|Scientific Name:||Triakis semifasciata|
|Species Authority:||Girard, 1855|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Carlisle, A. & Smith, S.E.|
|Reviewer(s):||Ebert, D.A., Stevens, J., Pollard, D.A., Dudley, S. & Valenti, S.V. (Shark Red List Authority)|
This is one of the most common nearshore sharks along the Pacific coast of North America, ranging from Oregon to Mazatlan, Mexico, including the Gulf of California. It is commonly found in bays and estuaries, but also occurs along the open coast and offshore islands, usually at shallower depths but at times down to 91 m. In California, where nearly all of the US catch is taken, the leopard shark is taken primarily by recreational anglers. The species has also been captured for the cold-water aquarium trade and is highly prized for its distinctive markings and hardiness. Because of its rather limited geographical range and evidence of only limited exchange among regional stocks, resident stocks near large population centres may be particularly vulnerable to heavy localized fishing pressure. However, this species does not appear to be at risk judging by the combined landings in relation to previously calculated estimates of fishing mortality (mean F=0.084) and exploitation rates (mean E=0.075). Additionally, current conservation and regulatory actions enacted by the State of California appear to have reduced these rates and have contributed significantly toward protecting this species from excessive catches in recent years. Little is known of the biology and full extent of harvest of this species in Mexican waters, but it is estimated that less than one percent of the Pacific Ocean catch off Baja California under the category of "small sharks" is comprised of this species. As a result of the success of the conservation measures taken in the U.S. and the lack of a significant fishery in Mexican waters, this species has been classified as Least Concern. However, because it is endemic to this region, is subjected to fishing/bycatch pressures (albeit regulated in the U.S.), and has been shown to be susceptible to overfishing due to its life history characteristics (slow growing, long lived, late maturing, low productivity), it is important to continue managing and monitoring the species to ensure the health of the population.
|Range Description:||Northeast and eastern central Pacific: Oregon, USA to Mazatlan, Mexico, including the northern Gulf of California (Ebert 2003). This species is commonly found in bays and estuaries (including Elkhorn Slough, Drakes Estero, and San Francisco, Tomales, Humboldt, Morro, Santa Monica, San Pedro, Alamitos, Anaheim, Newport, Mission, and San Diego Bays in California) but is also found along the open coast and around offshore islands (Monaco et al. 1990, Ebert 2003).|
Native:Mexico (Baja California, Baja California Sur, Sinaloa, Sonora); United States (California, Oregon)
|FAO Marine Fishing Areas:||
Pacific – eastern central; Pacific – northeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This is one of the most common nearshore sharks along the west coast of North America. It is thought that the population consists of regional stocks with limited exchange (Smith and Abramson 1990). Centers of abundance in U.S. Pacific coast estuaries appear to be Elkhorn Slough, and San Francisco, Tomales, Humboldt, Morro, Santa Monica, and San Pedro bays in California. In Oregon waters, Emmett et al. (1991), in their survey of Pacific coast estuaries recorded this species only from Coos Bay, where it is listed as "rare". According to port samplers (ODFW, Seabourne pers. comm.), it seldom enters the Oregon commercial and recreational catch. In Mexican waters, the Pacific coast and Gulf of California stocks may be disjunct populations, since there are few taken in the southern Gulf of California (Carlos Villavicencio pers. comm.).|
|Habitat and Ecology:||
This shark occurs in cool to warm temperate waters, both inshore and offshore (Compagno in prep). It is most often found on or near the bottom in shallow water from the intertidal to 20m depth, and less commonly down to 91m depth, in flat sandy areas, mud flats, and bottoms strewn with rocks near rocky reefs and kelp beds (Compagno in prep). The leopard shark is commonly found in shallow, enclosed, muddy bays, often entering them as the tide rises and leaving when it retreats (Compagno in prep).
Leopard sharks are viviparous, without a yolk sac placenta, and the female produces from 4 to 36 offspring in an annual reproductive cycle. Gestation time is 12 months, and size at birth is 17 to 25 cm TL (Ackerman 1971, Compagno 1984, Kusher 1987, Kusher et al. 1992, Smith 2001, Compagno in preparation). Age at maturity for females is between 10 and 15 years and 105 to 135 cm TL. Males mature between 7 and 13 years and at 100 to 105 cm TL. Maximum age is at least 24 yrs, but is estimated to be about 30 years, and the maximum size is 198 cm TL with reports of sharks up to 213 cm TL (Miller and Lea 1972, Feder et al. 1974, Kusher et al. 1992, Smith et al. 2003). Leopard sharks grow slowly, reportedly averaging less than 2.2 cm per year, with fish of the same age varying greatly in size (Kusher et al. 1992). The fastest growth takes place prior to maturity; large fish are particularly slow growers, e.g., a 125 cm fish released in September 1979 in San Francisco Bay measured only 129 cm when it was recaptured in November 1991 at Santa Cruz--gaining only 4 cm in twelve years (S.E. Smith unpublished data).
