Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1, Canada.
Science (Impact Factor: 33.61). 03/2007; 315(5820):1846-50. DOI: 10.1126/science.1138657
Source: PubMed


Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

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    • "Most available long-term studies of fish community change were enabled by consistent long-term research surveys by government agencies (e.g. Lotze and Milewski, 2004; Myers et al., 2007; Frank et al., 2011, Ferretti et al., 2013) or standardized catch records (e.g. Britten et al., 2014). "
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    • "Many large-bodied pelagic predators are highly mobile and regularly undertake migrations of hundreds to thousands of kilometres at annual and interannual timescales (Block et al., 2011). Despite their widespread distributions, mobile pelagic predators have declined in abundance due to overfishing (Baum & Worm, 2009), causing changes to open ocean food webs (Myers et al., 2007; Worm & Tittensor, 2011). Climate-induced distribution shifts are likely to alter the functioning of pelagic ecosystems already under pressure from anthropogenic stressors (Hsieh et al., 2006; Beaugrand et al., 2008; Hazen et al., 2012; Robinson et al., 2014). "

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