Cape Town - Researchers are butting heads over the number of white sharks along the South African coastline, with some believing that the population is stable and has moved from the coast of the Western Cape to the Eastern Cape coast to escape predatory orcas, accounting for some of the rare sightings along the western coastline.
New research, however, refutes this, saying that uncertainty remains for the white shark population as the stability and redistribution cannot be concluded by the previous researchers.
Dr Sara Andreotti, a marine biologist in the Department of Botany and Zoology at Stellenbosch University and one of the co-authors of the new research, said they are worried about the effect of the narrative on conservation efforts.
“There is no evidence of the hundreds of white sharks counted in False Bay, Gansbaai and Mossel Bay 10 years ago aggregating now somewhere else along the South African coastline. Our concern is that unsupported claims of population stability could jeopardise conservation actions urgently needed for white sharks,” she warned.
Research published in September last year concluded, among other things: “Although it is encouraging that there is no evidence of a population decline for this species across their entire South African range, changes in geographical distribution need to be closely monitored due to their socio-economic impact on cage diving activities, tourism and risk of humanshark incidents, as well as ecosystem effects on fish community structure.”
However, in new research published recently, a group of concerned marine biologists highlighted several issues with the methods and inferences made in the study and argued “that the data, as currently analysed and interpreted, cannot support the claims made about population stability, nor redistribution, of South Africa’s white sharks”.
The researchers, led by Dr Enrico Gennari, director of the Oceans Research Institute, said they felt obliged to raise the concerns “given what it means for management”.
“If the white shark’s population is stable, there is no need for concern. However, if the declines in white shark sightings seen in former hot spots are actually representative of the population, then conservation action is urgently needed.”
In the earlier research led by Heather D Bowlby from the Fisheries and Oceans Canada at Bedford Institute of Oceanography in Canada, the researchers said substantial declines in white shark presence at two primary aggregation sites have raised concerns about the species’ status throughout South Africa.
“Using the most comprehensive suite of abundance indices compiled to date, we evaluated temporal trends and the strength of evidence for regional redistribution. Individual indices from all primary aggregation sites in South Africa were highly variable. The overall temporal trend from a log-linear generalised additive model was relatively flat, indicating largely unchanged abundance throughout South Africa since protection in 1991.
“However, reports of human-shark incidents showed a general shift from the Western to the Eastern Cape.”
Gennari disagrees and objected to the claim that South Africa’s white shark population has migrated eastwards.
“The first objection has to do with the presentation of the two datasets in 2023, and that one cannot infer that an increase in the number of shark sightings in one spot, in this case Algoa Bay, is directly comparable to a reduction in shark sightings in another spot, such as False Bay.”
The group of concerned marine biologists urged authorities such as the Department of Forestry, Fisheries and the Environment to take a precautionary approach in light of the declines in white shark sightings from their historical hot spots, and the consequent negative impact on South Africa’s ecotourism economy.