The Influence of Biotic and Abiotic Factors on the Spatiotemporal Distribution of the Basking Shark (Cetorhinus maximus)

• Main Author: Sanders, Jeanette Louise
• Format: Thesis
• Language: English
• Published: 2002
• Subjects: Cetorhinus maximus; North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/10026.2/2094

This study investigated the theory that basking sharks forage along frontal systems in order to locate the most productive areas of zooplankton occurrence. The association of basking sharks with different bodies of water was investigated, as was their spatial distribution throughout the study area and period. The results indicate that a significant association of basking sharks with frontal water is evident, at both large and small-scale, and that the appearance of basking sharks within the study area is not due to stochastic processes. The study also investigated the relationship between zooplankton density and basking shark locations. The results concurred with previous studies, to show that basking sharks selectively feed in areas of greatest zooplankton density. Within these areas, the calanoid copepod Calanus helgolandicus contributed most to overall biomass. The length of time sharks were observed upon the surface in this study was directly related to the density of zooplankton, which has important implications for calculating the likelihood of locating basking sharks. The North Atlantic Oscillation was shown to correlate with zooplankton density at two temporal scales, firstly with a phase lag of one month and secondly with a phase lag of two years. The mechanism for this relationship has not been identified but the study demonstrated that variations in wind strength and direction correlated with changes in zooplankton density. No evidence was found for a direct link between either the NAO, or wind patterns and the distribution of basking sharks. The study concluded that, in general, basking shark distribution, during spring, reflects changes in the location of the principal frontal systems in the English Channel. Any effect of weather or climate factors on their distribution would be indirect, acting via processes such as seasonal stratification and sporadic breakdown of thermoclines. Dr David Sims and the Fish Biology Research Group MBA, Plymouth