|Scientific Name:||Triakis semifasciata Girard, 1855|
Triakis semifasciatum Girard, 1855
|Taxonomic Source(s):||Eschmeyer, W.N. and Fricke, R. (eds). 2015. Catalog of Fishes: genera, species, references. Updated 1 October 2015. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 1 October 2015).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Carlisle, A.B., Smith, S.E., Launer, A.L. & White, C.F.|
|Reviewer(s):||Nosal, A.P. & Chabot, C.L.|
|Facilitator/Compiler(s):||Lawson, J., Walls, R.H.L., Ebert, D.A. & Dulvy, N.K.|
Leopard Shark (Triakis semifasciata) is one of the most common nearshore sharks along the Pacific coast of North America, ranging from Washington to Mazatlan, Mexico, including the Gulf of California. They appear to exhibit limited long distance movement, and as a result it is thought that the population consists of three regional population clusters in northern California, southern California and Mexico with limited genetic exchange.
In California, where nearly all of the U.S. harvest occurs, the Leopard Shark is taken primarily by recreational anglers, although it is also caught incidentally in commercial fisheries. The species has also been harvested for the cold-water aquarium trade and has been highly prized for its distinctive markings and hardiness. Due to its rather limited geographical range and 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 and exploitation rates. Additionally, current conservation and regulatory actions enacted by the California Department of Fish and Wildlife appear to have reduced these rates and have contributed significantly toward protecting this species from excessive harvesting in recent years and there is evidence that the leopard shark population has been increasing as a result of these management actions.
Little is known of the biology, historical population abundance and full extent of harvest of this species in Mexican waters, but it is estimated to be less than one percent of the Pacific Ocean catch off Baja California and rarely caught in the Gulf of California. 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 is assessed as Least Concern. However, due to the fact that this species is endemic to this region, is subjected to recreational fishing and bycatch pressures (albeit regulated in the U.S.), is susceptible to overfishing due to its life history characteristics (slow growing, long lived, late maturing, low productivity), and is impacted by habitat loss and degradation, it is important to continue managing and monitoring the species to ensure the health of the species.
|Previously published Red List assessments:|
|Range Description:||This is one of the most common nearshore sharks along the west coast of North America (Ebert 2003). In U.S. waters, the leopard shark is most abundant along the coast of California. Leopard Shark is endemic to the Northeast Pacific Ocean, ranging from Samish Bay, Washington to Mazatlan, Mexico, including the Gulf of California. In Oregon waters, Emmett et al. (1991) record this species only from Coos Bay, where it is listed as ‘rare’. They are commonly found in bays and estuaries, and have been reported from Coos Bay, Willapa Bay, Humboldt Bay, Tomales Bay, Bodega Bay, Bolinas Lagoon, San Francisco Bay, Elkhorn Slough, Morro Bay, San Pedro Bay, Alamitos Bay, Anaheim Bay, Newport Bay, Mission Bay, Bolsa Chica Lagoon, and San Diego Bay (Bane and Bane 1971, Emmet et al. 1991, Ebert 2003, Farrer 2009, Farrugia et al. 2014). They are also found along the open coast (Nosal et al. 2013a, 2014) and around offshore islands, such as the Channel Islands in southern California (Manley 1995, Ebert, 2003, Hight and Lowe 2007).|
Native:Mexico (Baja California, Baja California Sur, Sinaloa, Sonora); United States (California, Oregon)
|FAO Marine Fishing Areas:|
Pacific – northeast; Pacific – eastern central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||It is thought that the Leopard Shark population consists of regional stocks with limited connectivity (Smith and Abramson 1990, Lewallen et al. 2007). Lewallen et al. (2007) reported that there were seven subpopulations between Humboldt Bay and San Diego, with the Humboldt Bay population of leopard sharks being the most genetically distinct from the rest of the more southerly distributed populations. They also found some evidence of natal philopatry, which they suggest may be in part what drives the observed genetic structure. More recently, a genetic study of Leopard Shark from sample locations ranging from northern California to Mexico showed that distinct populations exist in northern California, southern California and Mexico (Barker et al. 2015). Within Mexican waters, the Pacific coast and Gulf of California stocks may be distinct populations (Smith 2001).|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Leopard Shark is a temperate shark of both inshore and offshore continental littoral waters, generally found on or near the bottom in shallow water from the intertidal to 20 m depth, although they have been found as deep as 156 m (Ebert 2003, Love 2011). This species is generally found over soft bottom habitats and around rocky reefs and kelp forests (Ebert 2003). Leopard sharks are relatively eurythermal and euryhaline species, but their distribution is known to be influenced by temperature, salinity, and dissolved oxygen levels (Hopkins and Cech 2003, Hight and Lowe 2007, Carlisle and Starr 2009, Dowd et al. 2010, Nosal et al. 2014). In their survey of Pacific coast estuaries, Emmet et al. (1991) reported that Leopard Shark of all age classes are commonly found in bays and estuaries between San Pedro Bay in Southern California and Humboldt Bay in Northern California, although they are particularly abundant in Elkhorn Slough, San Francisco Bay, Tomales Bay and Humboldt Bay. In southern California, they are known to form large aggregations in San Diego and the Channel Islands (Manley 1995, Hight and Lowe 2007, Nosal et al. 2013a, 2014).|
Leopard Shark 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, then during the winter they often move out of the bays to coastal waters as salinity and temperature decrease (Hopkins and Cech 2003, Carlisle and Starr 2009). In San Francisco Bay the population is mainly resident but about 10% move out of the bay in fall and winter (Smith and Abramson 1990). Leopard shark movements in bays and estuaries are strongly influenced by the tidal cycle. Leopard sharks will swim with tidal currents to reduce energetic costs associated with swimming as well as to facilitate foraging over a larger area (Ackerman et al. 2000, Carlisle et al. 2010). During incoming tides they move into shallow mudflats to forage and retreat to deeper water as the tide goes out (Ackerman et al. 2000, Carlisle and Starr 2009, Carlisle and Starr 2010). In exposed coastlines, tides have been shown to drive leopard shark movement between sand flats and rocky reefs (Nosal et al. 2013a). Leopard sharks have been reported to be more active at night (Manley 1995, Ackerman et al. 2000, Carlisle et al. 2010, Nosal et al. 2013a) as their rates of movement are generally higher at night. Manley (1995) reported that acoustically tagged leopard sharks at Santa Catalina Island, California, were more active at night, possibly related to foraging.
