Aquatic Species at Risk - Shortfin Mako (Atlantic population)
Species - Details
Last COSEWIC Assessment : April 2006
Last COSEWIC Designation: Threatened .
Region: Atlantic Ocean
About the Shortfin Mako
The shortfin mako (Isurus oxyrinchus) is one of five species in the family commonly known as mackerel sharks which includes the great white shark and basking shark. The mako shark is described as spindle shaped, deep blue to purple above and white below, with a conical head, sharply pointed snout and crescent shaped caudal fin. The u-shaped mouth has large sharp teeth that protrude outside of the mouth even when closed. It can reach a maximum length of over 4 m.
Shortfin mako are found around the world from temperate to tropical waters. In the northwest Atlantic they have been found both inshore and offshore, from Bermuda to the waters east of Newfoundland. In Canadian waters where they are considered at the edge of their range, they have been recorded from the Grand Banks off Newfoundland, along the Scotian Shelf and down to Georges Bank.
Tagging studies indicate that shortfin makos are highly migratory with distribution apparently dependent on water temperatures which they prefer between 17 and 22℃. They migrate to the Atlantic coast of Canada generally in the late summer and fall where they are usually associated with the warm waters of the Gulf Stream.
They are extremely adaptable and able to withstand significant changes in temperature as well as changes in food availability over its wide range. Shortfin mako feed primarily on other fishes including tuna, mackerel, bluefish and swordfish, but may also eat marine mammals.
Unlike most other sharks, mackerel sharks are able to regulate their body temperatures which the shortfin mako, in particular, maintains at 1 to 10o C above its surrounding water temperature. This allows the shortfin mako (one of the fastest sharks in the world) to sustain its high swimming speeds when migrating through colder, deeper waters.
Females mature at lengths of 2.7 to 3 m (corresponding to an age of about 17 years) and give birth to a litter size of 4 to 25 pups after a gestation period of approximately 15 to 18 months. Pups are approximately 70 cm at birth. Although males mature slightly at a slightly smaller length of 2 to 2.2 m, their age of maturity is much lower at 7 to 9 years. The minimum lifespan has been estimated at 24 years with a maximum life expectancy of up to 45 years.
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has identified fishing and pelagic longlining in particular, as being the most significant threat to the shortfin mako. There are no fishery-independent abundance estimates for this species and the largely unmonitored longlining effort in international waters increases the uncertainty in abundance trends
There is no directed fishery for shortfin mako in Atlantic Canada, but it is caught as bycatch in other pelagic fisheries for swordfish, shark and tuna. Studies of bycatch in Atlantic Canadian waters indicate that shortfin mako make up 2 to 3% of the total weight of the pelagic longline fishery for swordfish. Because the meat is highly prized, this bycatch is rarely discarded at sea.
International studies based on American and Japanese longline data indicate catch rate declines of 40 to 50 % for shortfin mako. While these declines have not been observed in Atlantic Canadian waters, preliminary studies do indicate a recent decline in the abundance of larger individuals.
Shortfin makos are also sought after by sport fishers who value them for their “fighting” ability as well as their edible flesh.
Shortfin makos are managed under the Canadian Atlantic Pelagic Shark Integrated Fisheries Management Plan which allows for an unrestricted bycatch along with 100% dockside monitoring. The recreational shark fishery is “catch and release” only except in the case of a fishing derby when carcasses may be kept for scientific purposes. Also, the practise of “finning”, (removing and keeping the fins to sell while discarding the carcasses) has been prohibited in all Canadian waters since 1994.
COSEWIC 2006. COSEWIC assessment and status report on the shortfin mako (Atlantic population) Isurus oxyrinchus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 24 pp. (www.sararegistry.gc.ca/).
DFO, 2002. Canadian Atlantic Pelagic Shark Management Plan 2002-2007.
Canadian Shark Research Laboratory website: http://www.marinebiodiversity.ca/shark/english/mako.htm.
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