Isurus oxyrinchus (Eastern North Pacific subpopulation)
|Scientific Name:||Isurus oxyrinchus (Eastern North Pacific subpopulation)|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Cailliet, G.M., Cavanagh, R.D., Kulka, D.W., Stevens, J.D., Soldo, A., Clo, S., Macias, D., Baum, J., Kohin, S., Duarte, A., Holtzhausen, J.A., Acuña, E., Amorim, A. & Domingo, A.|
|Reviewer(s):||Fowler, S.L., Dudley, S., Soldo, A., Francis, M. & SSG Pelagic Shark Red List Workshop participants (Shark Red List Authority)|
Analysis of longline survey data of mainly juvenile individuals off southern California suggests that the Shortfin Mako (Isurus oxyrinchus) catch per unit effort (CPUE) may be declining slightly. However, recent tagging and tracking data show that it is also highly migratory, both vertically and horizontally, thus making accurate or precise population estimates difficult. There is no evidence to suggest that the eastern north Pacific subpopulation has been sufficiently depleted to warrant “Vulnerable” status at the present time, and this subpopulation is considered Near Threatened as a precautionary measure.
|Range Description:||Eastern Pacific: USA (Washington and California) south to Mexico, Costa Rica, Ecuador, Peru and central Chile, from 20-50° between Australia and Chile, and to ~ 60° southeast of New Zealand.|
There are comparatively few records of pregnant females, especially in the eastern North Pacific. However, there are a large number of juveniles and young of the year fish in the southern California Bight indicating that it is a nursery area. In summer, the Southern California Bight is home to a large population of Shortfin Mako sharks (Klimley et al. 2002, Holts and Kohin 2003). Abundance surveys and fishing reports indicate that juvenile mako sharks appear in the Bight in spring when water temperatures rise above 16°C and may depart from the area in fall when water temperatures decline.
Native:Chile (Antofagasta, Coquimbo, Santiago, Valparaíso); Costa Rica (Costa Rica (mainland)); Ecuador (Ecuador (mainland)); Guatemala; Honduras (Honduras (mainland)); Mexico; Nicaragua (Nicaragua (mainland)); Peru; United States (California, Washington)
|FAO Marine Fishing Areas:|
Pacific – eastern central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||In the Eastern North Pacific, tagging studies have been carried out by the California Department of Fish and Game (Anon. 2001), and more recently by the National Marine Fisheries Service, Southwest Fisheries Science Center (Holts and Kohin 2003, Holts et al. 2004). Using a consistent sample size of 28 sets of 200 hooks during each of eight years (1994–1997, 2000–2003), catch per unit effort (CPUE) data showed a slight decline (Holts et al. (2004); y = -0.0696x + 1.0982, R2 = 0.5107). However, it does not appear to be sufficient to warrant serious concern about the population. The large horizontal (primarily north-south along the coastline, but with some inshore-offshore movements) (Holts et al. 2004) and vertical (up to ~ 500 m) (Holts and Kohin 2003; Sepulveda et al. 2004) movements of Shortfin Makos, a behavior that could make them more or less available to the gear spatially but not necessarily indicating a population decline. Likewise, for males and females, there appeared to be a slight increase in the average size caught over the same eight years (y = 1.8368x + 112.38, R2 = 0.3751). This, combined with the CPUE changes would suggest that the biomass indices had not changed. The variability among years in CPUE can also be attributed to inter-annual oceanographic and climate changes, especially water temperature (http://www.pcouncil.org/hms/hmsback.html). Thus, although there are no precise or accurate population estimates, it appears that the population of shortfin makos in the eastern north Pacific has been relatively stable. (Taylor and Holts 2001, PFMC 2003).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Habitat and movements|
The Shortfin Mako is an active, offshore littoral and epipelagic species, found in tropical and warm-temperate seas from the surface down to at least 500 m, seldom occurring where water temperature is <16°C (Compagno 2002). It is probably the fastest shark and is among the most active and powerful of fishes. Like other lamnid sharks, the Shortfin Mako,is endothermic using a heat-exchanging circulatory system to maintain muscle and visceral temperatures above that of the surrounding seawater allowing a higher level of activity (Carey et al. 1981, Bernal et al. 2001).This shark occurs well offshore but penetrates the inshore littoral just off the surf zone in some areas such as parts of KwaZulu-Natal, South Africa where the continental shelves are narrow. Off South Africa, shark meshing data suggests that this species occurs in clear to turbid water in water temperatures from 17–22°C. In the western north Atlantic it occurs in a similar range of temperatures, and only moves onto the continental shelf when surface temperatures exceed 17°C. In the eastern north Pacific, juveniles range into southern California waters and tend to be seen and caught near the surface. They appear to use these offshore continental waters as nursery areas (Taylor and Holts 2001). It was previously thought that they stay near the surface above 20 m depth, in waters between 20–21°C, seldom descending into cold subsurface waters below the thermocline (Holts and Bedford, 1992). However,this has been challenged by more recent tracking studies (summarized below).
