In the past I have blogged about how the use of electronic tagging and tracking can support the conservation of marine animals. I have also addressed some misconceptions about shark tagging studies and discussed the value of such research for conservation. Building off these topics, I would like to share the results of two recently published shark satellite tracking studies that have implications for conservation management.To study their movements in relation to marine protected areas, satellite tags were affixed to the dorsal fins (left) of great hammerhead sharks, Sphyrna mokarran (top right), tiger sharks Galeocerdo cuvier (bottom right); Credit: Dorsal fin – Frank Gibson; Credit: Hammerhead and Tiger shark – Neil Hammerschlag, Ph.D.
The first study example, published in the Proceedings of the National Academy of Sciences tracked more than 100 sharks equipped with satellite tags from six different species in the North Atlantic while concurrently tracking 186 GPS-equipped longline fishing vessels. The results showed that commercial fishing vessels target shark hotspots (i.e. areas where sharks tend to congregate). These hotspots fell within international waters of the high seas were no protections exist for these sharks. As a result, these species are at high risk of being overfished.
About 80 percent of the range for two of the most heavily fished species tracked—the blue and mako shark—overlapped with the fishing vessels’ range. The study concluded that because current hotspots of shark activity are at particularly high risk of overfishing, the introduction of high seas conservation measures such as catch quotas, size limits or marine protected areas will be necessary to protect oceanic sharks that are commercially important.
The second study example, published in the journal Diversity and Distributions tracked the movements of 86 great hammerhead, bull and tiger sharks equipped with satellite tags in waters off south Florida and the northern Bahamas. The study compared the areas where the sharks were spending the majority of their time (core habitat use areas, CHUAs) against zones that prohibited fishing or were these sharks were already fully protected within areas of the U.S. and Bahamas exclusive economic zones (EEZs).
The results revealed that none of the tracked bull shark’s regional CHUAs were in areas that are fully protected from fishing, and for the great hammerhead and tiger sharks tracked, only 18 percent and 35 percent, respectively, of their core use areas were currently protected from fishing. However, the results showed that expansion of protected areas into U.S. federal waters would protect 100 percent of core home range areas used by three species of sharks tracked.
While there are concerns that marine protected areas may not benefit large sharks because they are wide ranging, this study suggested that conservation benefits can be achieved if sharks are protected in areas where they spend the majority of their time, such as their core habitat use areas.