Sunday, February 28, 2010
White Sharks - at the Cafe or at the SOFA?
White sharks (as in “Great White”) capture our imagination. Jaws certainly did not help their image. Nemo might have marginally redeemed them, but regardless of either movie, these are charismatic megafauna and the more we learn about them, the more interesting they become.
But how little we know – DNA data suggests that the N. Pacific population is largely separate from the sharks of South Africa, Australia, or the Atlantic. And though the world wide population of white sharks is more than just a few hundreds of sharks, the entire North Pacific adult population might be just that, with numbers more like the endangered monk seals than other reef animals.
One of the current interesting controversies centers on where White sharks go and what they do over the course of a year. Tracking data shows that there are at least two important aggregation sites on the west coast of the Americas, one at the Farallon Islands off California and one near Guadalupe Island off Baja, Mexico. Sharks do not seem to go from one of the aggregations sites to the other, but they do all head out into the Pacific midwinter, and most end up about half-way to Hawaii, in a vast expanse of open ocean.
What is out there to hold their attention? They seem to be doing a lot of up and down diving from the tacking monitor data, but for what? It has been characterized as an “oceanic desert”. California researchers named the area the “Shark Café” and suggested that maybe mating went on there. Researchers from the Guadalupe Island shark group disagreed, noting the area was too large to bring efficient close contact and named the area the SOFA (shared oceanic foraging area).
Oceanographic data suggested it did not appear to be an upwelling zone with nutrients and lots of fish, in fact it is a down-welling area if anything. But a cruise to the area revealed the presence of sperm whales, birds and on the one night they could fish, they caught Architeuthis (giant squid) and flying squid, both ready to spawn. So it is obviously not an “oceanic desert.”
Some compromised by saying maybe the SOFA was in the Café. Of course this would put a larger foraging area in a smaller mating area (and “the Café is in the SOFA ,” just does not sound right - sometimes acronyms get confusing). So stay tuned – further research will undoubtedly reveal what exists of such interest to white sharks - halfway to Hawaii.
For more information see: http://www.topp.org/species/white_shark for the California group, see: http://www.marinecsi.org/index.html
Posted by HIMB CEP at 6:00 PM