In California, great white sharks suddenly seem to be everywhere.
Unnerving congregations of them have appeared near popular beaches from San Diego to Santa Cruz. Recreational fishermen have caught many of the protected fish from piers in southern California, and commercial fishermen reported a dramatic uptick in young great whites caught in their nets starting in 2004. Juvenile great whites seem to be swimming farther north than they have in the past, scientists say. At the Channel Islands, resident researchers are astonished at the escalating numbers of sea lions staggering ashore with the gruesome telltale wounds of shark attacks, while sea otter carcasses mangled by shark bites are washing up on the mainland at seemingly unprecedented rates. Thankfully, the risk of attack on humans remains miniscule, and the occasional incident tends to receive more attention than it probably deserves. Earlier this month, for instance, authorities temporarily banned water activities at Santa Cruz beaches as TV stations and newspapers made a top story of a great white that nipped a local man’s sea kayak.
Amid the media hype over sharks and a wealth of inconclusive data, West Coast biologists can’t seem to agree whether or not great white numbers are increasing. Scot Anderson, a shark biologist with the Tagging of Pelagic Predators, or TOPP, program, doesn’t think California’s great white population is growing – at least not significantly.
“We just don’t see evidence of that in our tracking data and in our number of re-sightings [of individual sharks],” says Anderson, who tags and studies great whites mostly around the Farallon Islands and in the vicinity of Tomales Point, on Marin County’s Point Reyes peninsula.
Anderson says he has talked to Coast Guard pilots who patrol California’s shoreline via aircraft. These aerial surveys are an effective tool for spotting and counting sharks – but according to Anderson, the Coast Guard officials have not seen a change in abundance.
“They’ve been seeing them forever,” he says.
So, what’s going on?
“The main thing causing this excitement about great whites is that there are more people doing all kinds of things on the water,” Anderson says.
Sean Van Sommeran, a Santa Cruz conservationist, believes there has been no appreciable population increase and, even, suggests it is reckless to assume the animals are no longer threatened by illegal capture and harassment. He believes media hype, more people in the water, more attentive scientists interested in sharks, and water temperature-related shifts in shark migration patterns have created an illusion that the animals’ numbers are growing.
In 2012, several environmental organizations were even concerned enough to petition the state to list great whites as endangered. The petition was rejected in 2014 as Department of Fish and Wildlife biologists determined the species – Carcharadon carcarius – to be healthy.
But the population estimates remain all over the board, from as few as 339 along the West Coast to more than 3,000.
But the population estimates remain all over the board, from as few as 339 along the West Coast to more than 3,000. Van Sommeran, who founded the Pelagic Shark Research Foundation in 1990 and says he has since tagged and tracked 164 great whites, says that documenting a population increase amid such fuzzy numbers is impossible, since not only are current numbers unclear but nobody knows how many great whites there were in the past.
“There is not a shred of empirical evidence or data showing that their numbers are going up,” Van Sommeran says.
But other scientists have interpreted data and anecdotal information very differently. Chris Lowe, director of the “Shark Lab” at the California State University at Long Beach, is convinced great whites’ numbers are escalating – and rapidly so – in Mexico and California. Expanded marine reserves and more closely regulated fisheries have reduced mortality of young sharks in gillnets, he says, while 1972’s Clean Water Act has improved conditions in the coastal areas where the sharks live. Lowe coauthored a 2013 paper in the journal Fisheries Research in which he and his colleagues concluded that great whites in California are seeing more successful reproduction and, in turn, a population increase.
But more than any other factor, Lowe credits California’s growing pinniped population for what he theorizes is a great white comeback.
Men killing fur seals on St Paul Island, Alaska, 1890s
“The decline in marine mammal numbers in the late 19th century and early 20th century probably caused a population decline in great whites,” Lowe says. Now that seals and sea lions are bouncing back, he says, sharks are too.
After being hunted nearly to extinction a century ago, the number of California sea lions has exploded from just several thousand in the 1940s to near-vermin levels of between 300,000 and 400,000 today. The animals are so abundant that they are quite literally spilling inland into the waterways of the Central Valley. Numbers of harbor seals have similarly increased, and the northern elephant seal has staged a comeback, too. These species are the favored prey items of great whites, and, intuitively, it makes sense that shark numbers would respond to a boom in pinniped abundance.
Except, why now, after marine mammals have been proliferating for decades?
“If the population of marine mammals was a controlling factor on shark numbers, we would have seen a rise a long time ago,” Van Sommeran says.
He also believes the data showing an increased rate of attacks on marine mammals is a result of “observer bias.”
