Abstract:
328 whale sharks (Rhincodon typus) were identified using photographs and pattern recognition software between 2013 and 2017 around the island of St Helena in the South Atlantic. The highest number of whale sharks were recorded in the month of January. This is probably due to the sharks exploiting a seasonally abundant food source, such as tuna (Scombridae spp.) and other fish spawn in the waters around St Helena. Other behaviours observed included females remaining stationary in an inverted arc posture with males swimming around them, which is associated with mating behaviour in other shark species. The mean total length of the sharks was 7.63 metres, and of the sharks whose sex was determined 45.9% (133) were female, and 54.1% (157) male. Of those males, only one was juvenile as determined by clasper morphology. Worldwide, aggregations of whale sharks tend to consist of majority juvenile males. The combination of mature male and female whale sharks in the study area and the observed courtship behaviour means it is possible that the waters around St Helena are of global importance for whale shark mating.
The St Helena aggregation was compared to an aggregation in the Maldives with 315 whale sharks identified over 10 years. Whale sharks in the Maldives bore a significantly higher injury rate (82.2%, p<0.001, X2 test) than those in the St Helena aggregation (9.1%), with anthropogenic injuries in Maldives at 54.9%, compared to 2.4% in St Helena. This may be a consequence of the greater number of weakly regulated ecotourism boats targeting the Maldives aggregation compared to the tightly regulated and limited ecotourism for whale sharks around St Helena.
