Saturday, November 07, 2009

Northeastern Pacific Ocean: Isolated migrations of Great White sharks have been discovered

In a new research, scientists have found that the migratory behaviors of the white shark has lead to the formation of isolated populations in the northeastern Pacific Ocean that are genetically distinct from sharks elsewhere in the world.

White sharks are a large, highly mobile species, said Salvador Jorgensen, a postdoctoral scholar at Stanfords Hopkins Marine Station.

They can go just about anywhere they want in the ocean, so its really surprising that their migratory behaviors lead to the formation of isolatedpopulations, he added.

Scientists with the Tagging of Pacific Predators (TOPP) program combined satellite tagging, passive acoustic monitoring and genetic tags to studywhite sharks popularly known as great white sharks in the North Pacific.

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 Ano 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 calledthe White Shark Caf, located in the open ocean approximately halfway between the Baja Peninsula and the Hawaiian Islands.

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 thewhite 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 tags revealed that often sharks had favorite sites where they would remain resident for up to 107 days, although they occasionally would make brief visits to the other nearshore hot spots.

Also, genetics techniques were used to examine the relationships of the California sharks to all other white sharks examined globally.

Studies of maternally inherited mitochondrial DNA sequences show that the populations are distinct, and suggest that the northeastern Pacific population may have been founded by a relatively small number of sharks in the late Pleistocene within the last 200,000 years or so.

According to Molecular geneticist Carol Reeb, a research associate at Stanford, Even though we know they travel great distances, their paths are surprisingly constrained to specific routes. This explains how a highly migratory marine species becomes a genetically isolated population.


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