25 January 2006

White Shark taggers team up for TOPP (Tagging of Pacific Pelagics)

The blue whale carcass undulated with the swell, a huge, pale and nutrient-packed spread for the hungry denizens of top predators patrolling the waters around the Farrrallon Islands. A gift from the sea to Scot Anderson of the Point Reyes Bird Observatory, who works the area each fall, identifying and tagging white sharks...

Ever mindful of safety, Anderson is often conservative in his evaluations of tagging conditions. That morning, he'd made a tough call, opting not to head out into the winds, but the carcass sighting shifted the equation just enough to make the journey worthwhile. A dead whale is the ultimate shark buffet and a taggers' dream.

With such an enticing and enormous meal at hand, Anderson's team could tag a feasting shark directly from the Derek M. Baylis (a 65-foot sailboat frequently used by the Monterey Bay Aquarium), rather than brave the swells on their tiny skiff. A lucky break for TOPP's team of scientists from Stanford University, the University of California, Davis, the Monterey Bay Aquarium, and the Pelagic Shark research Foundation.

For 20 years, Stanford's Dr. Barbara Block has led physiological and tagging studies of sharks, particularly those in the lamnid family, an evolutionary intriguing group which includes white sharks, salmon sharks and makos. Like bluefin tunas, many sharks in this family are endothermic, with circulatory systems configured to retain metabolic heat and help warm powerful swimming muscles.

Also like the tunas, lamnid hearts are specially adapted to perform effectively while pumping blood that is chilled to ambient water temperature during passage through the gills.

While salmon sharks appear to be the most endothermic of the lamnids, TOPP has discovered that white shark habitat spans a surprisingly large range of temperatures. Scientists have conducted few studies on the internal temperatures of white sharks, so it remains an open question just how endothermic this species actually is.

But it is known that during the fall, the northern California off-shore waters favored by the white shark often hovers in the low to mid 50s F, a far cry from the balmy subtropical waters these large sharks appear to frequent during the winter and spring.

While the white shark is a media favorite and pop-culture icon, from a scientific perspective, very little is known about the largest of TOPP's sharks. Less than a decade ago, the white shark was thought to be coastal. So when the team of scientists from Block’s lab and the Point Reyes Bird Observatory placed a PAT tag on a Farrallon-tagged shark called Tipfin only to have it surface near Hawaii, jaws dropped at Stanford and elsewhere.

A study published in 2005 documented an even longer journey, with a white shark traveling from Africa to Australia and back again. Ongoing tag-based studies of white shark migration are providing more detailed information about these long-distance migrations. For instance, TOPP currently boasts a one-year archival tag record for a white shark, which has given scientists high-resolution data on the animal's second-by-second activity.

TOPP's adult white shark tagging pools the efforts of four teams led by expert shark taggers working in disparate sites that are all highly productive and play home to large pinniped rookeries. On a map, Point Reyes to the north of San Francisco, the Farrallon Islands to the west, and Ano Nuevo just north of Santa Cruz form a triangular region historically well-known to locals for white sharks.

Each area also had resident white shark tagging and observation programs operating for the most part – independently. Thanks to TOPP PI Barbara Block's effort, the four shark teams overseeing these programs are now partnering and the union promises to yield an enormous payoff in valuable data about one of the oceans most famous—and least understood predator.

The TOPP shark teams are diverse, yet all are eager to help fill the enormous gaps in knowledge about white sharks. Where do they go when they leave the coast? What do they eat? Where do they breed? How large is their range, and how many of these animals are there? These are only some of the questions addressed by the researchers whose profiles follow.

Read profile of TOPP white shark tagger Scot Anderson
Read profile of TOPP white shark team leader Pete Klimley
Read profile of TOPP white shark tagger Sean Van Sommeran

Source: www.divenews.com


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