First census finds surprisingly few white sharks off California

Mar 09, 2011

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 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 have been found to congregate – and then they return to the coastal areas.

Explore further: Livingstone beetle specimens found after 150 years

Provided by University of California - Davis

3 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

Unveiling the underwater ways of the white shark

Feb 18, 2008

It's hard to study a creature when you only catch fleeting glimpses of it. Up until recently, that was one of the big stumbling blocks for marine biologists and ecologists, but advances in electronic tracking technology have ...

Great white sharks tagged for first time off Mass.

Sep 06, 2009

(AP) -- Massachusetts officials are using high-tech tags to track the movements of two great white sharks near Cape Cod - the first time the fearsome fish have ever been tagged in the Atlantic Ocean.

3 more great white sharks tagged off Mass. coast

Sep 08, 2009

(AP) -- A total of five great white sharks have now been electronically tagged off Cape Cod, allowing experts to track their movements and learn more about their migratory habits.

Plan for fingerprinting Great White Sharks

Aug 13, 2010

Computer scientists from the University of Bristol are collaborating with shark researchers to build an international visual biometrics database of Great White Sharks.

Recommended for you

Research helps steer mites from bees

Sep 19, 2014

A Simon Fraser University chemistry professor has found a way to sway mites from their damaging effects on bees that care and feed the all-important queen bee.

Bird brains more precise than humans'

Sep 19, 2014

(Phys.org) —Birds have been found to display superior judgement of their body width compared to humans, in research to help design autonomous aircraft navigation systems.

User comments : 0