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Author: Girard, 1854

Field Marks:
The bold, saddled black colour pattern of this shark is unique.

Diagnostic Features:
Strong cusps and cusplets on almost all teeth, teeth not semimolariform, lateroposterior ones bladelike, with strongly oblique cusps. First dorsal fin with posteroventrally sloping posterior margin; pectoral fins broadly triangular in adults. Total vertebral counts 129 to 150. Colour grey or bronzy-grey above, white below, with bold, large, broad black saddle-marks, becoming light-centred in adults, and scattered large black spots.

Geographical Distribution:
Eastern North Pacific: from Oregon to Gulf of California, USA, and Mexico.

Habitat and Biology:
An abundant, cool to warm-temperate shark of inshore and offshore continental littoral waters, most common on or near the bottom in shallow water from the intertidal to 4 m depth, less common down to 91 m. The leopard shark is commonly found in shallow, enclosed, muddy bays, often entering them as the tide rises and departing when it retreats. It favours flat sandy areas, mud flats, and bottoms strewn with rocks near rocky reefs and kelp beds. This is an active, strong-swimming shark, usually seen inundulating motion, that forms large schools sometimes mixed with grey or brown smooth-hound sharks (Mustelus californicus and M. henlei) and piked dogfish (Squalus aranthiac). Movements are not well understood, and schools are apparently nomadic; they have been seen to appear in an area for a few hours and then disappear. In a tagrecapture ageing study initiated in 1979 with over 1100 leopard sharks tagged in San Francisco Bay off south San Francisco, Susan E. Smith of the U.S. National Marine Fisheries Service Tiburon Laboratory found that most of the sharks recaptured to date were recovered close to their tagging place, suggesting limited local movements; but that some managed to travel outside the Bay south about 150 km (S. Smith, pers. comm.). Leopard sharks are sometimes seen resting on the bottom by divers, on sand among rocks; and readily doso in aquaria.

This shark readily adapts to captivity, and can live over twenty years if captured when young. In captivity, it shows a strong preference for the bottom, although individuals will swim at midwater or at the surface. It is extremely hardy, and is one of the best sharks to keep in aquaria.

Ovoviviparous, without a yolk-sac placenta; number of young 4 to 29 per litter. S. Smith (pers. comm.), using sectioning technique to demonstrate the growth rings in the vertebrae of leopard sharks and tetracycline to calibrate the rings in sharks recaptured after being tagged, has found that these sharks are slow-growing, and as in the piked dogfish (Squalus acanthias) may take over a decade to mature.

The leopard shark is primarily an opportunistic feeder on bottom-dwelling animals with some littoral prey taken also; invertebrates are somewhat more important in its diet than fish prey. Items taken include cancrid, grapsid, and mole crabs; shrimp and ghost shrimp; clam siphons and sometimes feet and whole clam bodies; polychaete worms; a large, sausage-shaped echiuroid worm, the fat innkeeper or weenie worm (Urechis caupo), which can be the most frequent prey item in some localities; octopi; bony fishes, including anchovies, herring, topsmelt, croakers, surf perch, gobies, rockfish, sculpins, flounders, sanddabs, tongue-soles, and midshipmen (Porichthys); and small elasmobranchs, including brown smooth-hounds (Mustelus henlei), guitarfish (Rhinobatos productus), and bat rays (Myliobatis californicus). When available, the eggs of herring, topsmelt, jacksmelt, and midshipmen are avidly eaten by this shark. Crabs, shrimps, bony fish, fish eggs, clam necks and innkeeper worms are the most important prey items of leopard sharks.

