Thursday, July 26, 2012
Scientists compare the waters off of California to Africa’s Serengeti Plain for its richness of life. Most of the Pacific Ocean’s top predators thrive there, including great white sharks, but San Diego’s offshore dorsal-finned residents are mostly harmless pups.
"We don’t actually see too many large Great White Sharks off of Southern California. They occasionally come through but we don’t have any resident fish, we think, in the area," said Nick Wegner, shark researcher with Scripps Institution of Oceanography.
San Diego waters provide a nursery ground for the 5-foot-long great white newborns, but their parents tend to stay away, said Wegner.
"There’s no parental care for white sharks, and so once the mom shark drops off the pups, she leaves and the pups are there to fend for themselves, and so the pups seem to end up off our coast in southern California and they’re probably attracted to high abundances of fish, generally calm waters and -- the area where they best feel they can survive," Wegner explained.
The question that remains is exactly where females go to give birth.
"We’ve never actually seen a white shark give birth, but because we have high numbers of juveniles in southern California we suspect that they give birth somewhere in southern California or in adjacent waters," said Wegner.
San Diego Lifeguard Lt. Greg Buchanan said “mom” does swim in close to shore on occasion to show off her large dorsal fin. Most recently on July 2 when a lifeguard and eight witnesses spotted what they believed to be a 12-15 foot great white lurking off of La Jolla Shores. Swimmers were called out of the water and the beach was closed.
"The water was super clear that day so we got a helicopter up within a few minutes, we had a rescue boat, jet skis, and all the lifeguards looking," said Buchanan.
Buchanan said the big one got away that day, but he said shark sightings are on the rise.
"Our criteria is that if we find the confirmed shark sighting within 500 yards of the shore, we’re going to basically consider a closure, and then the area outside the 500 yards is what we’ll describe as an advisory, which means we’re going to tell everybody what we’ve seen and let them know we’re under a shark advisory and then they can choose to exit the water or not."
Buchanan said the most common area for sightings is La Jolla, which is home to approximately 300 seals and sea lions -- a great white's favorite meal.
But Wegner said La Jolla’s marine mammal population pales in comparison to other California beaches. The National Marine Fisheries Service estimates there are more than 300,000 seals and sea lions along the California coast -- a number that has exploded in the last 40 years since the passing of the Marine Mammal Protection Act.
"Most of the large centers for large sharks are in larger areas where there’s abundance of seals and sea lions and elephant seals. And so that’s why we see an abundance of white sharks off the central coast," said Wegner.
The two main population centers for adult Great White Sharks is the Farallon Islands off of San Francisco and Mexico’s Guadalupe Island.
But La Jolla offers another draw for large sharks, according to Chris Lowe, the director of the Shark Lab at Cal State Long Beach.
"One of the interesting things about La Jolla is you have that deep water canyon there. So it’s possible that these sharks are staying deep, and might periodically come up the canyon where they’re exposed to shallow water."
Lowe said California’s white shark population is on the rise because commercial fisheries are more closely regulated and pups aren’t dying in the nets. "White sharks have been protected in California since 1994, and it has been since about that time that we've seen an increase in sightings."
Wegner said great whites aren’t the only large sharks off San Diego.
"Off the coast here we have a lot of Mako sharks and blue sharks. Those are probably two of the most common oceanic sharks, large sharks, off our coast," he said. "We also have thresher sharks, which come through and they drop off their pups in the spring and summer months and they can get quite large as well."
Wegner said the sharks off of San Diego are mostly harmless to swimmers.
"We’ve only had a couple fatal shark attacks in the last hundred years in San Diego County, so shark attacks are very rare in San Diego and there’s always a lot of excitement generated when a white shark is spotted, but there’s very few incidents with them attacking people," he said.
The Pacific coast had 108 shark attacks recorded in the 20th century. Between 2000 and 2010 there were 54 attacks. Most victims survived. The latest fatality happened in 2008 off Solana Beach in north San Diego County.
"I would always tell people that sharks exist in the ocean and so they need to know that and then basically be aware and if you see anything that you think is unusual that you think might be a great white shark they should tell a lifeguard immediately," said Buchanan.