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El Niño. This warming trend in the Pacific Ocean is on the tips of everyone’s tongue when wishfully discussing the possibility of enough rain this winter to quench our state’s historic drought. And it’s suspected to be the main culprit for some unusual behavior in the natural environment.
In recent weeks, observers have noted migrating whales coming closer to California’s shoreline, pelagic red crabs arriving in droves near Channel Islands National Park, and a spike in great white shark sightings off the coast of our Golden Gate National Parks.
But the perceived correlation between El Niño and the increase in recent shark sightings in and around the Golden Gate Strait hasn’t convinced Dr. John McCosker, emeritus chair of the Department of Aquatic Biology at California Academy of Sciences.
“The things we know are that the water temperature has changed significantly [approximately five degrees above normal],” explains McCosker, who is also a member of our Parks Conservancy Board of Trustees. “And that has affected the behavior of many animals in the ocean and on land, and that’s definitely involved with the appearance of white sharks. Whether it is a direct link—or a result of a cascade of events—has not been demonstrated.”
This time of the year (August through October), coincidentally, is when the waters from Monterey Bay to Tomales Bay in Marin County--and most notably around the Farallon Islands—become a feeding magnet for mature white sharks, due most likely to the abundance of California sea lions, harbor seals, and northern elephant seals.
So far, the population of white sharks spotted around the Farallon Islands and Point Reyes National Seashore isn’t out of the norm, but McCosker does acknowledge that some peculiar events have transpired this season.
Feeding off The Rock
Visitors to Alcatraz Island last month witnessed the first-ever recorded feeding behavior of a white shark on a seal or sea lion in San Francisco Bay—just a few feet from the dock (and a crowd of shocked onlookers).
Sharks swimming underneath the Golden Gate Bridge into the Bay is nothing new to scientists like McCosker. Thanks to ultrasonic tagging by scientists at the Hopkins Marine Laboratory, this behavior is well-documented.
But, according to Dr. Sarah Allen, an ecologist for the National Park Service, the unusual aspect of this feeding event was its location (inside the Bay) and its proximity to land. She has monitored pinniped (seal and sea lion) populations at Point Reyes and elsewhere in central California, and has never personally seen an attack so close, though others who study and tag sharks have.
McCosker reaffirmed that the feeding was unique, and the first attack of any kind reported in the San Francisco Bay in almost 90 years.
“There was a record in 1926 of a man and his dog being attacked by a shark—probably a white shark—at Bay Farm Island, now called Alameda,” he says.
A Great White “Party”
Another unique occurrence was a recent gathering of approximately 20 white sharks off the coast of Ocean Beach and Pacifica. This unusual “party” was spotted from a U.S. Coast Guard helicopter on October 16.
“The cluster was a social gathering, possibly related to feeding,” McCosker hypothesizes. “But no one can confirm—and is willing to make a statement—that this is why they are all here.”
“One could witness that sort of gathering at the Farallon Islands—particularly, August through October. But to see that off the coast there was unusual that we haven’t previously seen it anywhere near that abundance previously [so close to shore].”
Another Average Year
Nevertheless, these unusual phenomena shouldn’t alarm casual beach goers and park visitors. On average, according to McCosker, there are two or more encounters between white sharks and humans every year off the coast of Northern California, and one fatality approximately every decade.
And Allen and McCosker both say that 2015 has not been an outlier year of white shark sightings or encounters, at least for the waters off and around the San Francisco Bay.
“[The sightings are up] from Monterey to Half Moon Bay to Pacifica,” Allen reports.
But, according to scientists studying sharks, the numbers farther north--around the Farallon Islands and Tomales Bay--are on par with other years’ figures so far this year.
“Based on the study of white sharks off Tomales Point by scientists from the Tagging of Pelagic Predators Program, they have seen in a given year, about four [sharks] per day and about 70 individuals per year,” she explains.
Allen does note that, historically, El Niño years appeared to yield more shark attacks on pinnipeds (seals or sea lions), as noted in 1998.
“In the past El Niño events, there have been more sightings of white sharks and examples of shark bites on seals during El Niño years,” she says. “That has not, at least that I know, been documented [this year].”
Mysterious and Not-So Fearsome Fish
Despite years of observations, however, these sharks are still, in large part, a mystery to scientists. No one is quite sure where the pregnant great whites give birth. And researchers are finding that there are more great whites off the shores of Alaska, British Columbia, and even Hawaii (to name a few) than previously thought.
What is known is that white sharks often cruise at depths of 10 feet to 60 feet, and prefer a rocky terrain, and often hunt near seal colonies where, McCosker says, they are attracted to the “smell of feces.”
The sharks are also visual predators, and will sometimes “taste” surfboards and kayaks if they suspect they’re pinnipeds, which is the cause of most encounters. They typically vacate the scene after realizing their mistake. The shorter the surfboard or kayak, the more likely someone might be confused for a seal or sea lion, McCosker notes.
And maybe it’s this mysterious behavior and perceived fearsome nature that fuels much of pop culture’s fascination with the animal. While McCosker and Allen can’t say with certainty that the shark population off the shores of Golden Gate National Parks has increased significantly due to the projected El Niño, they will note that more people are on the hunt to document their presence, which in turn, means sightings are likely to rise.
Do you have questions about white sharks, or did you spot one off the coast of the Golden Gate National Parks? Contact the National Park Service at (415) 561-4700.