Abstract
Animal migration is ubiquitous in nature with individuals within a population often exhibiting varying movement strategies. The basking shark (Cetorhinus maximus) is the world’s second largest fish species, however, a comprehensive understanding of their long-term wider-ranging movements in the north-east Atlantic is currently lacking. Seventy satellite tags were deployed on basking sharks over four years (2012–2015) off the west coast of Scotland and the Isle of Man. Data from 28 satellite tags with attachment durations of over 165 days reveal post-summer ranging behaviours. Tagged sharks moved a median minimum straight-line distance of 3,633 km; achieving median displacement of 1,057 km from tagging locations. Tagged individuals exhibited one of three migration behaviours: remaining in waters of UK, Ireland and the Faroe Islands; migrating south to the Bay of Biscay or moving further south to waters off the Iberian Peninsula, and North Africa. Sharks used both continental shelf areas and oceanic habitats, primarily in the upper 50–200 m of the water column, spanning nine geo-political zones and the High Seas, demonstrating the need for multi-national cooperation in the management of this species across its range.
Highlights
Animal migration is ubiquitous in nature with individuals within a population often exhibiting varying movement strategies
The ability to record intra- and inter-individual variation in the movement and distribution of large marine vertebrates is becoming increasingly possible and provides important information on species space-use[3,4,5,31], and has resulted in migration being observed in many taxa[1,28]
Our study provides the most detailed investigation of basking shark ranging behaviours in the north-east Atlantic over seasonal timescales to be informed by satellite tracking[32]
Summary
Animal migration is ubiquitous in nature with individuals within a population often exhibiting varying movement strategies. Tagged individuals exhibited one of three migration behaviours: remaining in waters of UK, Ireland and the Faroe Islands; migrating south to the Bay of Biscay or moving further south to waters off the Iberian Peninsula, and North Africa Sharks used both continental shelf areas and oceanic habitats, primarily in the upper 50–200 m of the water column, spanning nine geo-political zones and the High Seas, demonstrating the need for multi-national cooperation in the management of this species across its range. Studies in the region have successfully tracked basking sharks for up to 245 days, showing movements into the open ocean, the waters of the Bay of Biscay[19,20] and one trans-Atlantic crossing[14] These studies have been limited by sample size, with the majority of movements confined to the continental shelf of the north-east Atlantic (n = 214, n = 719,21,22, n = 920). Basking sharks are considered to be vulnerable to interactions with commercial fishing; potentially becoming entangled in set nets, pot lines or caught incidentally in trawls, and is considered as one of the more valued fins within the shark fin trade[13]
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