Results from a large tagging study in the western north Atlantic show that Shortfin Makos make extensive movements of up to 3,433 km with 36% of recaptures caught at greater than 420 km from their tagging site (Casey and Kohler 1992). However, only one fish crossed the mid-Atlantic ridge suggesting that trans-Atlantic migrations are not as common as in blue sharks Prionace glauca.
Klimley et al. (2002) tracked three Shortfin Makos near La Jolla, California, for several days, and their movements were mainly offshore from the surface to 50 m. Holts and Kohin (2003) deployed pop-up archival tags on eight makos (118–275 cm TL) in June–July 2002 for 2–4 months. Pop-up locations ranged from 20–911 km from deployment locations. The sharks utilized near-shore and open-water areas off California and Baja California roughly between 23–43°N and out to 125°W. While the records indicate that greater than 90% of the time was spent above 50 m, several sharks showed a diurnal pattern of vertical excursions to beyond 200 m during daylight hours. Sharks frequently dove into water less than 10°C. These data demonstrate the range of habitats utilized by mako sharks and begin to shed light on their daily and seasonal behaviors. Sepulveda et al. (2004) found that seven tagged juveniles stayed near the surface at night, and went as deep as 200 m, mostly during the day. In addition, stomach temperatures were measured, indicating feeding occurred during the daytime, with meals taken during a dive causing stomach temperatures to drop noticeably.
Life History Parameters
The Shortfin Mako reaches a maximum size of about 4 m (Compagno 2001). Initial age and growth studies in the western north Atlantic suggested that two pairs of growth bands are laid down each year in their vertebral centra, at least in young shortfin makos (Pratt and Casey 1983). However, recent evidence using marginal increment analysis in Mexico (Ribot-Carballal et al. 2005) and bomb radiocarbon (Campana et al. 2002, Ardizzone et al. 2006) indicates that the alternative hypothesis (one pair of growth bands per year; Cailliet et al. 1983) is valid. Age at maturity has been determined recently in several populations, including New Zealand (7–9 years for males, and 19–21 years for females Bishop et al. (2006)), and the western north Atlantic (eight years for males, and 18 years for females (Natanson et al. 2006)). Longevity has been estimated as 29–32 years (Bishop et al. 2006, Natanson et al. 2006).
There is a large difference in size at sexual maturity between the sexes. In the northwest Atlantic, males reach maturity at about 195 cm and females at about 265–280 cm (Pratt and Casey 1983, Stevens 1983, Cliff et al. 1990). In New Zealand, males mature at 198–204 cm and females at 301–307 cm (Francis and Duffy 2005). Compagno (2001) reports males mature between 203–215 cm, reaching a maximum size of 296 cm, and females mature between 275–293 cm, reaching a maximum of almost 4 m.