Bays and sloughs appear to be important nursery areas in the north. Reported nursery areas include San Francisco Bay, Tomales Bay, Elkhorn Slough, Humboldt Bay, San Diego Bay, Catalina Harbor, and Bodega Bay (Eigenmann 1891, Bane and Bane 1971, Talent 1985, Smith 2001, Ebert 2003). In San Francisco Bay and Elkhorn Slough, California, parturition appears to occur from March through September, with a peak in April and May (Ackerman, 1971, Talent 1985, Smith and Abramson 1990). It also reportedly occurs between March and July in Humboldt Bay, Tomales Bay, Morro Bay, Santa Monica Bay and San Pedro Bay (Monaco et al. 1990). In San Diego Bay parturition is reported as occurring in September (Eigenmann, 1891). In Humboldt and San Francisco Bay, females have been observed releasing their young in beds of eel grass (Ebert 2003), while in southern California females are thought to release their pups along more open coastal areas, and have been observed giving birth to young in water 1m in depth over a shallow flat in Catalina Harbor, the pups milling about in water only 0.3 m deep (Smith 2001). Newly born pups are reportedly found in northern California bays and sloughs in April and May; also in the shallow surf zone in more southerly areas such as Santa Monica Bay in southern California around late May and June where they were harvested by hook and line for the aquarium trade in the late 1980s and early 1990s (S.E. Smith pers. obs. 1991). Juveniles are often found in more sheltered, shallow, inshore areas such as bays, mudflats, and tidal creeks (Barry and Cailliet 1983).
This shark is an opportunistic benthic feeder, devouring a variety of invertebrates and fishes, including the fat innkeeper worm (Urechis caupo), crustaceans (grapsid crabs and shrimp), clam siphons, teleosts, fish eggs, and small elasmobranchs. They may disturb the mud and use suction to capture prey. Their diet shifts with the season and the size of the shark (Russo 1975, Talent 1976, Ebert 2003). Pups caught in the surf zone along sandy ocean beaches in southern California reportedly feed heavily on sand crabs and presumably other sandy-bottom invertebrates. Predators on leopard sharks include the sevengill shark (Notorynchus cepedianus), and the great white shark (Carcharadon carcharias); man is probably the most important predator.
Strong swimming and nomadic, they are known to suddenly appear in an area, and then move on - possibly in relation to feeding or reproductive behaviour. They often occur in schools, sometimes with smoothhounds, spiny dogfishes, sevengills, and bat rays. Schools are often segregated by sex and size, and newborn leopard sharks have been observed to form loose schools (Feder et al. 1974; Ebert 2003). They are seasonally abundant in bays and estuaries (such as Elkhorn Slough, Humboldt Bay, Tomales Bay, Bodega Bay, and San Francisco Bay) during the spring and summer, and during the winter they often move out of the bays to coastal waters, likely as a result of decreased salinity and temperature due to winter storms and rain. In San Francisco Bay, California, the population is mainly resident but about 10% move out of the bay in fall and winter (Smith and Abramson 1990, Hopkins 1993, Ebert 2003). Their movements in several bays are strongly correlated to tides. During incoming tides they move into shallow mudflats to forage and retreat to deeper water as the tide goes out (Ackerman et al. 2000, Ebert, 2003). They appear to exhibit limited long distance movement. There have been several instances of sharks travelling between Monterey Bay and San Francisco Bay, and one shark tagged in San Francisco Bay was recaptured in Santa Monica Bay in southern California 10 years later, but in general movements appear to be limited (Smith 2001).
Along beaches in southern California it is not uncommon to observe large groups of leopard sharks in or just beyond the surf zone. Generally timid and wary around divers, this species is not considered dangerous, though there is a recorded minor attack on a skin diver in 1955 in California (Feder et al. 1974). Groups confined in aquaria have been observed to form a loose social hierarchy, where larger individuals assert dominance over smaller ones by gentle pectoral fin nipping (Smith pers. obs. 1979).
In California, where nearly all of the US catches occur, the leopard shark is taken primarily by recreational anglers. It is considered a desirable food fish. Over the past two decades, leopard sharks have been harvested by angling with baited hooks from piers, jetties, beaches, banks and skiffs; spearfishing by divers; commercial gillnetting along the coast; and commercial longlining. Some fish are taken incidentally in ocean bottom trawl nets. The species has also been captured for the cold-water aquarium trade and is highly prized for its distinctive markings and hardiness (commercial collectors C. Winkler and F. Nielson pers. comms). There have also been reports of illegal poaching of juvenile leopard sharks for the aquarium trade, for example from San Francisco Bay (Anon 2006).
