Girls only in summer for False Bay sharks
SCIENCE & TECH / 29 Jan '13, 10:41amBy: John Yeld
Cape Town - Boys going down to the beach in summer to hang out with the girls would be the natural order of things, one would imagine – but when it comes to white sharks, the exact opposite is true.
This is what exciting new research by South African scientists working in False Bay has shown.
While all the individuals of this species congregate together off Seal Island during autumn and winter – behaviour that is well known – what has now been confirmed for the first time is that female white sharks show very high residency at inshore areas such as the Muizenberg-to-Fish Hoek coastline during spring and summer, while the males, of all ages, are almost entirely absent.
This research, published in the online open-source research journal Plos One (Public Library of Science), has important implications for the conservation of this threatened apex predator and for managing the interplay between sharks and people to try to avoid or minimise attacks, says lead author Alison Kock.
Kock, who is completing her PhD at UCT and is research manager of the city’s Shark Spotters programme, said the study had been carried out in False Bay, where she and fellow researchers had tracked 56 white sharks fitted with electronic tags over 32 months. The sharks were of both sexes and ranged in length from 1.7m to 5m.
White sharks “showed high levels of residency (around) the (Seal Island) 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, and that males were notably absent”, Kock said
The shift from the island in autumn and winter to the inshore region in spring and summer by the females mirrored 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 added.
Their study confirmed False Bay as a critical area for white shark conservation, and that female sharks were particularly at risk because of their frequent use of the inshore areas of the bay that were affected by fishing, pollution and damage to natural habitat from coastal development.
“Furthermore, the finding that female sharks frequent the inshore regions during spring and summer when recreational use peaks highlights the need for ongoing shark-human conflict mitigation strategies such as the Shark Spotter programme,” Kock said.
The Shark Spotters aim to improve public safety while simultaneously conserving this vulnerable shark population.
Co-author, Justin O’Riain, associate professor of behavioural ecology at UCT’s zoology department, welcomed the findings.
“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”.
White sharks are threatened apex predators and despite South Africa enacting protective legislation in 1991, there is limited knowledge available on how best to make such protection effective.
* On the web: http://dx.plos.org/10.1371/journal.pone.0055048