|Scientific Name:||Isurus oxyrinchus (Atlantic subpopulation)|
|Species Authority:||Rafinesque, 1810|
|Red List Category & Criteria:||Vulnerable A2bd+3bd+4bd 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)|
In the north Atlantic, Shortfin Mako (Isurus oxyrinchus) have likely undergone a decline in abundance (estimates based on logbook records ranging between 33 and 50%, demographic modeling suggesting a decline between 20 and 80%). In the northeast Atlantic landings data are not available for some countries, but the species is taken as a bycatch of the pelagic fishery. The area around the Strait of Gibraltar is thought to be a nursery area; most specimens caught there are juveniles. This area is heavily fished by the swordfish longline fleet. European Union (EU) vessels fishing for small pelagic species off the west coast of Africa are also known to take unquantified elasmobranch bycatch, including Shortfin Mako. There is no evidence of overfishing in the south Atlantic although data there are sparse and pelagic fishing pressure high. In the southwest Atlantic, Shortfin Mako is caught as bycatch in the pelagic longline fishery targeting mainly swordfish and tuna. Logbooks and landing data presented by, Brazil and Uruguay at ICCAT’s Sharks Sub-committee meeting in July 2007, show a decreasing trend in the catch per unit effort (CPUE) values since 2003. Given the apparent decline in abundance in the north Atlantic, the trends of the CPUE values in the southwest Atlantic and high fishing pressure from pelagic fleets throughout the Atlantic, this species is assessed as Vulnerable in the Atlantic.
|Range Description:||Western Atlantic: Grand Banks (Canada) to Uruguay and northern Argentina, including Bermuda, Gulf of Mexico and Caribbean. Eastern Atlantic: Norway, British Isles and Mediterranean to Morocco, Azores, Western Sahara, Mauritania, Senegal, Côte d’Ivoire, Ghana, southern Angola, probably Namibia, and South Africa (west coast).
Casey and Kohler (1992) suggest that the core distribution in the western north Atlantic is between 20° and 40°N, bordered by the Gulf Stream in the west and the mid-Atlantic ridge in the east (see Habitat and Ecology section for more details). Shortfin Mako in Atlantic Canadian waters represent the margins of the distribution of the population (Campana et al. 2005). In the eastern north Atlantic, it is presumed that the Straits of Gibraltar are nursery grounds (Buencuerpo et al. 1998 and Tudela et al. 2005).
The area between 17° and 35°S off the coast of Brazil is an area of birth, growth and mating (Amorim et al. 1998). Pregnant females with near term embryos have been found there, but not females in early pregnancy stages (Costa et al. 1995, Costa 1994). The presence of this species in Uruguayan waters year round has been confirmed by the observers on board the Uruguayan tuna fleet. Although a few new borns were captured, no pregnant females have been found (Domingo pers. comm. 2008).
Native:Anguilla; Antigua and Barbuda; Argentina; Aruba; Bahamas; Barbados; Belize; Bermuda; Brazil; Canada (Newfoundland I, Nova Scotia); Cayman Islands; Colombia (Colombian Caribbean Is.); Costa Rica (Costa Rica (mainland)); Côte d'Ivoire; Cuba; Curaçao; Dominica; Dominican Republic; France (France (mainland)); French Guiana; Gambia; Ghana; Gibraltar; Guadeloupe; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras (Honduran Caribbean Is., Honduras (mainland)); Ireland; Jamaica; Martinique; Mauritania; Mexico (Campeche, Veracruz, Yucatán); Montserrat; Morocco; Namibia (Namibia (main part)); Netherlands Antilles (Bonaire, Netherlands Leeward Is.); Nicaragua (Nicaragua (mainland), Nicaraguan Caribbean Is.); Norway; Panama; Portugal (Azores, Portugal (mainland)); Puerto Rico (Puerto Rico (main island)); Saint Barthélemy; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Pierre and Miquelon; Saint Vincent and the Grenadines; Senegal; Sierra Leone; South Africa (North-West Province, Western Cape); Suriname; Trinidad and Tobago; Turks and Caicos Islands; United Kingdom (Great Britain, Northern Ireland); United States (Florida, Georgia, Louisiana, Maine, Maryland, New Hampshire, New Jersey, New York, North Carolina, South Carolina, Virginia); Uruguay; Venezuela, Bolivarian Republic of (Venezuela (mainland), Venezuelan Antilles); Virgin Islands, British; Virgin Islands, U.S.; Western Sahara
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western central
|Range Map:||Click here to open the map viewer and explore range.|
Shortfin Mako in the north and the south Atlantic constitute genetically distinct groups (Heist et al. 1996). Casey and Kohler (1992) hypothesized from tag-recapture data that western north Atlantic makos form a separate population from those in the eastern Atlantic although limited intermixing is possible as shown by crossings to the Azores and Europe. Mitochondrial DNA data indicate separation of female makos between the western and eastern north Atlantic, but a lack of differentiation in nuclear DNA suggests male mixing across the North Atlantic (Heist et al. 1996, Schrey and Heist 2003). For fishery assessment purposes, mixing between the western and eastern north Atlantic is considered minimal.