The commercial and recreational catch of leopard sharks in the extreme northerly part of its range in Oregon is thought to be negligible (Emmett et al. 1991, Seabourne, Oregon Dept. Fish and Wildlife pers. comm. 1999).
A problem exists in accurately judging the extent of the commercial harvest because an unknown portion of the commercial catch may be landed under the general category "shark, unspecified" and different species are often marketed under the generic name "shark". California commercial landings specifically reported under the "leopard shark" category are relatively minor, and have ranged from 9270 pounds (4.2t) in 1958 to a high of 101 417 (46t) pounds in 1983. Curtailment of inshore gillnetting in the San Francisco/Monterey Bay area probably contributed to a decline in California landings after 1986 (Smith 1992).
The recreational leopard shark catch is much more extensive than the commercial catch reported specifically for this species. Estimated sport landings in California between 1980 and 1995, for years when data were collected, averaged over 304 000 pounds (138t) per year (US Dep. Commerce, Pacific Coast Marine Recreational Fisheries Statistics Survey, W. Buskirk pers. comm.).
Habitat loss could potentially be a problem, as bays and estuaries, which are often used as nursery grounds, are being greatly altered and destroyed through development, agriculture, aquaculture, pollution, etc, throughout the range of the leopard shark. However, the dependence of leopard sharks on these habitats has not been evaluated.
The size of the California leopard shark population has not been estimated, but considerable work has been done on its biology and population dynamics. In 1990, tagging and other life history data were used to estimate fishing mortality, yield, and stock replenishment rates to determine the degree of vulnerability to fishing pressure (Smith and Abramson 1990). Researchers indicated that, given the amount of fishing pressure exerted in the 1980s and that leopard sharks are more susceptible to overexploitation than previously thought, some measure of protection was necessary to assure replenishment of the population (Au and Smith 1997).
Because of its rather limited geographical range and evidence of only limited exchange among regional stocks within this range (Smith and Abramson 1990), resident stocks near large population centres may be particularly vulnerable to heavy localized fishing pressure.
Even though the commercial catch may be under-estimated because of reporting problems, this species does not appear to be at risk judging by the combined landings in relation to previously calculated estimates of fishing mortality (mean F=0.084) and exploitation rates (mean E=0.075) (Smith and Abramson 1990). Additionally, current management measures appear to have reduced these rates (see below).
Little is known of the biology and full extent of harvest of this species in Mexican waters, but it is estimated that less than one percent of the Pacific Ocean catch off Baja California under the category of "small sharks" is comprised of this species (Villavicencio pers. comm.) and most of the shark catch in the central Gulf of California fishery is comprised of other, larger species (e.g., Alopias, Carcharhinus and Sphyrna spp., (Villavicencio et al. 1996).
The Leopard Shark is one of the many species considered, but not now actively regulated, under the Pacific Fishery Management Council's Groundfish Management Plan (PFMC 1982).
Regulatory actions enacted by the State of California have contributed significantly toward protecting this species in recent years. In 1991, efforts increased to protect the leopard shark in California, and late that year California established new sport fishing regulations which took effect on January 1, 1992, establishing a 36-inch (91cm) minimum size and a possession limit of three fish. The recreational fishing sector not only strongly supported the move, but also did much to promote it. Effective January 1, 1993, an 18-inch (45.7cm) minimum size limit was extended to the commercial fishery for leopard sharks and all sharks and rays, to prevent over-harvesting for the aquarium trade (State of California 1996).
Commercial sportfishing boat catches of leopard shark in California have dropped from an average of 6.8 fish per trip between 1980-91 to an average of 4.0 fish after the size limit was imposed 1992-95, as more fish are being released (Kevin Hill pers. comm.). Also encouraging is evidence that mortality from hooking injuries is quite low (Smith and Abramson 1990).
Additionally, the state has general restrictions on usage of certain types of commercial gear in the near shore zone, which offers a good degree of protection for the leopard shark, at least for the present time.
The State of California?s imposition of a sport and commercial fishing size limit and general curtailment of gillnetting within this slow-growing species' near shore range appears to have halted the increase if not reduced total fishing mortality over the past decade (Smith et al. 1998).
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Ackerman, L.T., Kondraieff, M.C. Matern, S.A. and Cech, J.J. 2000. Tidal influence on spatial dynamics of leopard sharks, Triakis semifasciata, in Tomales Bay California. Environmental Biology of Fishes 58: 33-43.
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|Citation:||Carlisle, A. & Smith, S.E. 2009. Triakis semifasciata. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 02 September 2014.|