Shortfin mako shark

Isurus oxyrinchus

Description

The shortfin mako shark is a sleek spindle shaped shark with a long conical snout. This shark has short pectoral fins and a crescent shaped caudal fin. There is a distinct caudal keel on the caudal base. Its second dorsal fin is much smaller than the first. The teeth are slender and slightly curved with no lateral cusps, and are visible even when the mouth is closed giving it a fearsome appearance. There is marked countershading on this shark: dorsally it is a metallic indigo blue while ventrally it is white.

Range

The shortfin mako is found worldwide. In the western Atlantic it can be found from Argentina and the Gulf of Mexico to Browns Bank, along the continental shelf of Nova Scotia and even into the Gulf of St. Lawrence. In Canadian waters these sharks are not abundant as they prefer warm waters, but neither are they rare. Shortfin makos are often found in the same waters as swordfish, as they are a source of food, and both fish prefer similar environmental conditions. In some years, warm water conditions can bring them closer to shore; in 2002 for example, several makos were caught during blue shark fishing derbies and as part of recreational shark fishing trips about 10 miles outside of Halifax Harbour. However, no makos have been observed within a mile of shore.

Habitat

Shortfin mako sharks live in tropical and temperate offshore waters. They are a pelagic species that occur from the surface down to depths of 500 meters (1600 feet). This shark is seldom found in waters colder than 16 degrees Celsius. It is typically found in waters between 17 and 22 degrees Celsius.

Life History

The shortfin mako can grow to lengths of 3.9 meters (13 feet). There is still some uncertainty about its lifespan, but it is known to reach ages of at least 32 years.

As one of the fastest sharks in the ocean, this powerful shark can attain burst swimming speeds of up to 68 km/h (42 mph) and can leap clear of the water to heights of up to 6 meters (20 feet). Like porbeagle sharks, they are able to conserve metabolic heat and maintain their bodies 7-10 C higher then their surroundings. They routinely jump 2-3 times after being hooked to try to free themselves. This is a spectacular sight to witness (see picture below) but can be somewhat dangerous as the possibility exists that they may jump right in the boat. These qualities have made this species a sought after sport fish in some parts of its range. It is a highly migratory species with evidence of crossing the Atlantic to european waters through tagging experiments.

Diet

The shortfin mako feeds mainly upon squid and bony fishes including mackerels, tunas, bonitos and swordfish, but may also eat other sharks, porpoises and sea turtles. Marine mammals other than porpoises are consumed on occasion as well.

Reproduction

Female shortfin makos usually become sexually mature at a length of about 2.75 meters fork length (17-19 years), while males mature at about 1.85 metres fork length (7-9 years). Developing embryos feed on unfertilized eggs in the uterus during the gestation period of 15-18 months. The 4-25 surviving young (average of 11) are born live in the late winter and early spring at a length of about 70 œ 77 cm, but have no placental connection during development (ovoviviparity). It is believed that females may rest for 18 months after birth before the next batch of eggs are fertilized.

Interaction with People

The mako shark has been the subject of considerable research in our laboratory. This shark is an important species to man in both the commercial and recreational fisheries. A recent stock assessment (CSAS resdocs - 2004/094) is available. Its meat is of high quality and it is prized as one of the greatest game fishes in the world. It is rarely encountered by swimmers or divers due to its oceanic nature and should be treated with respect and caution. The mako has been known to attack boats on occasion but most of these attacks are usually linked to being hooked by game fishers and are considered abnormal behavior.

The mako population spans the entire North Atlantic Ocean. Although only 2-3% of the mako catch comes from Canadian waters, COSEWIC has recommended that the population be listed as Threatened in Canadian waters. DFO carried out a Research Document (CSAS resdocs - 2006/091) for which is also available.

Distinguishing Characteristics

• Teeth are visible even when the mouth is closed
• Teeth are long and slender with smooth-edged cusps
• Distinct countershading, dorsally blue and ventrally white
• Moderately short pectoral fins
• Underside of the snout is white
• Lunate tail and caudal keel