Mature males were occasionally caught in the western English Channel in the 1960s and 1970s but are now rarely encountered (J.D. Stevens, pers. comm.), suggesting possible range contraction in the north-east Atlantic.
Analyses of CPUE from US pelagic longline fishery logbooks reported that Isurus species may have declined by about 40% in the northwest Atlantic between 1986 and 2000 (Baum et al. 2003). A more recent assessment of observer data for the same fishery found a similar instantaneous rate of decline of 38% between 1992 and 2005 (Baum et al. in prep). A similar analysis of the same dataset and species grouping that restricted the areas of analysis to account for unbalanced observations, resulted in an overall decline of 48% from beginning to end of the time series (1992-2005; Cortes et al. in press). A 2004 ICCAT stock assessment workshop reported that stock depletions for North Atlantic shortfin mako are likely to have occurred based on CPUE declines of 50% or more. Demographic model results varied widely, with one approach suggesting present stock size is about 80% of virgin level, and another approach suggesting reductions to about 30% of virgin biomass (1950s) (Cortes et al. in press).
In the south Atlantic, the magnitude of decline appears to be smaller than in the North Atlantic and the stock size appears to lie above MSY, although only one modeling approach could be applied to the available data and assessments results were more uncertain than for the North Atlantic.
For both north and south Atlantic populations, uncertainties about demographic parameters and catches, and the uninformative nature of available catch data indicate that further analysis is necessary to properly delineate stock status. If historical Shortfin Mako catch is higher than the estimates in this report, the likelihood of the stock being below the biomass at MSY will surely increase (ICCAT 2005). A standardized catch rate index from the commercial large pelagic fishery off Canada suggested a decline in the 1970s and stable abundance since 1988 (Campana et al. 2005). However, the analysis did not have the statistical power to detect anything less than a severe decline and these sharks represent the margins of the population. The most heavily fished areas lie outside of Canadian waters. The median size of mako sharks in the commercial catch has declined since 1988, possibly indicating a loss of larger sharks (Campana et al. 2005).
Off Brazil, the highest and lowest catches of Shortfin Mako from Santos longliners were 235 and 29 t from 1971–2001. The CPUE and average weight decreased from 4.5 to 4.1 kg/1,000 hooks and 60 to 37.3 kg respectively (Amorim et al. 2002). About 20 t/yr were caught by gillnetters in southern Brazil between 1993–94 (Jorge Kotas, pers comm, CEPSUL-IBAMA, Brazil). The unstandardised CPUE in the Uruguayan longline fleet was low and stable (average 35 kg/1000 hooks) from 1983 to 1998 and has increased steadily to 2004 (185 kg/1,000 hooks), lower in 2005 (90 kg/1,000 hooks) (ICCAT data). According to Mourato et al. (in press), based on the landings records and logbooks from the Sao Paulo fleet operating off Southern Brazil, the standardized CPUE for the period 1971–2006 was fluctuating but showed a slight decline. In contrast, the standardization of the CPUE of 29 years in the Brazilian tuna longline fleet showed a slight upward trend (Hazin et al. in press). In Uruguay, the total captures oscillated through the years, mainly in low values (8 to 21 tons per year), and reached maximum values in 2003–2005 (up to 200 tons per year) (Domingo 2002, Domingo et al. 2008). The standardization of the mako shark CPUE in the Uruguayan pelagic longline fleet for the period 1981-2006 show a slight increase between 1989 and 2003, and a decreasing trend towards 2006 (Pons and Domingo in press).
Shortfin Mako contribute some 9.5% to 10% of the pelagic sharks caught by Spanish longline fleets (targeting sharks and swordfish) in the Atlantic and Pacific Oceans (Mejuto et al. 2002, 2005, 2006, 2007).
|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).
