Sunday, February 20, 2011

Florida's Shark Congregation: sharks swarm in the shallows prior to northern migration

Each year, around this time, blacktip and spinner sharks congregate off the southeast coast of Florida as a prelude to a northerly migration. And this year was no exception. Sharks numbering in the hundreds, if not thousands, were observed off Palm Beach, getting within 100 yards of shore.

In this area, you have a white sandy bottom that is shallow and extends quite a ways out to sea. Against this bright backdrop, the sharks, with their darker coloration on the tops of their bodies, stand out quite clearly, as seen by this helicopter video taken for Florida's Sun-Sentinel.

The sharks will move as far north as Chesapeake Bay, feeding on migrating schools of baitfish like mullet. Scientists who study animal migrations are always curious as to what might be the motivating factor for a particular migration. Is it due to a change in climate or water temperature? Or to find suitable mating grounds? Or is it following a particular food source. That appears to be the case with these sharks off of Florida - simply gravitating where the hunting is good.

Blacktip (Carcharhinus limbatus) and spinner sharks (Carcharhinus brevipinna) are not considered particularly dangerous sharks. However, in Florida they have been implicated in as many as one-third of Florida's total number of attacks. But with these attacks, poor visibility and mistaken identity are the root causes.

"These are not really aggressive species," said Brent Winner of the Florida Fish and Wildlife Conservation Commission. "But if the water is murky and you see hundreds of sharks, you probably should stay out of the water. Even though they don't eat people, the chance of being bitten is there."

First, you need a hungry shark, one who is on the hunt. This is a critical first step as these sharks do not bite just for the fun of it. Then you add in reduced visibility in the shallows as that white sand I mentioned earlier gets stirred up in the surf. The shark is looking for a small fish, and the flash of white from a human hand or foot - particularly if aided with gold or silver jewelry which can look like sunlight dancing on fish scales - can cause the shark to make a quick dash and grab. Of course, as soon as it realizes its prey does not taste like a fish, it quickly moves on its way. But the result is there's now a new statistic for the shark-human interaction record books.

When I see footage of these shark migrations, it don't view it with any sense of alarm, regardless of how the media portrays it. It's good to see these congregations and the only fear should not be directed at the sharks but at any unscrupulous fisherman who views it as an easy catch.

Read about the migration in the