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First census finds surprisingly few white sharks off California

March 8, 2011

Counting sharks

This video includes clips from the new photo-census study and also from earlier studies that put satellite-tracking tags on white sharks to find out where they go.

Video (49 sec)

Videography by courtesy of Taylor Chapple

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 Café,” 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.

About UC Davis

UC Davis is a global community of individuals united to better humanity and our natural world while seeking solutions to some of our most pressing challenges. Located near the California state capital, UC Davis has more than 34,000 students, and the full-time equivalent of 4,100 faculty and other academics and 17,400 staff. The campus has an annual research budget of over $750 million, a comprehensive health system and about two dozen specialized research centers. The university offers interdisciplinary graduate study and 99 undergraduate majors in four colleges and six professional schools.

Media contact(s):

  • Taylor Chapple, Wildlife, Fish and Conservation Biology, tkchapple@ucdavis.edu (Taylor Chapple is traveling through March. Contact Sylvia Wright for his telephone number.)
  • Randy Kochevar, Stanford University, (831) 655-6225, kochevar@stanford.edu
  • Kat Kerlin, UC Davis News Service, (530) 752-7704, kekerlin@ucdavis.edu

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