The basking shark is the largest fish in British waters growing up to 9.8m long, its size being the most obvious distinguishing feature. Smaller specimens can be identified by the stout body, moon-shaped tail and the 5 long gill slits that run from the back behind the head to round under the throat. The gill arches carry a high number of gill rakers that act as a filter to catch the plankton upon which the fish feeds. The basking shark is slate grey to black dorsally, lighter ventrally, with light patches under the snout and on the belly. Filtered water is expelled through the greatly enlarged gill slits. Basking sharks generally live in open waters but migrate towards the shore in summer, when they can be seen 'basking' , i.e., swimming slowly at the surface with the mouth wide open with the snout and dorsal fin visible above water.

Description & Behavior

The basking shark, Cetorhinus maximus (Gunnerus, 1765), is recognized by its huge size, conical snout, sub-terminal mouth, extremely large gill slits, dark bristle-like gill rakers inside the gills (present most of the year), strong caudal keels and a lunate (curved) tail. The basking shark has numerous, small teeth. They are mottled gray/brown to slate-gray or black in color, sometimes with lighter patches on the dorsal side. The ventral side is paler, often with white patches under the snout and mouth or along the ventral side. Two albino basking sharks from the North Atlantic have been recorded. It is the second largest fish, only surpassed by the whale shark in size. The average size is 6.7-8.8 m. The largest measured specimen was 9.75 m, and a 9.14 m long individual was recorded that weighed 3,900 kg. There are unconfirmed reports of basking sharks up to 13.7 m long.

World Range & Habitat

Basking sharks, Cetorhinus maximus, are found in temperate waters of both the Pacific and Atlantic Oceans. They are usually observed by humans at or near the surface and have been sighted along almost every coastline bordering both the Atlantic and Pacific Oceans. Along the west coast of North America, they have been sighted from British Columbia to Baja California, usually in the winter and spring months. This trend is reversed in North Atlantic areas.

Feeding Behavior (Ecology)

The basking shark can open its cavernous mouth up to 1.2 m wide! This allows water to pass over the gill rakers, which strain small fishes and invertebrates out of the water. They are often seen feeding near the surface.

Life History

Basking sharks give birth to live young; the smallest juvenile recorded measured about 165 cm in length. Cetorhinus maximus females are believed to reach sexual maturity when they reach 4-4.9 m in length. Basking sharks have been observed breeding in the North Atlantic in May. The location of nursing grounds is unknown.

Comments

The basking shark has supported harpoon and net fisheries throughout the North Atlantic for centuries. It was fished for its liver oil, which was burned in lamps until replaced by petroleum products. A single shark yielded between 757-1,514 liters of oil.

Basking shark populations have been declining since the 1970's; they never fully recovered from the large scale commercial fisheries of the 1950's and remain over-fished in the North Atlantic.

Ref: http://marinebio.org/species.asp?id=193