to Cite
Jennings, S. and Blanchard, J. L. (2004), Fish abundance with no fishing: predictions based on macroecological theory. Journal of Animal Ecology, 73: 632–642. doi: 10.1111/j.0021-8790.2004.00839.x
- Issue published online: 16 JUN 2004
- Article first published online: 16 JUN 2004
- Received 11 November 2003; accepted 28 November 2003
- abundance–body mass relationships;
- energetic equivalence;
- fishing effects;
- metabolic scaling theory;
- predator–prey relationships;
- size spectra
- 1Fishing changes the structure of fish communities and the relative impacts of fishing are assessed usefully against a baseline. A comparable baseline in all regions is fish community structure in the absence of fishing.
- 2The structure of unexploited communities cannot always be predicted from historical data because fisheries exploitation usually precedes scientific investigation and non-fisheries impacts, such as climate change, modify ecosystems over time.
- 3We propose a method, based on macroecological theory, to predict the abundance and size-structure of an unexploited fish community from a theoretical abundance–body mass relationship (size spectrum).
- 4We apply the method in the intensively fished North Sea and compare the predicted structure of the unexploited fish community with contemporary community data.
- 5We suggest that the current biomass of large fishes weighing 4–16 kg and 16–66 kg, respectively, is 97·4% and 99·2% lower than in the absence of fisheries exploitation. The results suggest that depletion of large fishes due to fisheries exploitation exceeds that described in many short-term studies.
- 6Biomass of the contemporary North Sea fish community (defined as all fishes with body mass 64 g−66 kg) is 38% lower than predicted in the absence of exploitation, while the mean turnover time is almost twice as fast (falls from 3·5 to 1·9 years) and 70% less primary production is required to sustain it.
- 7The increased turnover time of the fish community will lead to greater interannual instability in biomass and production, complicating management action and increasing the sensitivity of populations to environmental change.
- 8This size-based method based on macroecological theory may provide a powerful new tool for setting ecosystem indicator reference levels, comparing fishing impacts in different ecosystems and for assessing the relative impacts of fishing and climate change.