Why is California's Great White shark population rising? 'Red triangle' sees 30% more predators in 10 years

"The finding, a result of eight years of photographing and identifying individual sharks in the group, is an important indicator of the overall health of the marine environment in which the sharks live," Oregon State University researcher and study co-author Taylor Chapple said in a statement.

Why is California's Great White shark population rising?

A variety of factors may be contributing to the rise in the population of the predator, which can grow up to 20 feet long and live to be 70 years old. The Marine Mammal Protection Act of 1972, as well as a reduction in gillnets off the coast of California, are assisting in the recovery, according to Chapple.

According to Mercury News, there were 219 adult and sub-adult great whites (with a range of 130 to 275) in the region, according to a 2011 survey. Sub-adult sharks aren't completely mature yet, but they're large enough to eat dolphins, sea lions and other sea mammals. Great white sharks are incredible hunters, with hundreds of sharp, triangular teeth and the ability to swim at 35 mph. Many people knew about great white sharks from films like 'Jaws', which sensationalized their threat to humans.

Good news for the whole ecosystem

One of the reasons for the rise in the shark population could be the Marine Mammal Protection Act, which was signed into law by former president Richard M Nixon in 1972. This put an end to the killing of whales, sea lions, elephant seals and other shark-eating species, causing their numbers to skyrocket.

The area off the coast of California is referred to as the 'red triangle' because it is shaped like a triangle. Salvador Jorgensen, a senior research scientist at Monterey Bay Aquarium, told KQED in 2018 that the name comes from the amount of seal blood in the water. However, white sharks can often be found outside the 'red triangle' and can be spotted all along the coast.

The rise in shark numbers, according to Chapple, is a positive sign for the whole ecosystem. "The health of our coastal marine ecosystem depends on robust populations of large predators," he said. "So our findings are not only good news for white sharks, but also for the rich waters just off our shores here."

Shark fins are like fingerprints

From 2011 to 2019, the researchers spent over 2,500 hours studying the three sites and taking images from above and below the water during various times. They were also able to use a seal decoy to attract the sharks to the research boat, where they took over 1,500 photos to better classify the sharks, thanks to their dorsal fins.

"Every white shark has a unique dorsal fin. It's like a fingerprint or a bar code. It's very distinct," Chapple said. "We were able to identify every individual over that eight-year period. With that information, we were able to estimate the population as a whole and establish a trend over time."

No more gillnet fishing

Sharks are mostly hunted for their fins. The majority of sharks are killed by industrial fishing and the fin trade, according to Francesco Ferretti, a marine ecologist at Hopkins Marine Station of Stanford University. “They are dying on the high seas, and many are targeted for their fins,” Ferretti told KQED, adding that sometimes a shark’s death is unintentional. “Blue sharks, silky sharks, hammerheads and thresher sharks, those are the species that can be caught as bycatch in large quantities.”

“As apex predators, they help stabilize entire ecosystems. When sharks are thinned out at the top, animals further down the food chain can become overhunted,” he added. In 1994, California lawmakers passed legislation prohibiting the killing of white sharks in state waters out to three miles, which could be another reason for the rise in shark population. Finally, in 1990, California voters approved Proposition 132, which prohibited gillnet fishing in state waters, which can often kill sharks, dolphins, turtles and other marine life accidentally during commercial fishing.

Fewer females are cause for worry

The fact that 60 per cent of the sharks off the coast of Northern California were males and 40 per cent were females raises other questions, Mercury News reported. The researchers are worried about the area's low adult female population, which is estimated to be about 60. "That underscores the need for continued monitoring of white sharks, as there are relatively few reproductively active females supplying the population with additional sharks," the study's lead author, Montana State University marine ecologist Paul Kanive said. "Losing just a few animals can be really critical to the larger population," he continued. "It's important that we continue to protect them and their surroundings."