Tags reveal white sharks have neighborhoods in the north Pacific, say Stanford r...(The researchers used a combination of sa...)

Date:11/3/2009

>The researchers used a combination of satellite and acoustic tags to follow the migrations of 179 individual white sharks between 2000 and 2008. These sharks were adults or sub-adults that ranged in size up to 4,000 pounds, and were individually tagged at sites along the central California coast, including the Gulf of the Farallones, Tomales Bay and Ao Nuevo. The electronic tags reveal that the sharks spend the majority of their time in three areas of the Pacific: the North American shelf waters of California; the slope and offshore waters around Hawaii; and an area called the "White Shark Caf," located in the open ocean approximately halfway between the Baja Peninsula and the Hawaiian Islands.

"The thing we've learned about white sharks," said Scot Anderson, a marine biologist with the National Park Service, who has been involved in white shark research in Northern California for more than two decades, "is that they're not swimming around aimlessly they are very selective predators." Anderson is a coauthor of the paper.

Based on years of data demonstrating that the white sharks were homing with high fidelity back to California, the research team placed acoustic listening receivers on the ocean floor at sites thought to be high residency areas, or "hot spots."

By attaching 78 acoustic tags that create a unique "ping" or acoustic code for each tagged shark, the researchers were able to detect when the white sharks came within 250 meters (820 feet) of a receiver. This allowed the researchers to discern their pattern of coastal movements in high detail. The acoustic-tagged sharks spent time at four key sites along the central and northern California coast, each of which supports large colonies of seals and sea lions: Southeast Farallon Island, Tomales Point, Ao Nuevo Island and Point Reyes. The tags revealed that often sharks had favorite sites where they would remain resident for up to 107 days, although they occasionally would make brief
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Contact: Louis Bergeron louisb3@stanford.edu 650-725-1944 Stanford University Source:Eurekalert

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