The blue shark is one of the most easily recognized sharks. It has a distinct coloration, a deep indigo blue from above and a vibrant blue on its sides, changing to white underneath. The large pectoral fins are also easy to spot as they are as long as the distance between the tip of the snout to the last gill slit. The blue shark is a long slender shark, reaching 13 feet in length. It is likely the most prolific of the large shark species as it is abundant throughout its range. The blue shark has a weak keel on the caudal peduncle and the upper lobe of the caudal fin is larger than the lower. The teeth on both the lower and upper jaw have triangular cusps with smooth or finely serrated edges.

Diet
The diet of this shark includes many types of fish and squid, and may sometimes eat seals. Although flatfishes make up part of the diet, blue sharks predominantly eat pelagic fishes such as herring, silver hake, white hake, red hake, cod, haddock, pollock, mackerel, butterfish , sea raven, tuna and swordfish. Fish caught on longlines during fishing are often attacked and consumed by blue sharks, who in turn often become ensnared in the fishing gear.

Reproduction
The blue shark is a viviparous species, nourishing the young in the uterus and giving birth to live pups. The new-born pups measure 16 to 20 inches in length and litters usually consist of between 25 to 50 individuals. Litters of up to 135 pups have been reported. Females reach sexual maturity at a size of 7 to 11 feet, while for males it is achieved at lengths of 6 to 9 feet. After copulation the females may retain and nourish the spermatozoa in the oviducal gland for months or even years while she awaits ovulation. Once the eggs have been fertilized there is a gestation period of between 9 and 12 months.

Habitat
In temperate waters the blue shark is a wide ranging pelagic species occurring near the surface. In tropical waters the blue shark is more commonly found in deeper waters as it prefers temperatures between 7 and 16 degrees Celsius.

The blue shark occurs in the Atlantic, Pacific and Indian Oceans in both inshore and offshore waters. This wide ranging species is found from 50º N latitude to 50ºS latitude. In the western Atlantic it can be found from Newfoundland and the Gulf of St. Lawrence to Argentina. In Canadian waters the blue shark has been found in southeastern Newfoundland, the Grand Banks, the Gulf of St. Lawrence, the Scotian Shelf and the Bay of Fundy.

Shortfin Mako Shark (Isurus oxyrinchus)

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 (tail) fin. There is a distinct caudal keel on the caudal base. Its second dorsal fin is much smaller than the first. The teeth are are slender and slightly curved with no lateral cusps, and are visible even when the mouth is closed. There is marked countershading on this shark: dorsally it is a metallic indigo blue while ventrally it is white.

The shortfin mako can grow to lengths of 13 feet. There is still some uncertainty about its life-span, but it is suspected to reach ages of between 11-23 years.

As one of the fastest sharks in the ocean, this powerful shark can attain burst swimming speeds of up to 22 mph and can leap clear of the water to heights of up to 20 feet. These qualities have made this species a sought after sport fish.

Diet
The shortfin mako feeds mainly upon bony fishes including mackerels, tunas, bonitos and swordfish, but may also eat other sharks, porpoises and sea turtles.

Reproduction
Female shortfin makos usually become sexually mature at a length of 3 meters. Developing embryos feed on unfertilized eggs in the uterus during the gestation period of 15-18 months. The 4-18 surviving young are born live in the late winter and early spring at a length of about 70 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.

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 150 meters (490 feet). This shark is seldom found in waters colder than 16 degrees Celsius.