Wednesday, November 4, 2009

The Great White (Pacific) Shark - Savage of the . . . buffet line?

Today’s Washington Post on-line edition contains one article worth reading – Juliet Eilperin piece on Pacific (Great) white sharks. Eilperin’s article is a summation of the longer scientific piece published in the Proceedings of the Royal Society B(iological Science) that looks at a decade of acoustic tagging and tracking of Pacific White sharks. And for us marine science types, it’s really cool.

First, though, a word about names – white sharks are technically named for the basin in which they occur, not a “Great.” In fact, all white sharks world-wide share the same scientific name (Carcharodon carcharias), and then scientists generally add the basin to the name. Thus the article refers to Pacific white sharks, to denote those members of this species found in the Pacific Ocean.

Second, the researchers who published the Royal Society article have made a major break through in the understanding of white shark behavior. It seems, again based on a decade’s worth of tagging, tracking, and genetic analysis, that white sharks spend the majority of each year cruising the west coast of the continental U.S. From a biological perspective, its easy to understand why – that coast is a veritable predator’s buffet of fatty seals and sea lions (and salmon) which can help feed a hunger shark well for a long time.

It also seems that the sharks swim en masse out to Hawaii every year, both for mating purposes (!) and for additional feeding. That later part actually comports with several scientific studies on endangered Hawaiian monk seals – who face a threat from general shark predation on pups that may be limiting recovery of the seal population.

Now, the most fascinating part of the use of these locations is that individual sharks have tremendous site fidelity – meaning they come back to the same places year in and year out. Salmon exhibit similar behavior in returning to their birth streams to spawn, and all species of sea turtles exhibit site fidelity when choosing beaches on which to lay their eggs. So in the marine animal world, this isn’t new.

What these finding do suggest, however, is that white sharks probably learn what the ecology of their “territory” is, and that when humans alter that ecology we run the risk of increasing our interactions with white sharks (including infamous shark bite episodes). The research also suggests that white shark presence and site fidelity might just be good indicators of ecosystem health, because one can assume that an adult white shark will alter its migratory and feeding behavior if food sources change.

The bottom line, then, is that white sharks are for more fascinating then even shark biologists previously thought. They like having a ready “buffet” to cruise just as much as we humans do, and we might be able to harness them (or at least their presence) to help define and understand large swaths of our coastal ecology.

1 comment:

jg said...

Excellent post. Thank you.