Abstract
Whale sharks, Rhincodon typus, aggregate by the hundreds in a summer feeding area off the northeastern Yucatan Peninsula, Mexico, where the Gulf of Mexico meets the Caribbean Sea. The aggregation remains in the nutrient-rich waters off Isla Holbox, Isla Contoy and Isla Mujeres, Quintana Roo for several months in the summer and then dissipates between August and October. Little has been known about where these sharks come from or migrate to after they disperse. From 2003–2012, we used conventional visual tags, photo-identification, and satellite tags to characterize the basic population structure and large-scale horizontal movements of whale sharks that come to this feeding area off Mexico. The aggregation comprised sharks ranging 2.5–10.0 m in total length and included juveniles, subadults, and adults of both sexes, with a male-biased sex ratio (72%). Individual sharks remained in the area for an estimated mean duration of 24–33 days with maximum residency up to about 6 months as determined by photo-identification. After leaving the feeding area the sharks showed horizontal movements in multiple directions throughout the Gulf of Mexico basin, the northwestern Caribbean Sea, and the Straits of Florida. Returns of individual sharks to the Quintana Roo feeding area in subsequent years were common, with some animals returning for six consecutive years. One female shark with an estimated total length of 7.5 m moved at least 7,213 km in 150 days, traveling through the northern Caribbean Sea and across the equator to the South Atlantic Ocean where her satellite tag popped up near the Mid-Atlantic Ridge. We hypothesize this journey to the open waters of the Mid-Atlantic was for reproductive purposes but alternative explanations are considered. The broad movements of whale sharks across multiple political boundaries corroborates genetics data supporting gene flow between geographically distinct areas and underscores the need for management and conservation strategies for this species on a global scale.
Highlights
The whale shark Rhincodon typus is the world’s largest living fish and one of the most charismatic and unmistakable animals in the sea
Comparison of SPOT vs pop-up satellite archival tags (PSATs) through Double-Tagging In our double-tagging experiment, the application of first the UKFSST model and the bathymetric correction improved the accuracy of the PSAT location estimates substantially, as shown by a reduction in the root mean square (RMS) error of the most probable track (MPT)’s latitude and longitude (0.277u; 0.289u) compared to those of the raw geolocations (1.922u; 0.301u)
Movements into the Caribbean Sea Photo-identification data from our study showed a connection between whale sharks present in summer months off the YP and sharks observed during winter and spring off Belize (Gladden Spit) and Honduras (Utila Bay Islands), two areas with an active ecotourism trade for whale sharks and research programs that utilize photo-identification [1,25]
Summary
The whale shark Rhincodon typus is the world’s largest living fish and one of the most charismatic and unmistakable animals in the sea. Whale sharks are vulnerable to overexploitation due to their conservative life history, slow swimming speed and docility at the surface, and highly migratory nature [2]. This species is listed as ‘‘Vulnerable’’ in the IUCN Red List of Threatened Species [3] and is one of eight shark species currently listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Whale sharks travel long distances and the timing of their movements are typically associated with localized blooms of planktonic organisms and water temperature changes [1] The use of both pop-up satellite archival tags (PSATs) and near-real-time satellite tags (e.g. Smart Position or Temperature Transmitting satellite tags, SPOTs) has greatly expanded our understanding of the broad horizontal movements of R. typus in certain parts of its range. In the Gulf of California (GOC), Eckert and Stewart (2001)
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