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Size-based indicators show depth-dependent change over time in the deep sea

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Mindel, BL, Neat, FC, Webb, TJ and Blanchard, JL ORCID: 0000-0003-0532-4824 2017 , 'Size-based indicators show depth-dependent change over time in the deep sea' , ICES Journal of Marine Science, vol. 75, no. 1 , pp. 113-121 , doi: 10.1093/icesjms/fsx110.

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Abstract

Size-based indicators are well established as a management tool in shelf seas as they respond to changes in fishing pressure and describe important aspects of community function. In the deep sea, however, vital rates are much slower and body size relationships vary with depth, making it less clear how size-based indicators can be applied and whether they are appropriate for detecting changes through time. The deep-sea fish stocks of the North Atlantic underwent a period of exploitation followed by management and conservation action that relieved this pressure. We used data from a deep-water bottom trawl survey in the Rockall Trough, at depths of 300–2000 m, to test whether size-based indicators changed over a 16-year period, during which fishing pressure decreased. We applied four indicators to these data: mean body length, mean maximum length, large fish indicator (LFI), and the slope of the biomass spectrum. Patterns were analysed within four different depth bands. The LFI and slope of the biomass spectrum showed positive change over time, suggesting recovery from fishing pressure. This response was generally most apparent in the shallowest depth band, where most fishing activity has been distributed. Values of the LFI were much higher overall than in shelf seas, so the same reference points cannot be applied to all marine ecosystems. These findings imply that size-based indicators can be usefully applied to the deep sea and that they potentially track changes in fishing pressure in the medium term.

Item Type: Article
Authors/Creators:Mindel, BL and Neat, FC and Webb, TJ and Blanchard, JL
Keywords: size-based indicators, deep sea, fish communities, body size, demersal fish, deep-sea fishing, size structure
Journal or Publication Title: ICES Journal of Marine Science
Publisher: Academic Press Ltd Elsevier Science Ltd
ISSN: 1054-3139
DOI / ID Number: 10.1093/icesjms/fsx110
Copyright Information:

Copyright International Council for the Exploration of the Sea 2017. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) http://creativecommons.org/licenses/by/4.0/

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