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Reconsidering the consequences of selective fisheries

Posted on 5 March 2012

A new study by an international team of researchers is calling for a rethink on the most appropriate way to reduce commercial fishing’s impacts on ecosystems and fisheries productivity.

A “Policy Forum” analysis by the team, which included Professor Richard Law, of the Department of Biology at the University of York, suggests that the approach of increasing selectivity in the size and species of fish that can be harvested should be reconsidered.

There are potentially real benefits to be gained by moving towards more balanced exploitation of marine ecosystems

Professor Richard Law

In the analysis, published in Science, the  researchers argue that utilizing a ‘balanced harvest’ approach to fishing – in which moderate levels of mortalities are distributed proportionately to the species productivity over the widest possible range of species, stocks and sizes in an ecosystem – could mitigate adverse effects and address food security better than increased selectivity.

Professor Law, who is also a member of YCCSA – the York Centre for Complex Systems Analysis – says:  “Heavy selective fishing has caused structural changes to fish communities in the North Sea and elsewhere. In contrast, in several African small-scale inland fisheries, the fish size spectrum – a measure of community structure – has been maintained under intensive and diverse fishing activities that cause high mortality with low selectivity.”

In theory, increased selectivity helps prevents growth overfishing – the loss of future yields if juveniles are caught before they are allowed to reproduce – and reduces by-catch of non-targeted species.  But by synthesizing data across ecosystem models from 30 fisheries worldwide, the researchers found that these benefits occur only at levels of fishing mortalities so low that yield in the fishery is not economically sustainable. 

In contrast, they found compelling evidence that when fishing is spread over more functional groups and sizes, yields are higher and harmful impacts, such biomass depletions and extinctions of local populations, are lower across a broad percentage of system removals (roughly, total catch as a proportion of total biomass).

In their analysis, the researchers propose that ecosystem modeling could help to determine appropriate patterns of fishing mortality and selectivity, allowing managers to set sustainable limits for catch sizes and total removals – including discards, not just landings. In a system where each component of the ecosystem is utilized in appropriate amounts, by-catch of non-targeted fish species would become part of the management strategy. Market incentives could be developed to promote the increased use of these traditionally less-utilized species as animal feed or for human consumption.

Professor Law adds: "Working with Dr Michael Planck, of the University of Canterbury, New Zealand and Dr Jeppe Kolding, of the University of Bergen, Norway, I have checked the sums underlying this argument in a separate article just published in the ICES Journal of Marine Science. These simulations also show there are potentially real benefits to be gained by moving towards more balanced exploitation of marine ecosystems."

The analysis published in Science also involved researchers from the International Union for Conservation of Nature Commission on Ecosystem Management’s Fisheries Expert Group (Belgium); the IUCN Global Marine Program (Switzerland); the University of Bergen (Norway); the Department of Fisheries and Oceans (Canada); L’Institut Francais de Recherche pour l’Exploitation de la Mer (France); CSIRO Marine and Atmospheric Research (Australia); Tokyo University of Marine Sciences and Technology (Japan); the Danish National Institute of Aquatic Resources; FishFix, Brussels, Belgium; the Bedford Institute of Oceanography (Canada); the Inter-American Tropical Tuna Commission (United States); Nicholas School of the Environment, Duke University (United States);  International Institute for Applies systems Analysis (Austria); the Institute of Marine Research (Norway); the Fisheries Research Agency (Japan); and the Institute for Marine Resources and Ecosystems Studies (the Netherlands).

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