Leopard Shark appear to exhibit limited long distance movements, although they are capable of moving relatively large distances rapidly. One shark acoustically tagged at Catalina Island was detected seven days later along the mainland coast, a movement of approximately 105 km through deep water, after which it returned to Catalina Island (Hight and Lowe 2007). There have been several instances of sharks travelling ~100 km distance between Monterey Bay and San Francisco Bay and one shark tagged in San Francisco Bay was recaptured ~600 km away in Santa Monica Bay in southern California 10 years later, but in general, large scale movements appear to be limited (Smith 2001). This is supported by studies that have demonstrated that there is limited genetic exchange between Leopard Shark along different parts of the coast (Lewallen et al. 2007, Barker et al. 2015) and studies that have shown a high degree of site fidelity and potential natal philopatry, with many individuals consistently returning to particular locations (Lewallen et al. 2007, Carlisle and Starr 2009, Nosal et al. 2014, Barker et al. 2015).
Leopard sharks are viviparous, without a yolk sac placenta, and the female produces from 7 to 36 offspring in an annual reproductive cycle. Gestation time is 10-12 months, and size at birth is 17 to 25 cm total length (TL; Ackerman 1971, Kusher et al. 1992, Smith 2001). 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. 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). Maximum age is at least 25 years, but is estimated to be about 30 years with an estimated generation time of 18.5 years (Cortes 2002).
Pregnant females are believed to exhibit behavioural thermoregulation and aggregate in shallow warm habitats, likely to accelerate embryonic development (Hight and Lowe 2007, Nosal et al. 2013a, 2014). Bays and estuaries appear to be important nursery areas, particularly in central and northern California. Reported nursery areas include Humboldt Bay, San Francisco Bay, Tomales Bay, Bodega Bay, Elkhorn Slough, San Diego Bay and Catalina Harbor (Eigenmann 1891, Bane and Bane 1971, Talent 1985, Smith 2001, Ebert 2003, Carlisle et al. 2007), although Emmet et al. (1991) also reported the presence of juveniles in Morro Bay, Santa Monica Bay, and San Pedro Bay. In central and northern California, parturition appears to occur from March through September, with a peak in April and May (Ackerman 1971, Talent 1985, Smith and Abramson 1990, Ebert and Ebert 2005). In southern California pupping is believed to occur around May and June, although it has been reported to occur as late as September in San Diego Bay (Eigenmann 1891, Smith 2005). Mating is believed to occur shortly after pupping (Ackerman 1971, Talent 1985, Ebert 2003) and has only been observed once in the wild, in the shallow surf zone in La Jolla (Smith 2005). Females may mate with multiple males with as many as 36% of litters having multiple paternity (Nosal et al. 2013b).
Females generally give birth in shallow protected habitats, often over sand or mudflats (Love 2011). In central and northern California, neonates and juveniles are often found in more sheltered, shallow, inshore areas such as bays, mudflats, and tidal creeks (Barry and Cailliet 1983, Carlisle and Starr 2009). In Humboldt and San Francisco Bay, females have been observed releasing their young in beds of eel grass (Ebert 2003, Ebert and Ebert 2005). In southern California pupping and nursery areas are generally thought to be in the surf zone and sheltered coves of more open coast habitats (Smith 2001, Ebert 2003, Hight and Lowe 2007, Nosal et al. 2013). Leopard sharks have been observed giving birth in Catalina Harbor over sandy bottom in water as shallow as 1 m, with pups found in water only 0.3 m deep (Smith 2001).
|Generation Length (years):||25|
|Use and Trade:||This species is collected and traded for aquariums.|
Leopard Sharks appear to be primarily caught in Californian waters. 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, Pacific Fisheries Information Network (PacFIN), Recreational Fisheries Information Network (RecFIN)).
