Abstract
Eight whale sharks tagged with pop-up satellite archival tags off the Gulf of California, Mexico, were tracked for periods of 14–134 days. Five of these sharks were adults, with four females visually assessed to be pregnant. At least for the periods they were tracked, juveniles remained in the Gulf of California while adults moved offshore into the eastern Pacific Ocean. We propose that parturition occurs in these offshore waters. Excluding two juveniles that remained in the shallow tagging area for the duration of tracking, all sharks spent 65 ± 20.7% (SD) of their time near the surface, even over deep water, often in association with frontal zones characterized by cool-water upwelling. While these six sharks all made dives into the meso- or bathypelagic zones, with two sharks reaching the maximum depth recordable by the tags (1285.8 m), time spent at these depths represented a small proportion of the overall tracks. Most deep dives (72.7%) took place during the day, particularly during the early morning and late afternoon. Pronounced habitat differences by ontogenetic stage suggest that adult whale sharks are less likely to frequent coastal waters after the onset of maturity.
Highlights
Electronic tagging studies have revolutionised our understanding of the behaviour and spatial ecology of marine animals
This has supported the conservation of such species by provision of new information on where they range, How to cite this article Ramírez-Macías et al (2017), Oceanic adults, coastal juveniles: tracking the habitat use of whale sharks off the Pacific coast of Mexico
Our results provide some of the first insights into the detailed horizontal and vertical movements of adult whale sharks, and provide information on the spatial ecology and behaviour of this threatened species in the eastern Pacific Ocean
Summary
Electronic tagging studies have revolutionised our understanding of the behaviour and spatial ecology of marine animals Linking these movement data to key environmental processes has led to critical insights into the movements of highly migratory marine vertebrates (Pade et al, 2009; Robinson et al, 2009; Block et al, 2011). This has supported the conservation of such species by provision of new information on where they range, How to cite this article Ramírez-Macías et al (2017), Oceanic adults, coastal juveniles: tracking the habitat use of whale sharks off the Pacific coast of Mexico. Use of surface frontal zones in the open ocean represents a successful strategy to maximise prey encounter rates in patchy offshore seascapes, and has previously been documented in planktivorous sharks (Miller et al, 2015) and other pelagic shark species (Queiroz et al, 2016)
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