“If you look for sharks attacking sea otters, you’ll find them,” he says.
He is referring to a study published in 2015 in the journal Marine Mammal Science in which described “a striking increase in the frequency of white shark bites on sea otters” since 2003. The authors, who estimated that shark attacks now account for more than half of all California sea otter deaths, refuted the notion of observer bias within their published findings. They attributed the trend to more great whites off the West Coast, changes in the places that sharks hunt, or both factors.
On the Channel Islands, resident scientist Jeff Harris and his colleagues have seen a sharp uptick in California sea lions hauling onto shore bearing shark bite wounds – some from mako sharks, he says, but mostly great whites.
“Prior to 2010, there were so few shark bites that we didn’t even notice them,” says Harris, a National Marine Fisheries Service research ecologist who has been studying pinnipeds at the islands for a decade.
Then, beginning about eight years ago, wounded pinnipeds began appearing in startling numbers. Last year, Harris says, scientists stationed on San Miguel Island counted nearly 500 seals and sea lions with enormous gashes and missing limbs.
“And we’re just seeing the survivors,” says Harris, who estimates a 50-percent death rate for sea lions following white shark attacks.
Asked if he and his colleagues are just seeing shark bites now that they know to spot them, Harris says no way.
“These are huge wounds,” he says. “Some of the animals are practically ripped in half. There’s no way we were just missing them.”
It seems obvious sharks have changed their hunting habits, then – but the experts debate whether this is a result of more sharks along California’s coast, or just a change in their activity patterns. Lowe suspects both: He believes an increase in great white numbers at preferred hunting areas in northern California has caused adult sharks to disperse and go looking for new territory in which to hunt seals and sea lions – thus, the spike in attacks at the Channel Islands.
“Año Nuevo and the Farallones have become too crowded,” Lowe says. “The bigger sharks wind up crowding out the smaller sharks.”
At Mexico’s Guadalupe Islands, another hotspot of white shark activity, researcher Mauricio Hoyos Padilla first saw a juvenile great white in 2007, four years after he began tagging and studying sharks here. Today, he says, 5-to-7-foot great whites are a normal occurrence at the islands, which are more than 100 miles from the mainland. He suspects the great white population is growing, though he notes such a conclusion could be premature.
“We’ve seen more sharks, but we’re also looking harder for them,” says Hoyos Padilla, who is the general director of the organization Pelagios-Kakunjá A.C.
While scientists don’t all agree that shark numbers are certainly rising, there is something closer to a consensus on a different observation – that juvenile great whites less than seven or eight feet long are now frequenting northern California waters that they rarely visited before.
In June of 2014, Van Sommeran says he personally saw one of the first juvenile great whites documented in Monterey Harbor. That summer, and in the three summers since – including 2017 – five- and six-foot-long great whites have been spotted numerous times in Monterey Bay and as far north as Pacifica. Van Sommeran suspects there has been a range shift. Specifically, Van Sommeran believes there are now fewer great whites at the southern extent of their range in southern Baja California and more at the northern end.
Slightly different is Lowe’s interpretation – that more young sharks appearing in northern California is the result not of a range shift but a range expansion. That is, Lowe says the sharks are still using their historical nursery grounds in Mexican waters but are also making use of habitat farther north.
But both scientists believe the novel occurrence of many young great whites in northern California is related to shifting ocean currents and an increase in average surface water temperatures along the California coast.
“But once we go into a La Niña cycle and the cold water returns, we might see these small sharks retreat south,” Lowe says.
Scientists will probably never have the tools to nail down a precise shark count the way biologists are able to do in censusing of large terrestrial animals. But there is at least one fact that can hardly be debated: While observed attacks on sea otters and sea lions rise, the rate of attacks on humans has not dramatically changed over 60 years. In absolute numbers, California shark attacks are up, from .9 attacks per year in the 1950s to 1.4 annually in the first years of this decade, according to data collected by Francesco Ferretti, a researcher at Stanford University’s Hopkins Marine Station. However, this increase has been eclipsed by the blitzkrieg of people rushing into the ocean, and in a paper published in the journal Frontiers in Ecology and the Environment, Ferretti calculated that any given Californian was more than 91 percent less likely to be attacked by a shark in 2013 than in 1950.
The tiny risk of being attacked by a great white doesn’t tell scientists very much about shark numbers, but it’s a fascinating observation to Anderson.
“The really interesting thing is that sharks aren’t eating people all the time,” Anderson says. “In a lot of these situations where they see a bunch of sharks, there are people in the water nearby, and the sharks just don’t seem to care.”