Great White Shark Numbers Rise Off Northern California Coast
You’re still far more likely to see them in movies or TV shows than in person, but numbers of great white sharks appear to be increasing along California’s northern coast, say scientists who have spent years in follow hundreds of toothy predators by their distinctiveness. fins.
The comprehensive new study concluded that nearly 300 adult and sub-adult white sharks live between Monterey Bay, the Farallon Islands and Bodega Bay, an area sometimes referred to as “the red triangle.” Subadult sharks are not fully mature but still large enough to eat seals, sea lions and other marine mammals.
That’s a modest increase from 10 years ago, the researchers said, and a clear indication that ocean conditions in the region are generally moving in the right direction.
“A healthy population of white sharks means there are healthy populations of sea lions and elephant seals that they eat,” said Paul Kanive, marine ecologist at Montana State University and lead author of the study. . “And that means lower levels of the food chain, like fish, are healthy enough to support marine mammals.”
With hundreds of sharp, triangular teeth and the ability to swim at 35 mph, great whites are incredible hunters. They can grow up to 20 feet long and weigh over 4,000 pounds. For generations they have been mysterious and often dreaded. Scientists knew little about how many, where they swam, or their mating habits. Most people discovered the great whites through films like “Jaws”, which made their threat to humans sensational.
But in recent years, researchers at Stanford University and the Monterey Bay Aquarium, two institutions that funded the latest research, have placed electronic beacons on sharks to track their movements. They worked with scientists from other research centers to photograph individual sharks and compile databases of their numbers – a family album of marine apex predators.
For the latest study, marine biologists worked on boats from 2011 to 2018 off the southeastern island of Farallon, located 26 miles west of San Francisco, from Año Nuevo Island along the coast of San Mateo County and Tomales Point in Marin County.
For 2,587 hours, scientists collected photographs both above and underwater. To attract white sharks to their boat, they put a small amount of seal meat in the water to create a scent. Then they brought the sharks together with a seal decoy made of black carpet and tied to the boat with a fishing line.
Scientists have captured more than 1,500 photographs, focusing on the jagged edge of the sharks’ famous upper fin.
“Each white shark has a unique dorsal fin. It’s like a fingerprint or a barcode, ”said Taylor Chapple, assistant professor of fishing and wildlife at Oregon State University, and co-author of the study. “It’s very distinct.”
In a similar study published in 2011, researchers estimated that there were 219 adult and sub-adult great white sharks in the same area off Northern California, with a possible population of 130 to 275. But the latest study estimates that as of 2018, there were 266 white sharks, with a possible range of 218 and 313.
There are probably three reasons for the increase in numbers, experts say. First, President Nixon signed the Marine Mammal Protection Act in 1972. This ended the hunt for seals, sea lions, elephant seals, and other animals that sharks eat, resulting in skyrocket their numbers.
Second, in 1994 California lawmakers banned the slaughter of white sharks in state waters up to three miles away. Finally, Californian voters ended gillnet fishing in state waters when they passed Proposition 132 in 1990. Gillnets are large nets that can often trap and accidentally kill sharks, fish and fish. dolphins, turtles and other marine life during commercial fishing.
But white sharks still face threats. They live along the northern California coast from September to February, then swim 1,500 miles each way to an area between Hawaii and Mexico called “the Shark Cafe,” where they congregate, eat, and mate. In the open sea, they risk being killed by longlines and other deep-sea fishing practices.
The new study found that 60% of sharks off northern California were males and 40% females, raising further concerns.
“Losing a few animals can be really critical for the wider population,” said Kanive, who set up a GoFundMe account to help fund research after other funding failed. “It is important that we continue to protect them and their environment.”
Do more sharks mean more people are at risk of attack? Probably not, experts say.
In a tragic interaction last May, surfer Ben Kelly, 26, of Santa Cruz, was bitten 100 meters from Manresa State Beach in Aptos. The bite occurred behind his right knee, hit an artery, and he bled to death. An investigation by state wildlife biologists found the shark to be at least 10 feet long, larger than juveniles which increasingly congregated in the area as the waters warmed.
But the risk of being injured or killed by a great white shark off the coast of California is generally minimal. A study published by scientists at Stanford in 2015 found a 1 in 17 million risk of a surfer being attacked by a white shark off the coast of California. The risk fell 91% from 1950 to 2013, scientists found, as the number of attacks remained essentially constant, but the human population of the California coast tripled from 7 million in the 1950s to 21 million. in 2013.
“The likelihood of people encountering a white shark is very low,” Kanive said. “It’s a very rare event.”