Commercial fishing causes dangerous fluctuations in fish populations

Current measures may not be enough to ensure sustainability - News release

Imperial College London News Release

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Wednesday 18 October 2006

Commercial fishing causes serious fluctuations in fish populations leaving them in danger of total collapse, says new research published today. These fluctuations mean current measures in place to control fish stocks may not be sufficient to ensure their sustainability.

The research, which is published in today's Nature, involved compiling the largest ever survey of both exploited fish and non-exploited fish off the California coast. The research team looked at how the abundance of both types of fish varied over a 50 year period, and found the first evidence that exploited species' population levels vary far more than non exploited species' in the same ecosystem.

Researchers concluded that this increased variability in exploited fish stocks was most likely to be caused by the effect fishing has on the age structure of a population. Heavily-fished populations are unlikely to contain any fish older than a few years old, and as such are wholly reliant on the successful growth of larvae into baby fish (recruits) to maintain population numbers year on year.

Professor John Beddington   from Imperial College London's Division of Biology, who worked on the study, explained: "Intensive fishing makes populations vulnerable because if they rely on recruits to replenish their numbers, there is always the danger that some kind of environmental factor will devastate the recruits in one season. This would leave the population close to collapse, with very few young fish coming into the group to replace those being caught."

Professor Beddington adds that the increased variability has serious implications for the way in which fish stocks are managed: "Typically fish populations are managed by governments setting total allowable catch limits (TACs), but a fixed TAC which doesn't take into account the variability of abundance over time, may mean that in some years it is completely incompatible with the population size. This means that fishing vessels could unwittingly overexploit the population, even though they are abiding by set limits."

Researchers hope that their findings will mean future decisions about fishery management take into account the variations caused by fishing, to safeguard the future of key fish populations.

-Ends-

Danielle Reeves, Imperial College London,
Tel: +44 (0)20 7594 2198
Mob: +44 (0)7803 886248
Email: Danielle.reeves@imperial.ac.uk

Notes to Editors:

1. "Fishing elevates variability in the abundance of exploited species", Nature, 19 October 2006.
Chih-hao Hsieh (1), Christian S. Reiss (2), John R. Hunter (1), John R. Beddington (3), Robert M. May (4) and George Sugihara (1).

(1) Scripps Institute of Oceanography, University of California – San Diego, 9500 Gilman Drive, La Jolla, California, 92093-0202, USA.
(2) Southwest Fisheries Science Center, National Marine Fisheries Service, 8604 La Jolla Shoers Drive, La Jolla, California, 92037-1508, USA.
(3) Division of Biology, Faculty of Natural Sciences, Imperial College London, RSM Building, South Kensington Campus, London, SW7 2AZ, UK.
(4) Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS.

2. Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (11,000) and staff (6,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture. Website: www.imperial.ac.uk