Fish Facts » Blue Shark
The blue shark has a slender, sleek-looking body with a large eye and a long conical snout that is longer than the width of its mouth. It has extremely long, pointed pectoral fins, which generally are as long as the distance from its snout to posterior gill slit. The dorsal fin is moderate in size and set back where it is actually closer to the pelvic fin insertion than the pectoral insertion point. There is a slight keel on the caudal peduncle and the tail is narrowly lobed with a long ventral lobe. The blue shark's name comes from its distinct dark blue dorsal surface and bright blue sides. Its ventral surface is a well-defined, crisp white color. This contrast in colors is known as counter-shading and provides camouflage for the shark in the open ocean.
Being a pelagic species the blue shark's habitat consists of open ocean areas from the surface to 1,148 ft (350 meters) in depth. They prefer cooler water ranging from 44.6-60.8°F (7-16°C) but are known to have tolerances for water 69.8°F (21°C ) or greater. When in the tropics the blue shark tends to seek deeper waters with cooler temperatures. This is evident in the tropical Indian Ocean where the majority of blue sharks are found at depths of 262-722 ft (80-220m) where water temperatures range from 53.6-77°F (12-25°C). In the Pacific, at latitudes between 20°N and 50°N, they are known to migrate to higher latitudes during the summer and lower latitudes during the winter but their populations remain constant throughout the year between 20°N and 20°S latitude.
Small bony fishes, such as herring and sardines, and invertebrates, such as squid, cuttlefish and pelagic octopi, make up a majority of the blue shark's diet. They easily feed on certain species of squid that form large breeding aggregations, which allows the blue shark to leisurely collect its unsuspecting prey. Besides actively hunting for food, blue sharks are opportunistic feeders and have been known to feed from gill nets and scavenge dead marine mammals.
Recreationally blue sharks are considered a sport fish and larger individuals provide a challenge for fishermen using light tackle. Most commercially caught blue sharks are considered bycatch and it is estimated that 10 to 20 million are killed each year, possibly having a negative impact on world populations. The salmon, mackerel and pilchard fisheries are affected by blue shark predation on catch and entanglement in nets. Keeping blue shark meat is difficult since it ammoniates quickly so most blue sharks that are not released are fined. The fins are then sold to Asian markets and are used to make shark-fin soup. The blue shark is currently listed as "Near Threatened" by the World Conservation Union (IUCN). The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.
The largest blue shark on record measured 12.6 feet (383 cm) but they are rumored to get as large as 20 feet (609.6 cm). Males are believed to be mature at four to five years of age and at lengths between 6 feet (182 cm) and 9.2 feet (281 cm). Females mature slightly older ages ranging from five to six years and longer lengths from 7.3-10.6 feet (221-323cm). They are believed to live for more than 20 years.
Blue sharks are found world wide in temperate and tropical waters. They are a pelagic species that rarely comes near shore but have been known to frequent inshore areas around oceanic islands and locations where the continental shelf is narrow. In the Atlantic they can be found from New Foundland, Canada to Argentina and from Norway to South Africa, including the Mediterranean. They range from South Africa to Indonesia and from Japan to New Zealand in the Indian and western Pacific Oceans. In the eastern Pacific, blue sharks range from the Gulf of Alaska to Chile.
Florida Museum of Natural History
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