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North Atlantic Shortfin Mako Shark: History and Essential Fish Habitat

The information below provides additional information on the history, biology, and essential habitat of the Atlantic shortfin mako shark.

Shortfin Mako Shark (Isurus oxyrhincus)

The shortfin mako shark is a pelagic species found in warm and warm-temperate waters throughout all oceans. Heist et al . (1996) found considerable intraspecific genetic variation and significant partitioning of haplotypes between the North Atlantic and other regions; however, there was no evidence of multiple subspecies of shortfin mako, nor of any past genetic isolation between shortfin mako populations. It feeds on fast-moving fishes such as swordfish, tuna, and other sharks (Castro, 1983) as well as clupeids, needlefishes, crustaceans and cephalopods (Maia et al . 2007a). MacNeil et al., (2005) found evidence of a cephalopod to bluefish diet switch in the spring. It is considered one of the great game fishes of the world, and its flesh is considered among the best to eat. 

Reproductive Potential

Considerable variation exists in the descriptions of reproductive life history for shortfin mako sharks. Cailliet and Mollet (1997) estimated that a female mako shark matures at four to six years, has a two-year reproductive cycle, and a gestation period of approximately 12 months. According to Pratt and Casey (1983), females mature at about 7 years of age; however, Campana et al. (2002) using radiocarbon assays found that the estimate may be incorrect. Bishop et al. (2006) considered Campana et al. (2002) when estimating median age at maturity in New Zealand waters to be 19 to 21 years for females and 7 to 9 years for males. In Maia et al. (2007b), length at maturity for males is estimated at 180 cm fork length and female maturation is estimated to occur between 210-290 cm FL. Cailliet et al . (1983) estimated the von Bertalanffy parameters ( n = 44) for the shortfin as: L 4 = 3210 mm, K= .072, and t o = -3.75. Litter size ranges from 4 to 25, and size at birth is approximately 70 cm TL (Mollet et al. 2000). Gestation period was estimated at 15-18 months and the reproductive cycle at 3 years. Based on cohort analysis of fish in the eastern North Atlantic, average growth was determined as 61.1 cm/year for the first year and 40.6 cm/year for the second year (Maia et al., 2007b). There was a marked seasonality in growth, with average monthly rates of 5.0 cm/month in summer and 2.1 cm/month in winter. Lack of sex differences in cohort analysis for the first years of life is in accordance with previous studies reporting that male and female mako sharks grow at the same rate until they reach about 200 cm FL (Casey and Kohler, 1992; Campana et al ., 2005). Bishop et al. (2006) described rapid initial growth rates to approx. 39 cm fork length in the first year. Thereafter, males and females grow at similar, but slower rates until about age 7 years, after which the relative growth of males declines. Life span estimates vary and have been published as 11.5 years (Pratt and Casey, 1983), 25 years for females (Cailiet and Mollet, 1997), 29 and 28 years for males and females, respectively (Bishop et al,. 2006).

Very weak evidence of population structure throughout the Atlantic and Pacific Oceans was found in microsatellite analysis by Schrey and Hiest (2003). This same study indicated that integrating the results from microsatellite- and mitochondrial-based studies may provide evidence for gender-biased dispersal for the shortfin mako. The significant genetic structure detected in mtDNA data indicate that female shortfin makos may exhibit philopatry for parturition sites, and thus reproductive stocks of makos may exist in the presence of considerable male-mediated gene flow. Pregnant shortfin makos have only been captured between 20° and 30° N or S (Gilmore, 1993); however, there is no information about the area where mating occurs.

Impact of Fisheries

The shortfin mako is a common bycatch in tuna and swordfish fisheries. Because of their high market value, shortfin mako are usually the only sharks retained in some pelagic fleets with high shark bycatch rates. Off the northeast coast of North America, most of the catch consists of immature fish (Casey and Kohler, 1992). The index of abundance for shortfin makos in the commercial longline fishery off the Atlantic coast of the United States shows a steady decline (Cramer, 1996). The few indices available (ICES, 1995; Cramer, 1996; Holts et al., 1996) indicate substantial population decreases. The median size of shortfin mako sharks in the commercial catch off the eastern coast of Canada has declined since 1998, suggesting the loss of larger sharks (Campana et al., 2005). Because the species is commonly caught in widespread swordfish and tuna operations, it is reasonable to assume that similar decreases are occurring in areas for which there are limited data. 

Essential Fish Habitat

Note: At this time, insufficient data is available to differentiate essential fish habitat (EFH) by size classes, therefore, EFH is the same for all life stages.

Neonate/YOY, Juveniles, and Adults: EFH designation for all life stages have been combined and are considered the same. Localized areas in the central Gulf of Mexico and the Florida Keys. In the Atlantic, localized areas off of Florida, South Carolina, and Maine, and from Cape Lookout though southern New England. For more information on Atlantic HMS EFH, see the HMS Consolidated Fishery Management Plan, Amendment 1.

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The above information was taken from Amendment 1 to the Consolidated Atlantic Highly Migratory Species Fishery Management Plan. Citations can be found in Chapter 5 of that document.