Though usually spotted in summer months, leopard sharks were reported off La Jolla Shores’ shallower waters in early March, leading some to speculate about their premature arrival.
“For Andrew Nosal, associate professor of biology at Point Loma Nazarene University and an expert on leopard sharks in La Jolla, their late-winter residency is ‘not that unusual.'”
The summer is when we see leopard sharks, thought to use La Jolla’s warmer summer water to incubate their new pregnancies, “in greatest numbers and most consistently day to day,” Nosal said.
However, Nosal’s study of leopard sharks from 2009-2012 indicated some are present year-round.
Though leopard shark numbers start increasing in late June, peak in August and September and then dwindle by December, Nosal said some show up in the winter for a few weeks at a time before disappearing again.
“It would not surprise me if the [current] leopard sharks disappear again for a period of time, and then … show up again later this spring,” he said.
Where do leopard sharks go when they leave La Jolla?
“We found that when the leopard sharks mostly left in the winter, about half of them went north,” Nosal said, with acoustic receivers detecting them as far north as Los Angeles, where they again disappeared.
Those sharks may have continued their swim north or might have gone farther offshore, he said, returning south along the coast closer to summer.
The other half of the sharks “seemed to disappear from La Jolla” with the others, Nosal said, but were never detected anywhere else and simply reappeared in La Jolla the next summer.
These mysteriously-reappearing sharks are those that would periodically show up during the winter for a couple of weeks at a time, he said. “I suspect those are the sharks that we’re seeing right now.”
Maybe those sharks divert themselves to slightly deeper water where they can’t be detected but “stay in the general neighborhood,” Nosal said.
Wherever the sharks swim off to, he said we will still see “the full aggregation showing up in the summer as usual.”
Why return in winter?
It’s not known why some of the leopard sharks make a winter appearance, Nosal said.
These winter arrivals may be at the end stages of their 10- to 11-month gestation period, he said, noting the summer sharks are all female and at the beginning of their pregnancies.
“Maybe they’re getting ready to give birth,” Nosal said. “It would be pretty interesting to see if we started seeing more little leopard shark pups showing up in La Jolla in the next month.”
A fin place to live
Emphasizing that leopard sharks are “completely harmless” to humans,” Nosal said “we should be excited to have these sharks in our backyard. They’re definitely an emblem of La Jolla.”
The sharks’ abundance indicates the local ecosystem is healthy, he said, as “these large predators would be the first ones to go because there would not be enough food for them.”
“There’s no such thing as shark-infested waters,” Nosal added. “This is their home and you can’t infest your own home.”
