Study: Great White Shark Numbers Increasing Along the Northern California Coast

Study: Great White Shark Numbers Increasing Along the Northern California Coast Study: Great White Shark Numbers Increasing Along the Northern California Coast Warning signs for shark sightings. (Frederic J. Brown/AFP via Getty Images)

By Jim Thomas | Monday, 24 May 2021 06:37 PM

The number of great white sharks appear to be increasing along the Northern California coast, say scientists who tracked hundreds of the apex predators by their distinctive fins, reported the Daily Mail.

The exhaustive new study, published in “Biological Conservation,” concluded there are nearly 300 adult and sub-adult white sharks living between Monterey Bay, the Farallon Islands and Bodega Bay, an area sometimes called “the red triangle.”

The area earned that sobriquet because of the amount of seal blood in the water, Salvador Jorgensen, a senior research scientist at Monterey Bay Aquarium, told KQED in 2018.

“A healthy population of white sharks means there are healthy populations of the sea lions and elephant seals they eat,” said Paul Kanive, a marine ecologist with Montana State University and lead author of the study. “And that means that the lower levels on the food chain, like fish, are healthy enough to support the marine mammals.”

Sub-adult sharks, which can grow up to 20 feet in length and reach 70 years in age, are not fully mature but still big enough to eat seals, sea lions and other marine mammals.

That is a modest increase from 10 years ago, researchers say, and a clear indication that ocean conditions in the area are generally trending in the right direction.

“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,” said Oregon State University researcher and study co-author Taylor Chapple in a statement.

The Marine Mammal Protection Act of 1972, as well as the reduction in gillnets on the California coast are aiding the rebound, Chapple explained.

“Robust populations of large predators are critical to the health of our coastal marine ecosystem, he added, so our findings are not only good news for white sharks, but also for the rich waters just off our shores.”

It was estimated there were 219 adult and sub-adult great whites (with a range between 130 and 275) in the area, the Mercury News reported, citing a 2011 study.

The researchers spent more than 2,500 hours observing the three sites, while collecting photographs between 2011 and 2019 from above the water and below the water during period periods.

They were also able to lure the sharks to the research boat with a seal decoy, taking more than 1,500 photographs to properly identify 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.”

However, the researchers are concerned about the low number of adult females in the area, believed to be around 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 added.

“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.”

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 are believed to mate. While in the open ocean, they are at risk of being killed by long-lines and other high seas fishing practices, reports NPR.