SEAFOOD.COM NEWS by Ray Hilborn – Dec 6, 2010
Prof. Ray Hilborn, of the University of Washington, is one of the leading global researchers on adaptive ecosystem management for fisheries. He has consistently argued that the doomsday narrative of continuous global overfishing is not supported by facts; that instead where good fisheries management is applied, fisheries and ecosystems are stable, thriving, and producing huge economic benefits. Given the prominence of the controversies over seafood sustainability, Ray and some of his colleagues have agreed to write a series of occasional comments for Seafoodnews.com when major fisheries papers or ideas about sustainability are published or discussed.
Today's comment regards the paper published last week by Swartz et al. New Pauly study says that expansion of fishing fleets overwhelming new geographical areas to fish.
A recent paper by Swartz et al. argues that the area around the world being fished expanded in the 1980s and 1990s so that most of the worlds continental shelves are now being fished. The authors then suggest that this means that there are no new places for fisheries expansion. Essentially we have found all the major fish stocks of the world and we are exploiting them.
This result is not new and I believe it is widely accepted. In a paper published this summer by Sethi and others in Proceedings of the National Academy of Sciences, the authors showed that all of the major fish species of the world were being exploited by 1990 Ð while new fish stocks have been added since then, these new species are insignificant in terms of world catch and seafood security.
Essentially the spatial expansion since 1990 has been largely irrelevant to world fish production. Fishing fleets had found all the fish by 1990. Swartz and authors then argue that this expansion means that most fisheries are not currently sustainable and harvest must be reduced to achieve sustainability. However, we know much more about the current sustainability of fishing pressure.
In a paper in Science in 2009 Worm et al. looked at the rate of exploitation rate for individual stocks around the world, a much better measure of the sustainability of exploitation. Their data show that only 17% of the world fish stocks for which they had data are now fished so hard the stocks would be considered overfished by U.S. standards if the current fishing pressure is maintained. It is those 17% of fish stocks, including bluefin tuna and many sharks for instance, that are in urgent need of reduced fishing pressure.
However for all the other 83% of fish stocks, current fishing pressure is sustainable and would produce near maximum long term food production if we continue as we are now. Thus we can assure world seafood security by reducing pressure in only 17% of fish stocks. If we want to achieve current biomass targets then the data in Worm et al. suggest that another 17% or so of stocks need further fishing reductions. Reduction of fishing pressure in these stocks will not significantly decrease food production, but will reduce ecosystem impacts of fishing and the economic profitability of fisheries.
Swartz et al. use the ratio between primary production and fisheries catch as an index of overfishing. They present a figure showing much of the world as red an indication of exploitation rates they argue are not sustainable.
Yet those red areas include the best managed areas in the world where we know from detailed data that fishing is very sustainable. These areas include the eastern Bering sea, the west coast of the United States, New Zealand and the Barents Sea. This is simply another effort to use catch data to indicate the status of marine fisheries and we have lots of evidence using catch data does not work. The all fish will be gone by 2048 was based on analysis of catch trends. When we looked at abundance trends in Worm et al. 2009 we found no indication of overall declines in stock biomass.
This paper paints a picture of global concern about the sustainability of fisheries rather than more specifically targeting the fisheries where problems in seafood security are pressing.
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