Assessing the importance of Isle of Man waters for the basking shark Cetorhinus maximus

Hr Dolton,J Hall,La Hawkes,G Hall,Mj Witt,Fr Gell

doi:10.3354/esr01018

Hr Dolton, J Hall + Show 4 more

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https://doi.org/10.3354/esr01018

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Abstract

Satellite tracking of endangered or threatened animals can facilitate informed conservation by revealing priority areas for their protection. Basking sharks Cetorhinus maximus (n = 11) were tagged during the summers of 2013, 2015, 2016 and 2017 in the Isle of Man (IoM; median tracking duration 378 d, range: 89-804 d; median minimum straight-line distance travelled 541 km, range: 170-10406 km). Tracking revealed 3 movement patterns: (1) coastal movements within IoM and Irish waters, (2) summer northward movements to Scotland and (3) international movements to Morocco and Norway. One tagged shark was bycaught and released alive in the Celtic Sea. Basking sharks displayed inter-annual site fidelity to the Irish Sea (n = 3), a Marine Nature Reserve (MNR) in IoM waters (n = 1), and Moroccan waters (n = 1). Core distribution areas (50% kernel density estimation) of 5 satellite tracked sharks in IoM waters were compared with 3902 public sightings between 2005 and 2017, highlighting west and south coast hotspots. Location data gathered from satellite tagging broadly correspond to the current boundaries of MNRs in IoM waters. However, minor modifications of some MNR boundaries would incorporate ~20% more satellite tracking location data from this study, and protective measures for basking sharks in IoM waters could further aid conservation of the species at local, regional and international scales. We also show the first documented movement of a basking shark from the British Isles to Norway, and the longest ever track for a tagged basking shark (2 yr and 2 mo, 804 d).

Highlights

Many animal taxa, including birds, fish and mammals, seasonally migrate to make use of natural fluctuations in available resources that are needed to support growth and reproduction, and to avoid harsh environmental conditions and predators (Hawkes et al 2011, Hopcraft et al 2014, Hammerschlag et al 2015, Leroy et al 2016, Peiman et al 2017)
Satellite tags were deployed on basking sharks using a titanium M-style dart (Wildlife Computers), attached by a stainless steel flexible cable covered in heat-shrink tubing, a swivel and monofilament line, which attached to the tag
Basking sharks tagged in Isle of Man (IoM) waters exhibit a variety of movement patterns, with some remaining for extended periods in IoM waters and the Irish Sea during the summer, while others move to the Sea of Hebrides in Scotland, and more (2 in the present study) making long-distance movements crossing international boundaries, travelling approximately 10 000 km and 6000 km to waters off Morocco and Norway, respectively

Summary

Introduction

Many animal taxa, including birds, fish and mammals, seasonally migrate to make use of natural fluctuations in available resources that are needed to support growth and reproduction, and to avoid harsh environmental conditions and predators (Hawkes et al 2011, Hopcraft et al 2014, Hammerschlag et al 2015, Leroy et al 2016, Peiman et al 2017). Marine protected areas (MPAs) have been demonstrated to benefit many different marine species and habitats (Angulo-Valdés & Hatcher 2010), but are less effective with highly mobile species (Hooker & Gerber 2004) and so can only offer protection from anthropogenic threats if they use the best available evidence (Runge et al 2014). Technologies such as satellite tracking can aid informed design and management of MPAs, as successful designation relies on good biological knowledge of the core activity areas, or hotspots, of a species (Doherty et al 2017b). Basking sharks are listed as ‘Endangered’ globally by the International Union for Conservation of Nature (IUCN) (Rigby et al 2019)

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