Whitetip Shark Migrations Lead Them Home To Bahamas
February 21, 2013

Wandering Whitetip Sharks Stick Close To Home In Bahamas

Brett Smith for redOrbit.com - Your Universe Online

As their name indicates, oceanic whitetip sharks (Carcharhinus longimanus ) are best known as inhabitants of the open seas. However, a new report by an US-led team of marine biologists has found that the deadly apex predators regularly migrate to waters around the Bahamas.

Because the sharks were also found prowling for hundreds of miles in the waters around the Atlantic island nation, the biologists say their study could have implications for shark conservation strategies on an international level.

"While the oceanic whitetip shark is one of the most severely overexploited shark species, it is also among the least studied because it lives much of its life far from land in the open ocean," said the study´s lead author Lucy Howey-Jordan, from the scientific tracking company Microwave Telemetry, Inc. "Before this study and our ongoing research, very few of these sharks had been fitted with satellite tags, and the data we obtained will help establish new conservation measures."

According to their report in the online journal PLOS ONE, the team attached tracking tags to one male and 10 female mature oceanic whitetip sharks near the Bahamas in May 2011 and recorded the sharks´ behavior over several different intervals. The tags transmitted their depth, water temperature and location for pre-programmed periods of time.

The team found that five of the sharks made long-distance travels far away from the chain of tropical islands, with one even traveling as far out as Bermuda. All of these were mature female sharks that eventually returned to the Bahamas, providing the first evidence of return-migration for these large marine predators.

The researchers also found that the sharks spent about 68 percent of their time in Bahamian waters, which is good news for conservationists since the Bahamas have strictly protected the sharks for the past two decades.

"The Bahamian government had the foresight to protect these and other species of sharks within their waters, starting with the longline fishing ban in early 90s, and culminating with the more recent shark sanctuary initiative," said co-author Edward Brooks, program manager of the Shark Research and Conservation Program at the Cape Eleuthera Institute.

"This level of protection is vital for the continued existence of these important apex predators, and I hope that the example set by The Bahamas will encourage other nations to follow suit." Because the sharks often roam away from the protected waters of the Bahamas, they are vulnerable to unscrupulous fishermen who prize the whitetips for their valuable fins.

"Oceanic whitetips frequently take bait meant for other species like tuna and swordfish," co-author Demian Chapman, an assistant director of science at the Institute for Ocean Conservation at Stony Brook University, told BBC News. "Fisherman will take all of these sharks that were incidentally hooked and they will take their fins, and that is fatal to the shark."

"If we want to continue to see these animals in our oceans, fishing nations will have to work together to protect this species, and monitoring of trade and enforcement measures will need to be coordinated on an international level,” he added.

In future studies, the marine biologists say they will focus on finding out the reason behind the sharks´ migrations. By using ultrasound scanners and hormone testing, they plan to see if the pattern is related to the animal´s two-year reproductive cycle.