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Effects of zooplankton density and diel period on surface-swimming duration of basking sharks

Published online by Cambridge University Press:  09 April 2003

D.W. Sims ,
E.J. Southall ,
D.A. Merrett  and
J. Sanders
D.W. Sims
Affiliation:
Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK
E.J. Southall
Affiliation:
Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK
D.A. Merrett
Affiliation:
Department of Biological Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK
J. Sanders
Affiliation:
Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK Institute of Marine Studies, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK
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Abstract

The surface-swimming duration of basking sharks (Cetorhinus maximus) was determined in the western English Channel from May to July over a five-year period. Surface duration showed marked variation from 0·17 to 1·45 h over the short time period from late May to mid-June. Stepwise multiple regression was used to identify any relationships between surface-swimming duration and time of day, daily sea surface temperature (SST), and zooplankton density. There was no support for any effects of SST or two measures of zooplankton density (median and maximum densities). However, there were significant relationships for surface duration with time of day and minimum zooplankton density (r2=0·50) indicating basking sharks respond to the abundance of prey and its temporal availability. This suggests that the probability of sighting sharks at the surface will vary depending on the diel period and the surface abundance of zooplankton.

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 83 , Issue 3 , June 2003 , pp. 643 - 646
Copyright
2003 Marine Biological Association of the United Kingdom

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