Shortfin Makos have been caught in large numbers particularly on the high seas in pelagic longline fisheries, but also in other commercial pelagic fisheries and recreational fisheries. The first longline fisheries were prosecuted by Japan in western equatorial waters beginning in 1956 (Uozumi and Nakano 1996). The fleet expanded rapidly in the 1960s, and covered almost the entire Atlantic by the late 1960s (Bonfil 1994), including the areas currently fished by the American fleet. Throughout the Atlantic, the fleet landed mako sharks and fins (Nakano 1993). In the US and Canadian pelagic longline fisheries, shortfin mako is one of the most commonly caught sharks. The index of abundance in the commercial longline fishery off the Atlantic coast of US has shown a steady decline (Cramer 1996) and other reports on declines are now available (Baum et al. 2003, Baum et al., in prep, ICCAT 2005, Cortes et al. in press: see Population section for details). As for recreational fishing, Casey and Hoey (1985) stated that the recreational catch of shortfin makos along the US Atlantic coast and in the Gulf of Mexico in 1978 was 17,973 fish weighing some 1,223 t. Between 1987 and 1989, the catch was about 1000 t/year (Casey and Kohler 1992) taken by longline and gillnet in the Southwest Atlantic (see population section). Shortfin mako shark is a high value bycatch of pelagic longline fisheries on the Atlantic coast of Canada and therefore retained (Campana et al. 2005).
In 1989, Bonfil (1994) estimated that 5,932 shortfin makos were caught by Korean longliners in the (mainly equatorial) Atlantic and that 763 t of makos were landed in the Spanish swordfish fishery in the Mediterranean and Atlantic. Mejuto (1985) noted that 304-366 t of mako shark was landed by longliners operating from northern Spain in 1983-84. More recently, Shortfin Mako sharks have comprised about 7% (~2,500 t) of the total catch of the large Spanish pelagic longline swordfish fleet in the Atlantic (Mejuto et al. 2005). Munoz-Chapuli et al. (1994) estimated that some 4,500 makos/year are landed from a longline fishery based at Algeciras, southern Spain (given an average weight of 20 kg this would represent about 90 t). The landings of shortfin makos as bycatch from the swordfish fishery of the Azorean fleet also showed a decrease (Castro et al. 1999). Shortfin mako landings reported to ICCAT from Portuguese surface longline fisheries in the North Atlantic averaged about 698 t during 1993–1996 and 340 t for the period 1997–2002. Off Namibia, the large pelagic fisheries caught an estimated 123 t in 2001, 399 t in 2002 and 393 t in 2003 by means of pelagic longline. The 2001 catch is an underestimate as many boats grouped different shark species as “sharks” (MFMR catch data). Domingo (2002) records high catches of Shortfin Makos by the Uruguayan fleet in the early-mid 1980s (to a maximum of 144 t in 1984), followed by much lower catches (10–20 t/annum) in the 1990s. This does not necessarily reflect stock abundance because changes in the distribution and depth of fishing operations and rising mean temperature of water masses in the area had also occurred.
It has been estimated that in the early 1990s, the Spanish longline fleet caught approximately 750 t/y of Shortfin Mako sharks in the Atlantic Ocean and Mediterranean Sea (Bonfil 1994, Compagno 2001). The Brazilian longlining fleet based in Santos landed between 13.3 and 138.3 t annually between 1971 and 1990 (Costa et al. 1996, Compagno 2001). Despite increasing fishing effort during this period, the CPUE of Shortfin Makos has remained relatively stable with an initial slight decreasing trend followed by a slight increasing trend (Compagno 2001).
No complete data are available for the northeast Atlantic, but the species is taken as a bycatch of the pelagic fishery. The area around the Strait of Gibraltar is considered a nursery area for Central Atlantic Shortfin Makos and most specimens caught are juveniles. This area is heavily fished by the swordfish longline fishery off the western coast of Africa and Iberian peninsula. There is also evidence that shortfin makos are becoming increasingly targeted in the western Mediterranean. EU vessels fishing for small pelagic species off the western coast of Africa are also known to take significant elasmobranch bycatch, including Shortfin Makos in unknown numbers.
Northwest Atlantic and Western Central Atlantic
Canada and the USA have shark management plans (NMFS 1993; Joyce 1999). In the US, this species is included in the Highly Migratory Species Fishery Management Plan (FMP). The 1995 Fisheries Management Plan for pelagic sharks in Atlantic Canada established precautionary catch levels of 100 t for Shortfin Makos in the longline pelagic shark fishery. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) recently assessed shortfin mako in Canada as “threatened”. It has undergone a Recovery Potential Assessment and it is being determined whether the species will be placed on Sched 1 of the Species at Risk Act. License limitation, a ban on finning, restrictions on gear, area and seasons, by-catch limits and restrictions to recreational fishers permitting hook and release only were also implemented (Hurley 1998). Since 1993, shark fisheries in Atlantic and Gulf of Mexico waters in the US have been managed under the Fishery Management Plan for Sharks of the Atlantic Ocean. The plan set commercial quotas for 10 species of pelagic sharks at 580 t dressed weight annually, with recreational bag limits also applied.
Within the North Atlantic and Mediterranean this species has been identified as a high priority for management. Anonymous (2003) suggested that a collaborative stock assessment should be carried out in the future.
|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 (Atlantic subpopulation). In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 08 March 2014.|
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