- Posted September 6, 2012 by
La Jolla, California
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LATE SUMMER ARRIVAL OF LEOPARD SHARKS THRILL BEACH-GOERS!
Officially, summer may be considered over, but tell that to all the people flocking to La Jolla Shores to enjoy the beautiful leopard sharks that frequent the area this time of year.
The La Jolla Light newspaper recently had a story about this phenomena. Andy Nosal, a Ph.D. candidate at Scripps Institution of Oceanography, "has dedicated his graduate career to studying this schooling. He wants to know why the harmless leopard sharks (Triakis semifasciata) keep returning to the same spot in La Jolla year after year, and what they do when they get here," noted the Light.
This past July 9, Nosal presented his research in a talk entitled, “Local Legends: the Leopard Sharks of La Jolla Shores" in a series hosted by UCSD's Birch Aquarium.
To his credit, Nosal emphasized the importance of the sharks. "They are not only extremely important for our local marine environment, but they are also very important for our local economy.” People flock each summer to see these sharks in the shallow waters just south of La Jolla Beach and Tennis Club. Shark Ttours do brisk business in the area and groups of kayakers and paddle-boarders descend onto the Boat Launch area to get a closer look. This is also the prime area for divers and snorkelers to gear up at and enter the water.
I paid a visit early this morning at high tide to the area immediately west of the Marine Room restaurant. A diver told me this is the best spot to really experience the wonder of swimming with the leopards.
After walking the short distance past the private confines of the La Jolla Beach & Tennis Club, I put my backpack up on a wall well away from the surf and jumped right in. Though the water is slowly chilling up again as we move into September, it was entirely swim-able.
Almost immediately, I found myself surrounded by about 5-6 medium sized sharks and they seemed to swim in a circular pattern around me. It was magical and I felt like I was dancing with them.
Soon enough, they were off but not longer after, more sharks moved along to take their place. I wished I had a good underwater camera, as the markings and patterns on the leopards were full of intricate detail. The best I could do was snap a few pictures showing dark shadows moving along under the crystalline water.
It turns out that almost all of the schooling leopards are pregnant females .Scripp's Nosal managed to employ acoustic telemetry or sound tracking, to follow the sharks. His research group managed to catch, tag and release more than 150 sharks along La Jolla Shores. Their daily habits were examined and the longer-range migrations of the sharks were studied.
“The most amazing thing we found, is if you look at individual sharks, there is remarkable synchrony,” Nosal said. While there is some individual variation, the sharks tend to school together, and depart as a group once the water cools or predatory sea lions arrive," The sharks delight in spending daylight hours in the warmest, shallowest waters of the surf zone. That would be the flat and protected area around the Marine Room restaurant. Upon night fall, the leopards head out to sea where they feed in nearby squid breeding grounds.
This particular area of La Jolla Shores is a protected Marine Sanctuary; it is an area free from the threat of fishing or poaching. The easy proximity to food offshore makes La Jolla Shores a prime spot for the sharks. “By coming back to the aggregation site every day, they’re in a good position to go forage as soon as the sun goes down,” Nosal was quoted as saying in the Light article.
These very mellow pregnant females may use the warm water along the popular beach to improve the success of the gestation of their young.
“What we think is going on is that these females are incubating … kind of like what a mother bird does,” he said. Nodal theorizes that the leopard sharks might spend time in warm waters for the same effect.
Though the sharks may be marine creatures, there is also a great similarity they have with their fellow female humans. “Where are the males?” Nosal asks. “We would think that the males would like all of these same things: nice, calm warm water in La Jolla, a lot of food, not to mention tons of females around.”
Yes, that does seem to be a big mystery. But the doctoral candidate has another theory here: he suspects that the females are actively avoiding the males’ excessive mating attempts. It's a girls only shark club va-cay and where ever the males are, these female leopards are making the most of their time in the lovely, languid, jewel-like coastal waters of La Jolla Shores.
photo credit: Nosal / Scripps courtesy of La Jolla Light.