Basking shark breaching behaviour observations west of Shetland

Emma Hayes,Matthew J Witt,Brendan J Godley,Maja Nimak-Wood

doi:10.1186/s41200-018-0151-4

Emma Hayes, Matthew J Witt + Show 2 more

Open Access

https://doi.org/10.1186/s41200-018-0151-4

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Abstract

This study reports observations of basking sharks (Cetorhinus maximus) sighted during an offshore geophysical survey conducted in July and August 2013, west of Shetland, UK. During the 38-day survey, trained and dedicated marine wildlife observers recorded 19 sightings of basking sharks (n = 22 individuals). Of these observations, 17 were of single sharks, with one observation of two sharks and one observation of three sharks. All surface sightings occurred in water depths between 129 and 199 m, predominantly prior to noon local time (79%), and were mostly of sharks 6–8 m in length, although a young (2 m) individual was also recorded. Breaching behaviour was observed on 21 occasions, by individuals or in small groups. Breaching has been proposed as a male-male competitive behaviour during courtship displays and female basking sharks may breach to signal their readiness for mating. Aggregations of basking sharks at frontal systems are well documented and linked to the occurrence of prey patches; however, these oceanographic features may also be of importance to courtship. The high number of sightings of sharks recorded during a relatively short time frame in addition to breaching behaviour and presence of young individuals, suggest that this area west of Shetland may be an important habitat for the basking shark.

Highlights

The basking shark (Cetorhinus maximus) is the largest fish in UK waters and the second largest fish globally, reaching 12 m in length and weighing up to 4 t (Sims, 2008)
This study reports upon the sighting of basking sharks breaching to the west of Shetland, observed during marine wildlife observations made during 2D seismic survey activity
Basking sharks were observed breaching clear of the water on 21 occasions (Fig. 2a)

Summary

Introduction

The basking shark (Cetorhinus maximus) is the largest fish in UK waters and the second largest fish globally, reaching 12 m in length and weighing up to 4 t (Sims, 2008). Basking sharks have been shown to feed where water masses meet, such as at interfaces between bodies of water, including tidal and oceanic fronts, typically with strong thermal gradients (Sims, 2008; Priede & Miller, 2009). At these fronts, plankton are typically found in higher concentrations (Sims & Quayle, 1998). Sightings in the Northeast Atlantic are usually recorded between April and October, with the peak number of sightings between June and August (Witt et al, 2012).

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