Sized-based indicators show depth-dependent change over time in the deep sea
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ICES Journal of Marine Science
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Size-based indicators are well established as a management tool in coastal seas as they respond to changes in fishing pressure and describe important aspects of community function. However, they have not yet been applied to the deep sea with the same rigour, despite the increasing exploitation pressure on this ecosystem. We use data from a deep-water bottom trawl survey in the Northeast Atlantic, at depths of 300-2000 m, to test whether size-based indicators show recovery from exploitation over a 16-year period during which fishing pressure had decreased. We apply five indicators to these data: mean body length, mean maximum length, Large Fish Indicator (LFI), slope of biomass spectrum, and fractional size. Patterns were analysed within four different depth bands. The LFI, slope of biomass spectrum and fractional size showed positive change over time, suggesting recovery from fishing pressure. This response was generally most apparent in the shallowest depth band, when most fishing activity has been distributed. Values of LFI were much higher overall than in coastal seas, so the same reference points cannot be applied to all marine ecosystems. These findings imply that size-based indicators can be applied to the dep sea with the same efficacy as in coastal waters and that deep-sea fish assemblages are able to recover from fishing pressure int he medium-term.
Mindel, B. L., Neat, F. C., Webb, T. J. & Blanchard, J. L. (2018). Sized-based indicators show depth-dependent change over time in the deep sea. ICES Journal of Marine Science, 75(1), 113-121
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