While swimming with sharks might seem like an aggressive form of leisure for the faint of heart, the naturalists at Birch Aquarium want you to know that floating above pregnant female leopard sharks resting along the ocean floor is about as safe as you can get.

From June to December every year, thousands of these docile creatures migrate to the warm waters of La Jolla Shores Beach to speed up their gestation process. While the number of sharks this year has not yet been recorded, Birch Aquarium Education Specialist Delanie Medina said it’s already more than previous years.??

“We had an El Nino in 2015, so that changes the water temperature here,” she said. “We actually didn’t see as many [sharks] aggregating on our coastline. Some scientists believe that could have been because all the water was warmer than usual, so that spot in front of The Marine Room wasn’t really a hot spot for them.??

“But this year, we’ve actually seen it bounce back to a more normal aggregation year where we do see them concentrated there.”??

It’s long been a mystery as to when the sharks started visiting La Jolla Shores Beach in the summer, and it wasn’t until 2013 that anyone knew why. Scripps Institution of Oceanography’s Andy Nosal researched the migration and determined that 97% of the sharks that visited were pregnant females drawn to the warm, calm waters of the area.??

“He was able to discover it by tracking them acoustically,” Medina said. “He would put transmitters along the coastline and attach acoustic tags to the leopard sharks through a fish-and-release sort of method.”??

Once scientists realized the population was mostly pregnant females, swimming above them became a lot less scary and a lot more magical.??

“Of course when we think of sharks, we think of the larger apex predators who are at the top of their food chain, like a great white,” Medina sad. “But [leopard sharks] are what we call benthic sharks, so they’re bottom-feeders.”??

Bottom-feeders who aren’t looking for human flesh, but rather benthic invertebrates like crabs, shrimp, worms and pretty much anything else that can be found on the ocean floor.??While leopard sharks can grow up to 7 feet long, the ones that come to La Jolla are typically 5 to 6 feet in length, according to Medina.

Small, calm, worm-eating, pregnant female sharks are not the things horror movies are made of, which is why snorkel tours during leopard shark season have become so popular at Birch Aquarium.?

“What we tell kids is that the sharks that come to this spot are pregnant animals. So if you think of any type of pregnant animal, you know they’re looking to rest during the daytime. And we’re not anywhere on their list of prey.”??

Birch Aquarium’s Shark Snorkels take place from 8 a.m. to 10 a.m. every Saturday and Sunday from July through September. Participants must be at least 10 years old, have intermediate swimming ability and supply their own gear. Previous snorkeling experience is recommended and a pre-purchased reservation is required. Cost is $25 for Birch Aquarium members and $30 for nonmembers.

For more information and to reserve your spot, visit aquarium.ucsd.edu.