Scientists Take A Close Look at Basking Sharks

Basking sharks have been highly sought after for their fins, and because of this their population has been greatly diminished. The second largest fish in the ocean, second only to the whale shark, the basking shark is now included on the Convention on International Trade in Endangered Species, and are considered vulnerable to endangered. Scientists have little information about the species, and are working toward changing that. In order for conservation efforts to be effective some very basic knowledge is needed about the species including mating, birthing and where the animals spend their time. Scientists have very little knowledge regarding any of this as the animals disappear for nearly half the year, and juveniles and pregnant females have never been spotted. Through genetic studies scientists off Cape Cod, Massachusetts recently found that basking sharks worldwide are fairly closely related. Tagging studies are being conducted over the summer months off Cape Cod where the animals spend time feeding on the abundant levels of zooplankton present during the warmer months. The tags can remain on the sharks up to a year, recording light levels, the depths to which the sharks dive, and seawater temperatures. A tag is programmed to pop off at a specific time, and once it floats to the surface, it transmits these data back to scientists on shore. Simon Thorrold, a biologist at Woods Hole Oceanographic Institution is working with colleagues who have shown that some sharks are migrating to sunnier locations thousands of kilometers away during the winter months. Once they move off the continental shelf of the U.S. East Coast, which is about 150 meters or 490 feet deep, the sharks dive down to 800 to 1,000 meters (2,600 to 3,300 feet), spending up to months at a time at depth in the tropics. This may be where pregnant females and pups reside. Transequatorial migrations may also result in an interbreeding worldwide population.