Comment on “As tuna vanish, sardines rise”. News coverage of an oral presentation at the annual American Association for the Advancement of Science, by Villy Christensen from the UBC Fisheries Centre provided the most optimistic appraisal of the status of world fisheries yet.
The coverage says that Christensen argued that “The biomass of large fish has declined by two-thirds over the last 100 years” and “the fish that were once preyed on by these large fish have increased. The rise in their biomass is just 0.85% per year, but that has led to more than a doubling over the past century.”
Why is this so optimistic?
Just 8 years ago world headlines splashed the news that the large fish of the ocean had declined 90% in just 30 years (from 1950 to 1980), now we are told that they have only declined by 2/3 over 100 years. Not only is the decline less, but the 2/3 decline is exactly what is supposed to happen in a well managed fishery in order to produce maximum sustained yield.
Thus Christensen is telling us that, on average, the large fish of the ocean are now at a level that produces maximum sustained yield … they are not overfished, they are not collapsed, they are at exactly the level that national and international law says they should be!
This is a slightly more optimistic interpretation than provided in the 2009 paper that Boris Worm, I and 19 co-authors published showing based on abundance data, that most fish stocks were now harvested at rates that would produce MSY, but that most remained below target levels of abundance.
So if you combine Christensen's assessment that the large fish are at 33% of their original abundance, and the Worm et al. data showing they are now mostly fished at sustainable levels, you have some very good news.
But there is even better news. While the large fish have been fished to the level that produces maximum sustainable yield, Christensen's models project that the smaller fish of the world have doubled in abundance. We have been repeatedly told that these fish, also known as forage fish, are in deep trouble.
Christensen's colleague Daniel Pauly has said for years that the forage fish are also in decline and soon there will be nothing to eat but jellyfish. According to Christensen this isn't so, and the forage fish are actually increasing.
This increase is apparently is despite the fact that the catches of for forage fish have been very high for 60 years, and we have seen the decline, collapse, and rebuilding of many of these major stocks, including Peruvian anchoveta, California sardine, several European herring stocks, Japanese sardine, Northwest Atlantic Herring etc.
So despite the best efforts of world fishing fleets, these forage fish that provide perhaps 25% of the worlds catch, have doubled in abundance. Wow!
That is certainly good news!
But a note of caution. If as the news reports suggest all of Christensen's analysis is based on models, one has to be very skeptical. The data assembled by the team that produced the Worm et al. 2009 paper, which are actual trends in abundance and fishing pressure, suggest that the forage fish are in fact fully exploited, and there isn't a lot of room for increased yields. Even if the large fish are, on average, at the right level, we know some stocks are overfished and collapsed. Let us make sure we don't lose sight of those stocks, who need major reductions in fishing pressure, amid the euphoria caused by Christensen's analysis.
(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.)
This column is re-published with permission from Seafood News, Feb. 22, 2011