There is considerable variation in the diet of the leopard shark with size and season in Elkhorn Slough, California (Talent, 1976). Juveniles below 70 cm feed mostly on crustaceans, primarily small crabs (especially grapsids), but as the sharks approach maturity other prey items increase in importance as crustaceans diminish. Fish are most heavily taken by adults over 130 cm, clam necks and fish eggs are most important to adults 110 to 130 cm, and innkeeper worms are most important to juveniles and adults 80 to 130 cm long. Young sharks feed heavily on grapsid crabs but prey more on larger cancrid crabs as they approach maturity. Small sharks feed mostly on crabs throughout the year while larger sharks show seasonal variation, primarily associated with the availability of fish eggs. Large sharks eat fish mostly during the summer, and fish eggs in winter through early summer when topsmelt, jacksmelt and herring spawn. Clams and crabs were most commonly taken in the autumn, with a shift in importance from grapsid to cancrid crabs and to innkeeper worms during winter and spring.

The common presence of mud-burrowing prey such as ghost shrimps, innkeeper worms, polychaetes, and clams (necks) suggest that these sharks actively feed very close to the mud or in it to a far greater extent that the sympatric brown smooth-hound (Mustelus henlei), which normally does not take clam siphons, rarely takes innkeeper worms, and captures polychaetes far less frequentlythan leopard sharks. The action of leopard sharks in taking clam siphons has not been seen, but although the clams protrude their siphons some distance from the mud, they are instantly retracted when disturbed, suggesting that the sharks must quickly seize and pull on them until the siphons break or are bitten off by their rather powerful jaws and small but sharp slicing teeth. Sometimes whole clam bodies are found as stomach contents, without shells; the shell removal method is not known, but one possibility is that the shark rips the clams free from their shells while tugging on their siphons, while another is that the shark violently shakes or rubs the shells off after extracting clams from the mud. Innkeeper worms do not leave their burrows but may protrude their bodies slightly, allowing the sharks to pull them out, but more likely the sharks are able to suck them out of their burrows since most of the worms are intact and without bite damage as stomach contents (Russo (1975); Talent (1976)).

Leopard sharks and piked dogfish have been observed catching anchovies together at the surface inside a hollow bridge-support structure in San Francisco Bay, slowly swimming counterclockwise into oncoming clockwisemoving, densely packed schools of anchovies with their mouths wide open (Russo, 1975). The sharks did not show any specific hunting behaviour or directed movements toward their prey but simply ingested any anchovies that blundered into their mouthsl See the account of the oceanic whitetip shark, Carcharhinus longimanus, for a similar observation with this species.

Eelgrass (Zostera) and marine algae have been found in the stomachs of several leopard sharks, probably taken incidentally by the sharks having fed on prey animals and fish eggs.

This shark was once recorded as harassing a diver with a nosebleed, but in general it is very wary and usually flees when approached underwater. It is generally regarded as harmless to people.

Size:
Maximum l80 cm, males maturing between 70 and 119 cm and reaching 150 cm, females maturing between 110 and 129 cm and reaching 180 cm, though most adults are smaller than 160 cm; size at birth about 20 cm.

Interest to Fisheries:
In California this species is commonly taken by sports anglers and spearfishers, but in recent years has come tobe increasingly taken by smallscale commercial line fisheries. In some areas of California it may be declining in numbers, due to increased pressure by spear and line-fishers. Mexican catches are little-known, but presumably occur. Its meat is excellent and is utilized fresh or fresh-frozen for human consumption.

Remarks:
The earliest name for this species is Triakis californica Gray, 1851, proposed without description and hence a nomen nudum unless the name of the species itself is considered a valid indication of its identity (that is, a member of the hitherto monotypic genus Triakis from California). The writer examined the five syntypes of Triakis californica, British Museum (Natural History) BMNH 1953.5.10.8-12 late fetuses, 160 to 173 mm long, from Monterey, California) and confirmed that they are indeed conspecific with T. semifasciata. However, even if T. californica is a valid name, it would not serve nomenclatural stability to replace the well-known and virtually universally used T. semifasciata.

Triakis felis Ayres, 1854 was published about one month (4 December 1854) later than T. semifasciatum Girard, 1854 (November, 1854, possibly on 14 November; Lillian P. Dempster, pers. comm.).

Type material:
Holotype: ? Type Locality: San Francisco, California, USA, near Presidio, San Francisco Bay.

Leopard shark (Triakis semifasciata)