Abstract
The Arabian Gulf is the warmest sea in the world and is host to a globally significant population of the whale shark Rhincodon typus. To investigate regional whale shark behaviour and movements, 59 satellite-linked tags were deployed on whale sharks in the Al Shaheen area off Qatar from 2011–14. Four different models of tag were used throughout the study, each model able to collect differing data or quantities of data. Retention varied from one to 227 days. While all tagged sharks crossed international maritime boundaries, they typically stayed within the Arabian Gulf. Only nine sharks dispersed through the narrow Strait of Hormuz into the Gulf of Oman. Most sharks stayed close to known or suspected feeding aggregation sites over summer months, but dispersed throughout the Arabian Gulf in winter. Sharks rarely ventured into shallow areas (<40 m depth). A single, presumably pregnant female shark was the sole animal to disperse a long distance, crossing five international maritime boundaries in 37 days before the tag detached at a distance of approximately 2644 km from the tagging site, close to the Yemeni-Somali border. No clear space-use differentiation was evident between years, for sharks of different sizes, or between sexes. Whale sharks spent the most time (~66%) in temperatures of 24–30°C and in shallow waters <100 m depth (~60%). Sharks spent relatively more time in cooler (X2 = 121.692; p<0.05) and deeper (X2 = 46.402; p<0.05) water at night. Sharks rarely made dives deeper than 100 m, reflecting the bathymetric constraints of the Gulf environment. Kernel density analysis demonstrated that the tagging site at Al Shaheen was the regional hotspot for these sharks, and revealed a probable secondary aggregation site for whale sharks in nearby Saudi Arabian waters. Analysis of visual re-sightings data of tagged sharks revealed that 58% of tagged individuals were re-sighted back in Al Shaheen over the course of this study, with 40% recorded back at Al Shaheen in the year following their initial identification. Two sharks were confirmed to return to Al Shaheen in each of the five years of study.
Highlights
The world’s largest fish, the whale shark, Rhincodon typus (Smith, 1828), has routinely been described as enigmatic [1,2], as aspects of its biology and habitat use remain poorly understood
Due to the whale sharks endangered status [24], known bycatch in surrounding areas [24], and susceptibility to injury from large vessel traffic [25], we aimed to investigate the movement ecology of the whale sharks that utilise the Al Shaheen area using satellite-linked tags
Whale sharks rarely ventured into areas shallower than 40 m and no transmissions were made from water shallower than 20 m
Summary
The world’s largest fish, the whale shark, Rhincodon typus (Smith, 1828), has routinely been described as enigmatic [1,2], as aspects of its biology and habitat use remain poorly understood. Whale sharks routinely move across international boundaries and political jurisdictions [5,6,7,8,9]. Whale sharks can show a significant degree of site fidelity. Berumen et al [5] tagged 47 sharks in the southern Red Sea for periods of 11 to 315 days, with only eight sharks swimming farther than ~800 km from the tagging location. Passive acoustic tagging studies off Mafia Island in Tanzania demonstrated high whale shark residency to a small embayment for periods of up to two years [10]
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