Crittercams Provide Insights into Nurse Shark Behavior

Brian Handwerk and Mark R. Holmes
for National Geographic News
July 4 , 2002

Shark Photo Gallery: Go >>

Soon, the shark specialists and their crew will fold their tents, dismantle the observation platform, and wrap-up another successful research season. Though they may relish their return to the world of fresh food and hot showers, leaving brings up mixed emotions.

Jeff Carrier, a biologist at Albion College in Michigan, and Harold "Wes" Pratt, a biologist with the National Marine Fisheries Service, have come to this remote cove in the Florida Keys for the last 12 years to study nurse shark breeding and behavior.

Carrier is reflective as another successful expedition comes to a close. "You know, it's all an adventure," he says. "It's all exciting. We're sitting in a pristine area of the tropics, surrounded by wildlife, and we're looking at what is probably how Florida used to be."

Breeding Ground for Sharks, Science

Carrier and Pratt have been able to fill in some of the blanks about the growth, maturation, and life cycles of nurse sharks because they are able to capture the same animals year after year.

They've discovered that the nurse sharks in the Keys breeding grounds grow 3 to 5 inches (8 to 13 centimeters) a year, and don't reach sexual maturity until they are 18 to 24 years old. Such a slow reproductive cycle can become a problem if species populations are depleted by natural or human occurrences.

Other findings shed some light on the still-mysterious processes of shark breeding and mating behavior.

Wes Pratt calls nurse sharks the "couch potatoes" of sharks because they don't migrate like many other species. "They're born here in a tropical paradise, so why would they leave? But this sedentary nature creates a potential genetic problem," he said.

Carrier agreed. "When you consider the fact that they don't migrate, how in the world can these animals maintain genetic diversity without seeing the negative effects of inbreeding?"

Using DNA analysis, the scientists have determined that a female's litter of 25 to 35 pups can contain the offspring of four or five different male sharks. This may be a natural adaptation that helps to maintain the population's genetic diversity. "It's a strategy that helps remove the inbreeding problem," said Carrier.

Continued on Next Page >>




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