Interactions Between the Great White Shark, Carcharodon Carcharias, and Chumming Vessels in Mossel Bay, South Africa

Résumé du livre

The correlation between shark cage-diving using the method of chumming to lure white sharks and the increase in shark attacks on human has been very controversial for this last few years. Seal Island at Mossel Bay, South Africa, shelters a 4000 Cape Fur Seals (Arctocephalus pusillus pusillus) colony and its waters are consequently a highly frequented area by white shark that feed on it. Shark cage-diving activity had grown up fast these last years in the Western Cape and offer shark viewing and cage-diving. But recently the surfer community and some scientists decided to ban cage-diving activities and their practice of chumming believed to be the cause of shark attacks on human by conditioning them to associate human and boat with food. If all the good common sense is of one accord with these suspicions, it seems necessary to evaluate the effective influence of these practices on aggregation and distribution of white sharks in the bay before ban them. The present study, conducted within the framework of the PhD of Mr. Ryan Johnson (University of Pretoria) in Mossel Bay, gives some preliminary answers to this question. A particular attention was paid in behavioural changes of individual white sharks relatively to potential conditioning by these activities. This study was conducted in parallel with the two types of vessels. The use of photo-identification permitted to individualize and recognize present white sharks in the study area and to gain information in their visit patterns at the vessels. Individuals were tagged by acoustic pingers permitting to follow them by acoustic telemetry such as listening stations or manual tracking. Aerial surveys and surveys of predation events on seals were conducted in order to investigate distribution patterns and occurrence around Seal Island.