Habitat and Ecology
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).
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