Ransom_etal__Top_Predator_Declin

Ransom_etal__Top_Predator_Declin - letters to nature Rapid...

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.............................................................. Rapid worldwide depletion of predatory Fsh communities Ransom A. Myers & Boris Worm Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1 ............................................................................................................................................................................. Serious concerns have been raised about the ecological effects of industrialized Fshing 1–3 , spurring a United Nations resolution on restoring Fsheries and marine ecosystems to healthy levels 4 . However, a prerequisite for restoration is a general understand- ing of the composition and abundance of unexploited Fsh communities, relative to contemporary ones. We constructed trajectories of community biomass and composition of large predatory Fshes in four continental shelf and nine oceanic systems, using all available data from the beginning of exploita- tion. Industrialized Fsheries typically reduced community bio- mass by 80% within 15 years of exploitation. Compensatory increases in fast-growing species were observed, but often reversed within a decade. Using a meta-analytic approach, we estimate that large predatory Fsh biomass today is only about 10% of pre-industrial levels. We conclude that declines of large predators in coastal regions 5 have extended throughout the global ocean, with potentially serious consequences for eco- systems 5–7 . Our analysis suggests that management based on recent data alone may be misleading, and provides minimum estimates for unexploited communities, which could serve as the ‘missing baseline’ 8 needed for future restoration efforts. Ecological communities on continental shelves and in the open ocean contribute almost half of the planet’s primary production 9 , and sustain three-quarters of global Fshery yields 1 . The widespread decline and collapse of major Fsh stocks has sparked concerns about the effects of overFshing on these communities. Historical data from coastal ecosystems suggest that losses of large predatory Fshes, as well as mammals and reptiles, were especially pronounced, and precipitated marked changes in coastal ecosystem structure and function 5 . Such baseline information is scarce for shelf and oceanic ecosystems. Although there is an understanding of the magnitude of the decline in single stocks 10 , it is an open question how entire communities have responded to large-scale exploitation. In this paper, we examine the trajectories of entire communities, and estimate global rates of decline for large predatory Fshes in shelf and oceanic ecosystems. We attempted to compile all data from which relative biomass at the beginning of industrialized exploitation could be reliably estimated. ±or shelf ecosystems, we used standardized research trawl surveys in the northwest Atlantic Ocean, the Gulf of Thailand and the Antarctic Ocean off South Georgia, which were designed to estimate the biomass of large demersal Fsh such as codFshes (Gadidae), flatFshes (Pleuronectidae), skates and rays (Rajiidae), among others (see Supplementary Information for detailed species information). In all other shelf areas for which we could obtain data,
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Ransom_etal__Top_Predator_Declin - letters to nature Rapid...

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