Seasonal Occurrence, Horizontal Movements, and Habitat Use Patterns of Whale Sharks (Rhincodon typus) in the Gulf of Mexico

Eric R Hoffmayer,Jennifer A Mckinney,Jill M Hendon,James S Franks,Michael E Byrne,Brett J Falterman,Benjamin Galuardi,William B Driggers

doi:10.3389/fmars.2020.598515

Abstract

In the northern Gulf of Mexico (GOM), whale sharks (Rhincodon typus) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and shelf-edge waters (81%) whereas tag data revealed the sharks primarily inhabited continental slope and open ocean waters (91%) of the GOM. Much of their time spent in open ocean waters was associated with the edge of the Loop Current and associated mesoscale eddies. During cooler months, there was a net movement southward, corresponding with the time of reduced sighting reports. Several sharks migrated to the southwest GOM during fall and winter, suggesting this region could be important overwintering habitat and possibly represents another seasonal aggregation site. The three long-term tracked whale sharks exhibited interannual site fidelity, returning one year later to the vicinity where they were originally tagged. The increased habitat use of north central GOM waters by whale sharks as summer foraging grounds and potential interannual site fidelity to Ewing Bank demonstrate the importance of this region for this species.

Highlights

Our understanding of the ecology of large marine vertebrates has increased significantly in recent years due to advances in bio-logging technology to study their movements, behavior, physiology and habitat preferences (Hart and Hyrenbach, 2009; Jaine et al, 2014; Chmura et al, 2018; Whitford and Klimley, 2019)
Whale sharks were reported from continental shelf and slope waters throughout the northern Gulf of Mexico (GOM) with most reported observations occurring from the DeSoto Canyon to waters off Corpus Christi, TX, with some of the highest concentrations occurring in areas in the north central (NC) GOM, in waters surrounding Ewing Bank, and offshore of Tampa Bay
Eighty-one percent of the sightings locations occurred in continental shelf and shelf edge waters with only 19% of the sightings occurring over continental slope and open ocean waters

Summary

Introduction

Our understanding of the ecology of large marine vertebrates has increased significantly in recent years due to advances in bio-logging technology to study their movements, behavior, physiology and habitat preferences (Hart and Hyrenbach, 2009; Jaine et al, 2014; Chmura et al, 2018; Whitford and Klimley, 2019) Migratory fishes, such as pelagic sharks, have been difficult to study due to the complexity of their ecology and the concealing nature and remoteness of their environment. Whale shark occurrence has been correlated with high abundance of prey in coastal areas (Heyman et al, 2001; Rohner et al, 2015, 2018) and productive frontal zones and large-scale spawning events in offshore waters (Hoffmayer et al, 2005; de la Parra Venegas et al, 2011; Ryan et al, 2017)

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Conclusion