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First Census Finds Surprisingly Few White Sharks Off Central California Coast; 219 'A Real Surprise'

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DAVIS, California -- In the first census of its kind, research led by UC Davis and Stanford University found that there are far fewer white sharks off central California than biologists had thought.

The study, published today in the journal Biology Letters, is the first rigorous scientific estimate of white shark numbers in the northeast Pacific Ocean. It is also the best estimate among the world's three known white shark populations (the others are in Australia/New Zealand and South Africa).

The researchers went out into the Pacific Ocean in small boats to places where white sharks congregate. They lured the sharks into photo range using a seal-shaped decoy on a fishing line. From 321 photographs of the uniquely jagged edges of white sharks' dorsal fins, they identified 131 individual sharks.

From these data they used statistical methods to estimate that there are 219 adult and sub-adult white sharks in the region. (White sharks are classed as sub-adults when they reach about 8-9 feet in length and their dietary focus shifts from eating fish to mostly marine mammals. They are adults when they reach sexual maturity for males, that is about 13 feet long; for females, it is about 15 feet.)

"This low number was a real surprise," said UC Davis doctoral student Taylor Chapple, the study's lead author. "It's lower than we expected, and also substantially smaller than populations of other large marine predators, such as killer whales and polar bears. However, this estimate only represents a single point in time; further research will tell us if this number represents a healthy, viable population, or one critically in danger of collapse, or something in between."

"We've found that these white sharks return to the same regions of the coast year after year," said study co-author Barbara Block, a Stanford University marine biologist and a leading expert on sharks, tunas and billfishes. "It is this fact that makes it possible to estimate their numbers. Our goal is to keep track of our ocean predators."

Satellite tagging studies have demonstrated that white sharks in the northeast Pacific make annual migrations from coastal areas in Central California and Guadalupe Island, Mexico, out to the Hawaiian Islands or to the "White Shark Caf," a region of the open ocean between the Baja Peninsula and Hawaii where white sharks have been found to congregate and then they return to the coastal areas.

In addition to Block and Chapple (who is now a postdoctoral researcher at the Max Planck Institute in Germany), the study's co-authors are Loo Botsford, professor, and Peter Klimley, adjunct associate professor, both of the UC Davis Department of Wildlife, Fish and Conservation Biology; postdoctoral researcher Salvador Jorgensen of Stanford University (who is now a research scientist with the Monterey Bay Aquarium); researcher Scot Anderson of Point Reyes National Seashore; and graduate student Paul Kanive of Montana State University in Bozeman.

The research was funded by the National Oceanic and Atmospheric Association (NOAA) Fisheries through the Partnership for Education in Marine Resource and Ecosystem Management (PEMREM) and the NOAA Fisheries/Sea Grant Fellowship Program; the Gordon and Betty Moore Foundation; the National Park Service's Pacific Coast Science and Learning Center; Monterey Bay Aquarium; UC Davis Bodega Marine Laboratory; and Patricia King, a member of the Point Reyes National Seashore Association.

Views expressed in this article do not necessarily reflect those of, its staff or its advertisers.

Reader Comments

3 people have commented so far. cloud add your comment

A few points about this study. First, the "219" figure is an estimate. That estimate is for sub adults ONLY. But more important, that estimate is based on the presumption that ALL great whites in the test area follow the annual migration that the researchers referenced. THEY DON'T. Many do, but NOT all. The point I'm making is, there are definitely MORE than 219 sub adult great white sharks in the Central California region of the sample test zone. There will never be a way to know exactly how many, but to say conclusively that they have a number, based on assumptions as ludicrous as "ALL white sharks follow an annual migration pattern" will not give their study credibility.
   comment# 1   - Kevin · Thousand Oaks, California · Mar 9, 2011 @ 9:57am

-- The figure of 200-300 hundred adults has been conventional wisdom among Californa Field Researchers since the late 1990s. Pete Pyle, Scot Anderson at Farallones as well as our team at Ao Nuevo Island, I had no idea that Chris Lowe worked with adult white sharks in the wild.. or what his experiences are... Meanwhile we havent seen anymore or fewer sharks since 1990, some seasons are better than others but its the same cast of sharks we've been seeing for decades. At the end of the vid clip below one can here the estimate for Eastern Pacific white sharks, its from a documentary that aired in 2003. This isnt news or a new theory. Interesting stuff: ------------------------------------------------------------------------------------------ Editor's Opinion (UCSC Santa Cruz Sentinel): February 23, 2004 Hits and Misses: THUMBS DOWN To the marine researchers at UC Santa Cruz for not acknowledging earlier the contributions from the Santa Cruz-based Pelagic Shark Research Foundation in conducting a study involving tagged sharks. A lawsuit was filed after an article appeared in 2002 in the journal Nature not giving any credit to work done by the Pelagic group. The matter was settled out of court with a UCSC scientist belatedly acknowledging the involvement of the PSRF." Cheers, Sean S.R. Van Sommeran Executive Director Pelagic Shark Research Foundation
   comment# 2   - Sean R. Van Sommeran · Santa Cruz California · Mar 9, 2011 @ 12:50pm

I call BS. I grew up in San Diego and white shark sightings were were common from Mexico all the way to Oregon and the same sharks swim up and down the coast. White sharks are far from endangered. I think they should stay protected but attacks on humans are going up world-wide and it is because the white shark breeding population is very healthy. Fisherman have always said that there are big white sharks off the coast of San Diego and the attack at Solona Beach a few years ago proves it. Shoot, one of the best places to see great whites in the whole world is at Guadalupe Island which is only a couple hundred miles off San Diego.
   comment# 3   - Josh · Denver, Co · Mar 23, 2011 @ 10:33pm
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