False Bay: Ladies Only!
A terrific breakthrough was recently made by South African shark scientists working in the False Bay region.
The recent discovery has determined that, should you happen upon a white shark in the inshore area in False Bay this summer, and, during your encounter with one of the deadliest predators known to man, find yourself pondering the sex of this particular animal, you can now be fairly certain that it would most likely be of the feminine variety.
Cape Town shark scientist and research manager of the city’s Shark Spotters programme, Alison Kock, and her team recently made significant findings and published it in an online journal PLOS ONE (Public Library of Science). They conducted a study by tagging 56 sharks, male and female, in the False Bay area and tracked their movements over a period of 32 months.
While it is well known that seal colonies are well established white shark aggregation areas, the new study found that white sharks seem to frequent inshore areas during the summer months and that these areas form an equally important part to the habits of this apex prowler of the deep. Furthermore, and perhaps most fascinating of all, there seems to be a pattern of segregation between male and female white sharks during the summer months; where the females apparently shift to the inshore areas while it is unclear as to where the males travel.
“We found that white sharks showed high levels of residency to the seal colony over autumn and winter as expected, but we were very surprised to learn that female sharks showed equally high residency at inshore areas during spring and summer – while males were notably absent,” said lead author Alison Kock. “The shift from the island in autumn and winter to the inshore region in spring and summer by female sharks mirrors the seasonal peaks in prey abundance including juvenile seals at the island in winter and a range of migratory fish along the inshore during the warmer months,” Kock elaborated. The research ultimately shows that white sharks – and especially females – are at risk because of their frequent use of inshore areas of False Bay. Fishing, pollution, and damage to natural habitat from coastal development are all factors contributing to the fast diminishing numbers of white sharks.
Conservation of white sharks is a global issue and these beautiful predators are increasingly threatened. If it was ever doubted that this species is under threat, the evidence of tagged white sharks being killed for their fins in Mozambique — among other places — should make it clear that laws need to be enforced to curb the killings. The shark research team, OCEARCH, tagged a 3.6 metre female in Mossel Bay in March last year and dubbed it Brenda after the late Brenda Fassie. In October 2012, Brenda’s OCEARCH tracker ‘pinged’ inland somewhere south of Guinjata. On closer inspection it was confirmed that Brenda had been captured and killed off the coast of Mozambique. She was caught in a gill net and was harvested by village fishermen who then gave the meat to the village and sold the fins, presumably to the highest bidder. Two more white sharks were reportedly killed in January of this year in Inhambane Province and their fins allegedly sold to Chinese buyers.
Ryan Johnson, chief scientist for the OCEARCH tagging expeditions underscored the importance of regional cooperation: “Brenda’s capture in Mozambique was a tragic illustration of a very real truth about Africa’s large migratory sharks, that is, they do not respect national marine boundaries. For this region to effectively conserve sharks we require strong and continued regional cooperation between nations.” While international protection for sharks remains a problem, the Shark Spotters programme in Cape Town aims to conserve the volatile white shark population of False Bay. Research producing scientific breakthroughs such as the discovery of the different migratory patterns of males and females and the tendencies of females to move inshore during summer, goes a long way to improve our understanding of these highly mysterious creatures and therefore betters our chances of conserving them more efficiently. Furthermore, Shark Spotters’ main undertaking is to mitigate the ongoing shark-human conflict, and the fact that we are now aware of the increased presence of female white sharks in the inshore areas during certain months of the year, will improve strategies in the mitigation process.
Although the study is focused locally, its findings have broad conservation and management implications because it highlights the need for understanding how behavioural patterns differ between sexes of the same population as this can influence a particular sex’s susceptibility to threats. Co-author, Justin O’Riain, associate professor of behavioural ecology at UCT welcomed the findings as an important contribution to the broad field of predator spatial ecology, “We have a wealth of such information for land predators and these results provide an important step in narrowing the knowledge gap between marine and terrestrial systems and assessing the extent of our generalities”.
