Why a Rise in Great White Sharks Off the California Coast is Good News

The population of great white sharks off the coast of central California is increasing, according to a study, which means populations of other animals like seals and fish may also be healthy.

Between 2011 and 2018, and over the course of more than 2,500 hours, a team of researchers identified nearly 300 adult and sub-adult individual great white sharks at Farallon Island, Año Nuevo Island, and Tomales Point—three sites where the apex predators are known to gather.

A similar study conducted in 2011 found 219 great whites, which suggests that numbers are slowly increasing in the area.

Paul Kanive, a marine ecologist at Montana State University and lead author of the study, which was published in the journal Biological Conservation, told The Mercury News: "A healthy population of white sharks means there are healthy populations of the sea lions and elephant seals they eat.

"And that means that the lower levels on the food chain, like fish, are healthy enough to support the marine mammals."

Great white sharks and other top marine predators have a varied diet, which means they don't tend to hunt any specific prey to exhaustion, thereby allowing the various species to recover.

The study is the latest piece of research to reflect the importance of healthy shark populations. For instance, a 2008 report by ocean protection organization Oceana found that a decline in large shark populations along the eastern coast of the U.S. coincided with a spike in ray, skate and smaller shark populations, with the number of some species increasing tenfold.

The species whose numbers surged most markedly of all was the cownose ray, which proceeded to all but wipe out most of the scallops, oysters and clams in the area, resulting in the closure of a century-old scallop fishery.

Oceana said in the report: "As top predators, sharks help to manage healthy ocean ecosystems. And as the number of large sharks declines, the oceans will suffer unpredictable and devastating consequences."

In their study, Kanive and his team identified several factors that may have helped great white shark numbers to recover in the area.

In 1994, California passed a great white shark fishing ban and introduced tighter restrictions on gill nets, which can trap sharks, dolphins, turtles and other species. 1972's Marine Mammal Protection Act also led to the recovery of populations of seals, elephant seals and other marine mammals, which form the main bulk of a great white's diet.

The authors of the study said that the increase in great white numbers is slight enough to be described as "equivocal," and could also be explained by regional fluxes in density. However, they said they were "cautiously optimistic."

Kanive wrote in an update on a GoFundMe page set up to help fund the research: "The results reflect a small (<315) population of white sharks in this area.

"In addition, we investigated population trends for each demographic (sub-adult and adult males and females) and found evidence of a modest uptick in numbers of adult males and females over the study period.

"We are cautiously optimistic of a small but healthy population off central California."

great white shark, stock, getty
A stock image shows a great white shark jumping out of water. Shark populations off the coast of California have risen in recent years, according to a study. Getty Images