Species of the Month: Unique horn shark makes a home in La Jolla waters

We’re all familiar with La Jolla’s sea lions, harbor seals, orcas, garibaldi and seabirds. But in this series of stories called Species of the Month, the Light sheds light on other, lesser-known marine creatures in local waters, their role in the ecosystem and more. 

There are a lot of things that make the horn shark unique — its mouth structure, its eggs, its eyebrows — yes, eyebrows.

The horn shark, found in shallow, rocky waters, is common in places such as La Jolla Shores and La Jolla Cove. It’s more active at night than during the day.

“They are a pretty interesting group of sharks,” said Ben Frable, a fish expert at the Scripps Institution of Oceanography in La Jolla. “They are not what you might picture when you think of a shark, and gets people away from the stereotype of what a shark looks like.” 

Reaching only about 4 feet long, horn sharks are smaller than other shark species and have tan or beige skin with spots to help with camouflage. Their name comes from the unique protrusions on their back that resemble horns and serve as a defense mechanism against predators including other sharks, elephant seals and some large fish.  

Frable chuckled as he recalled a ZooBooks commercial from the 1990s that featured a video of an angel shark biting down on one of those protrusions and immediately spitting out the horn shark. 

Horn sharks additionally “have these eyebrows and eyes on their head that allows them to have more range of view for predators, and they can even hide in the sand, so the eyes allow them to obscure their body while looking around,” Frable said.

“They also have a unique mouth and jaw structure because their jaws are modified to crush hard-shelled invertebrates like crabs or mollusks, and its mouth is on the bottom of its head instead of in front. So instead of having big ferocious teeth, the teeth are smaller and designed for crushing shells.” 

Horn sharks occasionally will enter tide pools to eat the creatures there. 

Though there has never been commercial fishing of horn sharks, remains have been found at Indigenous sites, suggesting that humans once ate them. 

Perhaps the most unique thing about the horn shark is its eggs, which regularly wash to shore.  

“All sharks have internal fertilization, like humans, where it happens inside the female’s body,” Frable said. “Other fish will release genetic material into the water as a method of reproduction. Some sharks give live birth, others will keep the egg in their body and the egg hatches inside the body.

“Horn sharks lay eggs. After mating, the female will have a fertilized egg and will deposit it in a rocky reef area. The eggs are unique among sharks because they have a corkscrew shape. Other shark eggs have a flat shape with tassels, and people tend to find them and call them mermaid purses. That’s the more common shape.”

Horn shark eggs are believed to be corkscrew-shaped so they can be wedged between rocks, protected from predators, until they hatch.  

“So the baby develops in the egg case, and when it is ready to hatch, it chews its way out like a baby bird pecking on its egg shell,” Frable said. “Once they are out of the egg case, the egg case will float away and can wash up on beaches.” 

Beach-goers find them “pretty regularly” and email Scripps Oceanography asking what they are, he said.

Mating season is February to April, and females will lay one or two eggs per day intermittently during that period. 

It isn’t known exactly how long horn sharks typically live, but an unverified record states they can live up to 25 years. 

The horn shark is known to stay in one geographic area its whole life, including most of Southern California and Baja, Frable said. 

“It is one of our many local shallow-water fish, and we’re really lucky that you can see a lot of them while snorkeling,” he said. “You can’t do that in a lot of the world.”