First California White Shark Census Yields a Surprise
Biologists expected to find more white sharks
Roger Di Silvestro
Biologists at the University of California-Davis (UC-Davis) and Stanford University recently conducted the first rigorous scientific estimate of white shark numbers
in the northeast Pacific Ocean
and found that there are far fewer white sharks off central California than shark experts had expected. The study, published in the journal Biology Letters
, also is the best estimate ever made among the world's three known white-shark populations (the others are in Australia/New Zealand and South Africa).
Sailing in small boats across sites where white sharks congregate, the researchers lured the predators into photo range using a seal-shaped decoy on a fishing line. From 321 photographs of the uniquely jagged edges of shark dorsal fins, the biologists identified 131 individual sharks, allowing them to estimate that 219 adult and sub-adult white sharks
cruise the region.
How Old Is That Shark?
White sharks are classed as sub-adults when they reach 8 to 9 feet in length and they from eating fish to mostly marine mammals. They become 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," says 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 leading expert on sharks, tuna and billfish. "It is this fact that makes it possible to estimate their numbers. Our goal is to keep track of our ocean predators."
What’s in a Name?
The great white shark apparently isn’t all that great, according to shark expert Scot Anderson. “It should be ‘white shark,’” he says. “There is no ‘great white.’ But most people do not know this, so the ‘great’ seems to be stuck these days.”
Satellite tagging studies have demonstrated that white sharks in the northeast Pacific make annual migrations from coastal areas off 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 congregate before returning to the coastal areas.