The Shortfin Mako is ovoviviparous and oophagous, but what little is known of its reproductive cycle indicates the gestation period is 15–18 months, with a three year reproductive cycle (Mollet et al. 2000). Litter size is 4–25 pups (possibly up to 30, mostly 10-18), which are about 60-70 cm long at birth (Garrick 1967, Compagno 2001). There are comparatively few records of pregnant females. Among 26 shark species, the Shortfin Mako has an intrinsic rebound potential (a measure of its ability to recover from exploitation) in the mid-range (Smith et al. 1998). The annual rate of population increase is 0.046 yr-1 (S. Smith pers. comm.) Cortes (2002) calculated a finite rate of increase (lambda) of 1.141 (1.098 to 1.181 95% CI, r = 0.13) and the average reproductive age as 10.1 (9.2 to 11.1 95% CI) years.
The diet of Shortfin Makos has been reported to consist mainly of teleost fishes (including mackerels, tunas, bonitos and other scombrids, anchovies, herrings, grunts, lancet fishes, cod, ling, whiting and other gadids, salmon, yellowtails and other carangids, sea basses, porgies, swordfish) and cephalopods in studies from the Northwest Atlantic and Australia (Stillwell and Kohler 1982, Stevens 1984), while elasmobranchs were the most common prey category from Natal, South Africa (Cliff et al. 1990). A daily ration of 2 kg/day (based on an average weight of 63 kg) was estimated for makos in the northwest Atlantic (Stillwell and Kohler 1982). Large makos over (3 m in length) have very broad, more flattened and triangular teeth, perhaps better suited to cutting large prey than the awl-shaped teeth of smaller individuals (Compagno 1984a). There are several anecdotal accounts of makos attacking and consuming Broad-bill Swordfish (Xiphias gladius). It also eats sea turtles, dolphins, salps and occasionally detritus (Compagno 1984a).
|Movement patterns:||Full Migrant|
|Use and Trade:||
This is one of the most valuable shark species for its high quality meat. The meat is utilized fresh, frozen, smoked and dried-salted for human consumption; the oil is extracted for vitamins; the fins used for shark-fin soup; the hides are processed into leather and the jaws and teeth are used for ornaments (Compagno 2001).
Big-game sports angling for mako sharks is widespread, e.g. New Zealand, South Africa and California - see Threats section above for more information.
Makos have become the subject of ecotourism diving in recent years, with most of the mako dive sites being off southern California from the Los Angeles Basin to San Diego, but with sites also in South Africa and the Maldives (Compagno 2001).
Estimates of mako bycatch in various gillnet fisheries in the North Pacific are given in Bonfil (1994). Bycatch in the Japanese salmon fishery in 1989 was about 15 t, and about 63 t was taken in the squid fishery in 1990. In the Japanese large-mesh driftnet fishery in the South Pacific, about 286 t of Shortfin Mako was caught in 1990. The Spanish pelagic longline fishery for swordfish and sharks is expanding rapidly in the Pacific. Shortfin makos comprise about 5% (~600–700 t) of the total catch of this fleet (Mejuto et al. 2007).
Reported average catch rates for shortfin makos vary from 0.3-3.4 sharks per 1,000 hooks (Stevens and Wayte 1999). Stevens (in press) used stratified catch rates in conjunction with fishing effort and average weights to estimate a catch of 4,100 t caught by high-seas longlining in the Pacific in 1994. Longline fleets take about 100-200 t from around New Zealand each year (Ministry of Fisheries Science Group 2006) and about 100 t were taken in Australian EEZ waters by Japanese tuna vessels each season (Stevens and Wayte 1999).
A coastal driftnet fishery for juvenile shortfin mako shark developed during the late 1970s in California; landings reached 242 t in 1982, fluctuated between 102-278 t from 1983-91 and declined to less than 100 t after 1991 (Holts et al. 1998). An experimental coastal longline fishery targeting makos took between 50 and 120 t annually durung1988-91 before the fishery was closed. Bycatch will continue to be an issue in the drift gillnet and longline fisheries until effective measures are developed which reduce the bycatch to close to zero (Crooke 2001). Although makos are not targeted in these fisheries, they are kept as the third most valuable species. The shortn mako shark was taken by the high seas shark and swordsh drift longline shery, which developed between 1991 and 1994 (Taylor and Holts 2001) outside the US 200-nm Exclusive Economic Zone prior to its closure in spring 2004. A small portion of the catch was landed in California with annual landings ranging from 9,523 to 128,116 pounds between 1991 and 1999.
