Biodiversity loss in the ocean: how bad is it?

THE RESEARCH ARTICLE "IMPACTS OF BIODIVERSITY LOSS ON OCEAN ECOSYSTEM SERVICES" BY B. Worm et al. (3 Nov. 2006, p. 787) projects that 100% of seafood-producing species stocks will collapse by 2048. The projection is inaccurate and overly pessimistic. Worm et al. define "collapse" as occurring when the current year's catch is <10% of the highest observed in a stock's time series. However, fish catch is rarely an adequate proxy for fish abundance, particularly for rebuilding stocks under management. A variety of biological, economic, and social factors and management decisions determine catches; low catches may occur even when stocks are high (e.g., due to low fish prices or the effects of restrictive management practices), and vice versa. The inadequacy of Worm et al. 's abundance proxy is illustrated by the time series of data for Georges Bank haddock {Melanogrammus aeglefinus). The highest catch for haddock occurred in 1965 at 150,362 tons (7). This catch occurred during a period of intense domestic and international fishing (7). In 2003, haddock catch was 12,576 tons, or 8% of the time series maximum. Under the Worm et al. definition, the stock would be categorized as collapsed in 2003. However, stock assessment data (7) estimate the total magnitude of the spawning biomass in 2003 to be 91% of that in 1965. Comparing the estimate of spawning stock biomass in 2003 to the level producing maximum sustainable yield (MSY), the stock was not even being overfished in 2003 (2). Because adequate stock abundance measures exist for only a portion of world fish stocks, this purported worldwide meta analysis required using data that represent the lowest common denominator of data—the total magnitude of the catch. However, if the catch ratio metric is so prone to misrepresentation of the true status of populations, as illustrated above, a synthesis of world fisheries based on these data is equally flawed. At the least, the authors should have conducted a calibration of their stock collapse metric with more complete stock abundance data available from the many worldwide sources where such data exist. The extrapolation of their stock collapse metric to 100% by 2048 does not agree with the recent history of stock status, particularly in the United States. National Marine Fisheries Service data indicate that for 2005, about 26% of stocks were classified as "overfished" (2). For most stocks, overfished status occurs when the population size drops below 50% of the population required to support MSY. Even under this more conservative definition of stock reduction, the proportion of stocks classified as overfished is actually declining slightly; in 2004, 28% of stocks were so classified. Extrapolating a 2% decrease in the number of overfished stocks per year leads to a prediction that no stocks in U.S. jurisdiction would be overfished by the year 2018. However, such a meaningless projection does not incorporate a large number of complex factors, such as the differing life histories of species, impacts of variable ocean conditions on recruitment, and the increasing effectiveness of management measures, all significant shortcomings of the prediction method and data of Worm et al. To address persistent overfishing issues, in December 2006 the U.S. Congress passed and the National Marine Fisheries Service is now implementing provisions of the Magnuson Stevens Fishery Conservation and Management Act Reauthorization Act (MSRA). The law mandates that overfishing be eliminated for all federally managed species by 2010 and that science-based annual catch limits will be calculated for all of the 532 stocks currently under regulation. STEVEN MURAWSKI, RICHARD METHOT, GALEN TROMBLE