Scientists Study Nurse Shark Mating Habits

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

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In the remote islands of the Florida Keys, Jeff Carrier and Harold "Wes" Pratt are studying sharks. Again. They've spent much of the past 30 years delving into their underwater world, to gain a better understanding of what Pratt calls "the ultimate form of marine life."

It's a never-ending learning process, one Carrier undertakes in the spirit of John Steinbeck, who mused in The Log from the Sea of Cortez: "The true biologist deals with life, with teeming boisterous life, and learns from it. Learns that the first law of life is living."

"When we observe nature," Carrier explained, "and all the wondrous aspects of life, the survival strategies that work the best are those that give animals a survival edge. Everything that they do is geared toward giving them the best chance to survive in their habitats, and it's a wondrous thing to see."

In the Keys, the ongoing cycle of survival can be seen each year at the site that serves as the breeding grounds of the nurse shark.

The sharks return annually to these same grounds, and the researchers return with them. It's Carrier and Pratt's twelfth straight year on the site, where Carrier estimates that he has caught, studied and tagged some 1,500 nurse sharks over the past 30 years.

Ancient Breeding Grounds

The hard work of these marine biologists is part of a unique, long-term study of the breeding and social habits of these animals. Such lengthy and detailed studies are a rarity in the world of shark research, in which the subjects are not always easy to track down.

The Keys-area nurse sharks, however, are easy to locate. Unlike other species, they don't migrate and they prefer shallow coastal waters. They return to the same breeding ground each year, and the scientists follow to study their mating behaviors. According to historical reports, however, the sharks have been around the area much longer than modern science.

Breeding nurse sharks were reported in the same Keys mating grounds as early as 1860, and may have been there long before that time. This kind of patterned behavior provides a clue to the challenge of understanding the sharks' mating processes, and the relationship that they have with the habitat itself.

"What is it about that site that's so important to the species?" asked Carrier. "It's not just nurse sharks returning to this site, it's the same specific animals, year after year. So there is something enormously important here about site fidelity that we're trying to understand."

Continued on Next Page >>




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