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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on July 8, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(10):2211-2218; doi:10.1093/icesjms/fsp190
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Fuzzy diel patterns in catchability of deep-water species on the continental margin

Nixon Bahamon1, Francesc Sardà2 and Jacopo Aguzzi2

1 Centre d'Estudis Avançats de Blanes (CSIC), Carrer accés Cala St Francesc 14, 17300 Blanes, Spain
2 Institut de Ciències del Mar (CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain

Correspondence to N. Bahamon: tel: +34 972 336101; fax: +34 972 337806; e-mail: bahamon{at}ceab.csic.es

Bahamon, N., Sardà, F., and Aguzzi, J. 2009. Fuzzy diel patterns in catchability of deep-water species on the continental margin. – ICES Journal of Marine Science, 66: 2211–2218.

Exploited deep-water fish communities on continental margins are poorly understood in terms of variations in species composition and abundance by depth and season as a response to diel changes in light intensity and length of photoperiod. Innovative fuzzy clustering and traditional agglomerative hierarchical clustering methods were applied to data from bottom trawls collected continuously for 4 d in October and June, on the shelf (100–110 m) and upper slope (400–430 m). Fuzzy clustering was more effective than hierarchical clustering at characterizing diel variations in catches from the upper slope because the species assemblage did not show a distinct day and night structure. On the shelf, the species assemblages shifted abruptly between a diurnal and a nocturnal structure at sunset and sunrise, and the two clustering methods yielded similar results. Endobenthic decapods with marked crepuscular-nocturnal emergence from the substratum were mostly responsible for this pattern. No clearly discernible diel pattern was found with the dampening of light intensity with depth, weakening the behavioural response of endobenthos to the day–night cycle. The results indicated that the regulatory effect of the light cycle on diel activity rhythms weakens with depth.

Keywords: bottom trawl catches, catch assessment surveys, fuzzy clustering, hierarchical clustering, Mediterranean Sea, multispecies fishery

Received 17 December 2008; accepted 3 June 2009; advance access publication 8 July 2009.


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