Global efforts over the past decade to conserve this species have aimed to better understand its movement ecology (Andrzejaczek et al., 2016 McKinney et al., 2017) however, knowledge gaps still remain in understanding the movement patterns of whale sharks after departing their seasonal aggregations. Recent population declines have resulted in the upgrading of whale sharks to globally Endangered on the IUCN Red List of Threatened Species in 2016 (Pierce & Norman, 2016). Despite the successes of these ecotourism ventures (Zimmerhackel et al., 2019), anthropogenic impacts, such as targeted fisheries catches, bycatch in nets, and vessel strikes, continue to jeopardize global whale shark populations (Pierce & Norman, 2016) and, as a consequence, the persistence of this tourism industry.
The reliable aggregation of whale sharks at coastal localities has facilitated the development of an increasingly valuable tourism industry in the past three decades, where divers and snorkelers are able to swim with and observe individuals (Anderson et al., 2014 Gallagher & Hammerschlag, 2011 Zimmerhackel et al., 2019). In addition to undertaking large‐scale movements (e.g., >7,000 km Hueter et al., 2013) and crossing international boundaries, these filter‐feeding sharks aggregate seasonally at numerous locations around the world (Sequeira et al., 2013). TL 20 m) elasmobranchs that live in warm temperate‐tropical waters (Rowat & Brooks, 2012). Whale sharks ( Rhincodon typus) are large (max. A crucial first step in identifying the threats faced by marine megafauna and in mitigating their potential impacts on populations is to describe the distribution and movement patterns of these vulnerable species (Hammerschlag et al., 2011 Hays et al., 2016). In addition, such movements complicate conservation and management efforts through the need for coordinated efforts among many nations and international organizations (Lascelles et al., 2014). These international movements may expose migrating animals to a number of anthropogenic threats, including fluctuating levels of fishing pressure and shipping activity, that together with the varying extent of legal protection encountered through movements and the conservative life histories of many megafauna species, can have large‐scale impacts on populations (Hays et al., 2019). Marine megafauna are typically highly mobile species with migration pathways that can cross the boundaries of multiple national jurisdictions (Block et al., 2011 Sequeira et al., 2018). Area‐based management approaches focusing on seasonal hotspots offer a way forward in the conservation of whale sharks in the Western Indian Ocean. In addition, wide‐ranging movements through multiple nations, as well as the high use of surface waters recorded, likely exposes whale sharks in this region to several anthropogenic threats, including targeted and bycatch fisheries and ship‐strikes. Long‐distance movements recorded both here and in previous studies suggest that connectivity between the whale sharks tagged at the Djibouti aggregation and other documented aggregations in the region are likely within annual timeframes. Vertical movement data revealed high occupation of the top ten meters of the water column, diel vertical movement patterns, and deep diving behavior. Tags revealed movements ranging from local‐scale around the Djibouti aggregation site, regional movements along the coastline of Somaliland, movements north into the Red Sea, and a large‐scale (>1,000 km) movement to the east coast of Somalia, outside of the Gulf of Aden. To gain insight into whale shark ( Rhincodon typus) movement patterns in the Western Indian Ocean, we deployed eight pop‐up satellite tags at an aggregation site in the Arta Bay region of the Gulf of Tadjoura, Djibouti in the winter months of 2012, 2016, and 2017.
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