St. Helena: An Important Reproductive Habitat for Whale Sharks (Rhincodon typus) in the Central South Atlantic

Cameron T Perry,Kenickie Andrews,Beth Taylor,Leeann Henry,Annalea Beard,Simon J Pierce,Rhys Hobbs,Rafael De La Parra,Elizabeth Clingham,D Harry Webb,Gonzalo Araujo,Alistair D M Dove,Alistair D M Dove

doi:10.3389/fmars.2020.576343

Abstract

A reliable aggregation of whale sharks (Rhincodon typus) takes place in waters surrounding the remote South Atlantic island of St. Helena from December to May each year, peaking in January. A total of 277 individual sharks were identified over the course of the study, consisting of a 1.1:1 sex ratio of mature male and female sharks estimated to be between 5-12 m in total length. The SOCPROG best fit models estimated ~102 individual whale sharks at any one time with a decline to complete absence at ~75 days and an interannual periodicity for some sharks returning each season. Eyewitness accounts of mating behavior have been reported by reliable local observers on two separate occasions, which comprise the first observations of copulation in this species and are consistent with the size and sex demographics of the population. Horizontal movements away from the island proved difficult to track, due to extraordinarily deep-diving behavior that either damaged or caused premature detachment of the archival satellite tags, however, some individuals showed large scale movement away from the island towards both Africa and South America. Acoustic telemetry showed that animals use the habitats around the entire island, but are focused on the leeward side, particularly from James Bay to Barn Cap. Due to its likely role in the reproductive ecology of the whale shark, St. Helena represents a critical habitat for this endangered species and deserves concerted research efforts.

Highlights

The whale shark (Rhincodon typus) can be found circumglobally in tropical and warm temperate seas, and often forms reliable coastal aggregations, typically in response to high prey abundance (Rowat and Brooks, 2012)
Understanding the ability of whale shark populations to recover from these declines is vital for the conservation of the species, but little is known about their reproduction and some life-history characteristics
There is a lack of information about the biology and ecology of whale shark populations in the South Atlantic relative to other ocean basins (Norman et al, 2017)

Summary

Introduction

The whale shark (Rhincodon typus) can be found circumglobally in tropical and warm temperate seas, and often forms reliable coastal aggregations, typically in response to high prey abundance (Rowat and Brooks, 2012). Coupled with movement information from broad-scale whale shark photo-identification studies, such as Norman et al (2017), this indicates that whale sharks in the Atlantic represent a functionally separate population from those in the Indo-Pacific (Pierce and Norman, 2016). The lack of movement or genetic data form outside the Gulf of Mexico and Caribbean region within the Atlantic makes it difficult to identify finer-scale structure within this ocean basin. There is a lack of information about the biology and ecology of whale shark populations in the South Atlantic relative to other ocean basins (Norman et al, 2017). Data are lacking on the formation of coastal feeding aggregations of juvenile sharks in this region, which tend to occur in areas of seasonal upwelling (de la Parra Venegas et al, 2011) or other high-productivity habitats. The ecology of adult whale sharks, which are often sighted at volcanic islands far removed from continental shelf habitats (Ramírez-Macías et al, 2017), is poorly understood in general and in the Atlantic in particular

Methods

Results

Discussion

Conclusion