Environmental drivers of variation in shellfish landings in Shetland creel fisheries

Catch rates of crustaceans in creel fisheries are closely linked to a range of environmental factors. Environmental effects on landings of brown crab (<i>Cancer pagurus</i>), velvet crab (<i>Necora puber</i>) and European lobster (<i>Homarus gammarus</i>) from creel fisheries in Shetland were investigated using data from a fishers’ logbook programme. The study aimed to identify relationships between the spatiotemporal landings per unit effort (LPUE) of each species and variables including sea surface temperature (SST), chlorophyll <i>a</i> concentrations (Chl <i>a</i>), wind speed and direction and tidal current speed. Exploratory time series analyses in four areas using generalised additive mixed models (GAMMs) revealed that differenced SST and Chl <i>a</i> (with seasonal trends removed) had very little effect on LPUE of any species. Wind speed also had little effect and wind direction had very subtle effects which were not spatially consistent for each species. LPUE increased with tidal current speed in one area, before declining at higher speeds. LPUE followed similar seasonal trends for each species, with the highest landings generally occurring in late summer and early autumn for brown crab and lobster, and in late autumn and early winter for velvet crab. It was suggested that seasonal cycles in LPUE are linked not only to absolute temperatures, but to biological processes that also follow seasonal cycles, such as moulting and reproduction. Further investigation into spatiotemporal differences in catch composition, such as sex and size ratios, would improve interpretation of results and help devise management strategies in relation to seasonal biological processes of each species.

Name dc:type.qualificationname

Master of Science (awarded by UHI)

Level dc:type.qualificationlevel

Master's Thesis

Grantor dc:publisher.institution

University of Aberdeen

Year dc:date.issued

2016

Author dc:creator

• Hamilton, Mark

Advisors dc:contributor.advisor

• Scott, Beth E.
• Mouat, Beth
• Tweddle, Jacqueline F.

Language dc:language

eng

Identifier

oai:pure.atira.dk:studenttheses/e2a8b5b4-3055-45ca-97b0-3cbab2984943

OAI record oai:identifier

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