The present status of the Shortn Mako shark in state and federal waters off California is not known but is of some concern (Taylor and Holts 2001). This is mainly because adult mako sharks do not frequent California’s coastal waters. A possible threat to the mako population off California and in the eastern Pacic would be the potential for over-development of sheries within the coastal nursery. Therefore, continued efforts to monitor the shortn mako shark juveniles are needed.
Makos have long been prized game fish along the East Coast of the US (Taylor and Holts 2001). In the mid-to late-1980s, estimates of the number of California angler trips for sharks grew ten-fold from 41,000 to 410,000 annually: the principal target being Shortfin Mako. After the increase during the 1980s, the sport fishery has stabilized at a relatively high level. Total annual landings (sport and commercial) peaked in 1987 at 464,308 pounds and again in 1994 at 394,792 pounds. In both cases, landings declined rapidly in the two years following the peaks. Currently, commercial passenger fishing vessels run fishing trips on a regular basis from nearly all ports in southern California.
In Chile, the only target fishery for Shortfin Mako is a spring-summer longline fishery off the northern coast (Acuña et al. 2002). In Ecuador, there is evidence that catches of shortfin makos have declined from a high of 2,000 t in 1994 to lows approaching 100 t in 2000 and 2001 (Herrera et al. in press).
Off California, early juvenile shortfin makos were targeted by a short-lived experimental drift longline fishery and are a welcome bycatch in the driftnet fishery for swordfish (Cailliet et al. 1993, Compagno 2001). Up to 475 t of Shortfin Makos were taken jointly by these fisheries in 1987, and although CPUE did not show a declining trend there, concerns over the heavy exploitation of immature fish prompted the closure of the experimental longline fishery in 1992 (O’Brien and Sunada 1994, Compagno 2001). Total bycatch of Shortfin Makos in the former high-seas driftnet fisheries in the North Pacific in the early 1990s was estimated at about 360 t/y (Bonfil 1994, Compagno 2001). This species is apparently very common in the tuna fisheries of Indonesia: unconfirmed reports indicate that landings of shortfin makos from Indonesian waters attained 5 200 t in 1995 and that the estimated potential is about 16 000 t/y (Priyono 1998, Compagno 2001).
On the west coast of the US, declines in the coastal driftnet fishery taking thresher and Shortfin Makos led to management actions in 1985. Management now comprises of limited entry, mandatory logbooks, and specific time-area closures. An experimental longline fishery targeting shortfin makos was terminated (Hanan et al. 1993, Holts et al. 1998). Bag limits for recreational take of makos in California were introduced in 1991. The draft Highly Migratory Species Fishery Management Plan (PFMC 2003) indicates that the shortfin mako population is not overfished and they have set a harvest guideline of 150 t off California, Oregon and Washington. US west coast based longline fishing for swordfish is currently prohibited and expected to reopen in the fall of 2005 under new restrictions. The Hawaii based swordfish longline fishery recently reopened with restrictions aimed at preventing turtle mortalities. New Zealand included shortfin mako shark in its Quota Management System in October 2004.
In Chile, there are gear regulations for the shortfin mako artisanal fishery and since 2002 fishing areas and register of boats in the National Marine Service is required, the access to the fishery is also regulated (E. Acuña pers. comm.).
|Citation:||Cailliet, G.M., Cavanagh, R.D., Kulka, D.W., Stevens, J.D., Soldo, A., Clo, S., Macias, D., Baum, J., Kohin, S., Duarte, A., Holtzhausen, J.A., Acuña, E., Amorim, A. & Domingo, A. 2009. Isurus oxyrinchus (Eastern North Pacific subpopulation). The IUCN Red List of Threatened Species 2009: e.T161751A5496273.Downloaded on 17 December 2017.|
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