Taxonomy

Rarity

The leopard shark is common where it lives, and in one place along the California coast it is possible to see hundreds of them at once. From early summer into late fall, a large group of pregnant females gathers in the warm shallow water off La Jolla Shores in San Diego. In a study led by Andrew Nosal at the Scripps Institution of Oceanography, 97 percent of the sharks in the aggregation were female, and every one that was sampled was pregnant. The sharks return each year: about 74 percent of tagged individuals came back the following summer, and about 50 percent returned across 3 consecutive years. Outside the aggregation season, the shark is spread more thinly, and most divers encounter it as a single fish cruising the bottom in a bay or along a sandy beach.

The California population is considered secure. The species was assessed as Least Concern by the IUCN in 2014. That rating rests on a set of state fishery rules put in place in the early 1990s after commercial and aquarium-trade harvests began pulling numbers down. Since then, demographic models estimate the California population growing at 3 to 6 percent per year under current fishing rates. The animal is still slow-growing and stays put in small regional populations, which is what allows a local group to be knocked down quickly if fishing effort concentrates there.

Seasonality

Location

The leopard shark lives only in the eastern Pacific, from Coos Bay in Oregon south to Mazatlan on the Mexican mainland, and throughout the Gulf of California. It is a bottom-dwelling fish that spends most of its life in shallow water, and it is most abundant from the intertidal zone down to about 15 feet. Individuals have been recorded as deep as 300 feet, but that is unusual. The typical habitat is muddy or sandy flats inside enclosed bays and estuaries, along with the sandy edges around rocky reefs and kelp beds. The 9 known nursery grounds along the California coast include Humboldt Bay, Tomales Bay in Marin County, Bodega Bay in Sonoma County, San Francisco Bay, Elkhorn Slough in Monterey County, Morro Bay in San Luis Obispo County, Santa Monica Bay in Los Angeles County, Catalina Harbor at Catalina Island, and San Diego Bay.

The sharks live in loose, wandering schools that appear in an area for a few hours and then disappear. The schools tend to be sorted by age and sex, and they are not tied to a single reef or hole the way many other bottom fish are. A leopard shark counted at one beach today may be a mile away tomorrow. Genetic surveys along the California coast have identified 7 discrete gene pools between Humboldt Bay in Humboldt County and San Diego, which means individual sharks trade very little between regions even though the species ranges continuously along the coast.

The La Jolla Shores aggregation is the best-studied case of leopard shark movement. From June through December each year, mature pregnant females gather in the warmest available water inside the surf zone, and Nosal's acoustic-tagging study found the sharks spending about 70 percent of their time in the top 2 meters of the water column. The interpretation is that the warm shallow water functions as an incubation zone. Speeding up gestation in an ectotherm, an animal whose body temperature tracks the water it sits in, means faster development for the pups inside the mother. At night the sharks leave the surf line and swim into the head of the La Jolla submarine canyon, where they feed on market squid that come up out of the deep water to spawn.

Deep Dive

The leopard shark is a slender houndshark named for the pattern that runs down its back. On a silver-gray background it carries a row of dark saddles across the top, and dark spots that run along both flanks and the tail. Every adult wears the same basic pattern with slightly different spacing. The body is built for slow bottom feeding. It rarely reaches 6 feet in length, and the largest published record is about 6.5 feet. Weights top out around 40 pounds. The shark grows slowly at about 2 centimeters a year, and a large adult may be more than 20 years old, with a documented lifespan of at least 30 years.

The species is aplacental viviparous, which means the pups develop inside the mother, drawing nutrition from a yolk sac rather than a placenta, and are born live rather than as eggs. Gestation runs 10 to 12 months. Litters have run from 1 to 37 pups depending on the size of the female, and newborns come out at about 8 inches long. Males become mature at 7 to 13 years, females at 10 to 15. Only a single wild mating has ever been observed for this species: a 2004 encounter at La Jolla Shores, in water 1 to 10 feet deep, with 9 sharks gathered about 60 feet from the beach.

The diet is a bottom-feeder's list. Leopard sharks eat crabs, shrimp, small bony fishes such as anchovies, herring, topsmelt, croakers, surfperch, gobies, rockfish, sculpins, flatfish, and midshipmen, along with fish eggs, clams, and the fat innkeeper worm, a chubby pink worm that lives in a U-shaped burrow in the mudflats. They feed by opening the mouth wide and pulling in a rush of water that sucks prey off the bottom, with the jaws also shooting forward to grab. The teeth are small and blunt, arranged in an overlapping pavement. Documented predators of small leopard sharks are the great white shark and the broadnose sevengill shark.

A 2016 study of leopard shark navigation, led by the same Scripps team, tested how the sharks find their way back to shore after being displaced offshore. Sharks that had their nostrils blocked with cotton soaked in petroleum jelly took a much longer, wandering path back to the beach. Sharks with clear noses swam a nearly straight line home. The finding is that leopard sharks navigate by smell, an unusually direct piece of evidence for something long suspected in sharks generally.

The species is legal to take in California for sport, and the fishery is not small: recreational anglers landed an average of about 45,000 leopard sharks per year from 1993 forward, and commercial landings peaked in 1983 at just over 100,000 pounds. The recreational rules are a 36-inch minimum total length and a bag limit of 3 fish per person, open year-round except in the Groundfish Exclusion Areas, where leopard shark may not be taken. The 36-inch minimum was set in 1992, after a hook-and-line fishery aimed at newborn pups for the aquarium trade drew a state response. Most take today is by rod and reel from the surf, bays, and piers. The meat is described as good eating and is sold fresh and frozen. There is a health caution alongside that: leopard sharks living in developed bays accumulate mercury, pesticides, and polychlorinated biphenyls (PCBs) at levels the Florida Museum of Natural History calls high enough to advise against eating. Sharks and rays also concentrate urea in their tissues, which turns into ammonia after death and requires prompt bleeding and icing to avoid an off odor in the fillet.

The bulk of the animal's public presence in California comes through diving and snorkeling rather than fishing. The La Jolla Shores aggregation forms inside the boundary of the Matlahuayl State Marine Reserve, a no-take area, and during summer the sharks are within wading depth of the beach. The International Shark Attack File carries a single 1955 record for the species, with no significant injury. A snorkeler swimming among a hundred pregnant females sees no aggression. The animals hold their position or drift away as swimmers approach. That is the encounter that put the species on most Southern California divers' lists.

Where to Find Them

Beaches whose habitats match this species

Matched by habitat: a beach is listed when its biome tags overlap this species' biomes.