Latin name

Lamnа ditropis

Other names

Lamnа ditropis

Identification

They have a thick spindle-shaped body, a short conical snout (the distance from the tip of the snout to the eye is about 40% of the distance from the eye to the first gill slit) and long gill slits that extend over the surface of the head. The distance from the tip of the snout to the mouth is 4.5% to 7.6% of body length (4.5% to 5% in adults). The salmon shark has a total of 170 vertebrae, with 103 vertebrae in the backbone. 

Salmon sharks are endothermic and are able to maintain a body temperature higher than that of their environment. It is a dense structure in the form of a tangle of veins and arteries that runs along the sides of the torso. It allows them to retain heat by warming cold arterial blood with venous blood warmed by muscle activity. This structure allows these sharks to hunt effectively over a wide range of temperatures. 

Teeth

The teeth are fairly large, sharp and the edges are smooth.

Features of fish fins

First dorsal fin large, triangular in shape, apex rounded, base posterior to the base of the pectoral fins. The tip of the first dorsal fin is free. Pectoral fins large, almost as long as the first dorsal fin. The pelvic, second dorsal and anal fins are small. The anal and second dorsal fins are displaced towards the tail. There are strong keels on the caudal peduncle. There are short secondary keels on either side of the caudal peduncle at the base of the caudal fin. The caudal fin is crescent-shaped. The lower lobe is almost as large as the upper lobe.

Fish colouring

Dorsal surface of body bluish-grey or bluish-black, space under snout, lower jaw and belly whitish, covered with grey spots in individuals over 1.5 m long.

Distribution

Occupies the North Pacific off Japan (including the Sea of Japan), Korea, the Pacific waters of Russia (including the Sea of Okhotsk), the United States and possibly Mexico. 

Habitat

They are found both offshore and in the open sea. They prefer the northern and cooler waters of temperate latitudes. They are usually found at depths of up to 152 metres. Water temperatures in the range of these sharks vary from 3.5°C to 22.5°C and salinity ranges from 31.5-34.25 ‰. 

Size

Adults are about 2-2.6 m long and weigh up to 265 kg. Females are slightly larger than males. The maximum recorded length of the salmon shark is 3.05 m and its weight is 454 kg.

Behavior

These sharks are divided by sex and size. Males predominate in the western Pacific and females in the eastern Pacific. Salmon sharks are usually solitary, but can gather in packs of 30-40 when hunting at night. Adult sharks, unlike juveniles, migrate and travel further north. In the western Pacific, large sharks migrate in winter from the coast of Japan, where they breed, and move north with warming waters to the Sea of Okhotsk and the western Bering Sea. They return to Japanese waters in autumn or early winter (a one-way distance of 3,220 km). In the eastern Pacific, females migrate south to the coasts of Oregon and California, USA, where they give birth to their young. 

Food and feeding habits

At the top of the food pyramid, Salmon Sharks are well-adapted predators that prey on a variety of demersal and pelagic fish. Their diet consists of Rainbow Trout, Oncorhynchus, Clupea and Sardine, Saithe, Pacific Cod, Microgadus Tomcod, Cutlass Fish, Daggertooth, Pacific Saury, Lanternfish, Scomber, Cyclopterus, Cottus, probably Scorpaena, Sablefish and Atka Mackerel. They also prey on spurdog and some pelagic squid, and are attracted to fish caught as bycatch and discarded by shrimp trawlers.

Reproduction

Reproduces by placenta-free live birth with oophagy (intrauterine cannibalism). There are 2 to 5 newborns in a litter, 80-87 cm long (other reports say 50-55 cm). The gestation period is probably about 9 months. The length of the complete reproductive cycle is not known. Mating occurs in late summer and early autumn, and young are born in spring. Mating sites and natural nurseries are located offshore in the western Pacific Ocean between 156°W and 180°W near the southern Kuril Islands and in the Sea of Okhotsk, where immature sharks of 110-120 cm in length are found. 

Development

In the first year of life, juveniles reach a length of 120-140 cm, which accounts for 75% of the growth. In the following years, growth slows down and does not exceed 10-15 cm per year by the age of 4. Females then begin to grow faster than males. Males reach sexual maturity at a length of about 182 cm, corresponding to an age of 5 years, and females at a length of 221 cm, corresponding to an age of 8-10 years. Females in the eastern Pacific live at least 20 years, and males 27 years.

Fishing

The species is of little commercial interest. It is caught by sport fishermen off the coast of Japan and Alaska.

Relationship with a person

Considered potentially dangerous to humans due to their large size. No attacks on humans have been officially recorded. Salmon shark meat is eaten in Japan.