Kitefin shark

Description

The kitefin shark or seal shark (Dalatias licha) is a species of dogfish shark in the family Dalatiidae,and the only species in its genus.It is found sporadically around the world,usually close to the sea floor at depths of 200–600 m (660–1,970 ft).With a sizable oil-filled liver to maintain neutral buoyancy,this shark is able to cruise slowly through the water while expending little energy.The kitefin shark has a slender body with a very short,blunt snout,large eyes,and thick lips.Its teeth are highly differentiated between the upper and lower jaws,with the upper teeth small and narrow and the lower teeth large,triangular,and serrated.Its typical length is 1.0–1.4 m (3.3–4.6 ft).Armed with large teeth and a strong bite,the kitefin shark is a powerful,solitary predator that takes many different types of prey,ranging from bony fishes,sharks and rays,to cephalopods,crustaceans,polychaete worms,siphonophores,and possibly carrion.It also takes bites out of animals larger than itself,similar to its smaller relative,the cookiecutter shark (Isistius brasiliensis).This shark is aplacental viviparous and gives birth to 10–14 young.The kitefin shark is fished commercially for its meat,skin,and liver oil,primarily by Portugal and Japan.A fishery targeting this species existed off the Azores from the 1970s to the 1990s,but collapsed due to overfishing and falling liver oil prices;the rapid depletion of the Azores stock is often cited as an example of the susceptibility of deep-sea sharks to human exploitation.The low reproductive rate of this species renders it susceptible to overfishing and,coupled with known population declines,has led it to be assessed as Near Threatened by the International Union for Conservation of Nature (IUCN).The kitefin shark has a moderately elongated body with a very short,rounded snout.The eyes and spiracles are large.The lips are thick with pleats or fringes,though are not modified to be suctorial.There are 16–21 tooth rows in the upper jaw and 17–20 tooth rows in the lower jaw.The upper teeth are small and spike-shaped,curving slightly towards the corners of the mouth.The lower teeth are very large,knife-shaped,and serrated,with their bases interlocking to form a continuous cutting surface.The first dorsal fin is slightly smaller and shorter-based than the second,and neither has spines.The first dorsal fin originates behind the free rear tip of the pectoral fins,while the second originates above the middle of the pelvic fin bases.The pectoral fins are short and rounded.The caudal fin has a prominent upper lobe with a well-developed notch near the tip,and a barely present lower lobe.The form and arrangement of the fins is similar to the Portuguese dogfish (Centroscymnus coelolepis),from which this species can be distinguished by the lack of fin spines.The dermal denticles are small and flat,with a single horizontal ridge ending in a point.