In California, where nearly all of the U.S. harvest occurs, the leopard shark is taken primarily by recreational anglers. The recreational leopard shark catch is much more extensive than the commercial catch for this species. Leopard sharks have been recreationally harvested by angling with baited hooks from piers, jetties, beaches, banks and skiffs, bow fishing in shallow waters, and spearfishing by divers. Estimated recreational landings in California between 1980 and 1995, for years when data were collected, averaged over 138 metric tons (mt) annually. After a peak in 1987 of around 546 mt, recreational landings declined and from the mid 1990’s to 2006 remained relatively lower and stable at around 46 mt (PacFIN, Smith and Horeczko 2006). Since 2006, recreational catch has decreased from prior levels (RecFIN).
Commercially, leopard sharks are taken incidentally in gillnet, longline and trawl fisheries although there is a small targeted hook-and-line fishery in San Francisco Bay (Smith and Horeczko 2006). 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 4.2 mt in 1958 to a high of 46 mt in 1983. Catches declined after 1983 and from the mid 1990’s to 2007 remained relatively low and stable, at around 11.4 mt. Landings dropped after 2008 and have remained low at around 2.3 mt per year since (http://pacfin.psmfc.org). Curtailment of inshore gillnetting probably contributed greatly to the decline in California landings. The species has also been harvested for the cold-water aquarium trade and is highly prized for its distinctive markings and hardiness (Smith and Horeczko 2006).
Loss and alteration of habitat, especially in coastal bays and estuaries, is of great concern for this species, given the importance of these areas for foraging and as nursery sites (Carlisle and Starr 2009). Water quality in bays and estuaries is of potential concern as well. For example, Elkhorn Slough, an important foraging and nursery area for this species, has experienced severe nutrient loading from surrounding agricultural areas, resulting in eutrophication and hypoxic conditions, which impact habitat and prey availability (Hughes et al. 2013). This is a potential problem as there is evidence that dissolved oxygen levels may influence habitat availability of this species (Carlisle and Starr 2009). Leopard sharks have also been shown to have significant concentrations of contaminants in their tissues, but the impact of this on their fitness remains unknown (Schaffer et al. 2006, Carlisle et al. 2007).
Resident stocks near large population centres may be particularly vulnerable to heavy localized fishing pressure due to the limited exchange among regional stocks (Smith and Abramson 1990, Lewallen et al. 2007, Barker et al. 2015). 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 fisheries management measures appear to have reduced these rates.
Poaching of pups for the aquarium trade has been a significant problem. In 2006, several individuals were arrested for illegally harvesting Leopard Shark pups for the aquarium trade. Investigators estimated that between 20,000 to 25,000 pups were poached from San Francisco Bay and 30,000 to 33,000 pups were poached from southern California between 1992 and 2003. This level of harvest is quite large when compared to recreational and commercial fishery Leopard Shark landings, with potentially important ramifications to Leopard Shark populations (Smith and Horeczko 2006).
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 catch off the Pacific coast of Baja California is comprised of this species (Cartamil et al. 2011) and most of the shark catch in the central Gulf of California fishery is comprised of other, larger species (e.g., Alopias and Carcharhinus spp.; Bizzarro et al. 2009). However, the historical abundance of Leopard Sharks in this region is also unknown.
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 for Leopard Shark (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 (Cailliet 1992, Au and Smith 1997), especially considering that they are caught in both commercial and recreational fisheries and considered to be a desirable food fish.
The leopard shark is one of the many species that has been considered, but is not now actively regulated, under the Pacific Fishery Management Council’s Groundfish Management Plan. Regulatory actions enacted by the California Department of Fish and Wildlife (CDFW) have contributed significantly toward protecting this species. 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 1 January 1992, establishing a 36 inch (91 cm) minimum size and a daily bag limit of three fish. The recreational fishing sector not only strongly supported the move, but also did much to promote it. Effective 1 January 1993, an 18 inch (45.7 cm) minimum size limit was extended to the commercial fishery for Leopard Shark and all sharks and rays, to prevent over-harvesting for the aquarium trade.
Additionally, California has general restrictions on usage of certain types of commercial gear (in particular gillnets) in the near shore zone, which offers a good degree of protection for the Leopard Shark. CDFW’s imposition of recreational and commercial fishing regulations appears to have halted the increase, if not reduced, total fishing mortality over the past decade (Smith et al. 1998). Indeed there is evidence that Leopard Shark have rebounded since regulations were implemented (Pondella and Allen 2008).
|Citation:||Carlisle, A.B., Smith, S.E., Launer, A.L. & White, C.F. 2015. Triakis semifasciata. The IUCN Red List of Threatened Species 2015: e.T39363A80672743.Downloaded on 21 September 2017.|