Salmon Shark
The name of the salmon shark (Lamna ditropis) is derived from the Pacific salmon, which is a key component of its diet. This shark is closely related to the Porbeagle shark (Lamna nasus) and is occasionally confused with the Great White shark (Carcharodon carcharias).
Salmon shark anatomy and appearance
Salmon sharks typically grow to 2 to 2.5 meters in length and weigh around 220 kilograms, although there have been records of them growing up to 3 meters and weighing around 450 kilograms. They have stocky, spindle-shaped bodies with conical snouts that are shorter and blunter compared to the porbeagle sharks’. Salmon sharks have large gill slits, a strongly keeled caudal peduncle, and a crescent-shaped caudal fin. Lateral cusps – small bumps resembling tiny teeth – are present on either side of each tooth. Like the rest of its family (Lamnidae), the Salmon shark is endothermic. They possess retia mirabilia, which helps them retain heat produced by metabolism. This allows them to raise their body temperatures up to 15 to 16 degrees Celsius above their surroundings. Their ability to maintain different body temperatures gives them a greater vertical range in the water, which in turn, allows them to move freely through different water temperatures in pursuit of prey.
Salmon sharks are dark gray dorsally and laterally and white ventrally. The front, ventral side of their snouts also have a dark gray coloration. Unlike its close relative, the Porbeagle shark, the Salmon shark’s dorsal fin – including the rear tip – is completely dark. While the ventral side of juvenile Salmon sharks is pure white, adults have dark blotches that can help differentiate them from great white sharks.
Salmon shark habitat
Salmon sharks are migratory sharks, and their migrations depend highly on the availability of prey. Although salmon sharks are mainly pelagic, they are also known to travel near the coast. They can be found in subarctic and temperate waters in the North Pacific Ocean, and are most commonly found near Canada, Alaska, California, and Japan. This distinguishes Salmon sharks from Porbeagle sharks, since porbeagles are not found in the North Pacific. Salmon sharks prefer depths of at least 150 meters and cooler temperatures around 5-18 degrees Celsius.
Salmon shark populations are divided. The western North Pacific is predominantly inhabited by males, whereas females are more commonly seen in the eastern regions. The sharks' size also plays a role in determining their geographical distribution. Larger sharks tend to inhabit the northern areas, while smaller ones are typically found in the southern parts of the North Pacific.
Salmon shark diet
As their name suggests, Pacific salmon is a part of Salmon sharks’ diets, although they are not limited to this type of prey. As opportunistic feeders, they are known to eat a variety of other prey. Other bony fish like trout, herring, sardine, pollock, cod, lancetfish, and mackerel are also part of their diets. In addition to bony fish, Salmon sharks are also known to prey on squid. Salmon sharks use their speed and agility to hunt. After they find their prey, Salmon sharks use quick attacks to hunt them down. They have been known to hunt and feed alone and in groups of up to 30 or 40 individuals.
Salmon shark population
Salmon sharks have a lifespan of around 20 to 30 years. Males mature around 5 years of age (at 1.4 meters in length), while females mature around 8 to 12 years of age (at around 1.8 meters). Gestation is around 9 months. Common nursery grounds for pups include areas off the coast of California on the northeast side, and waters near Japan and southern regions in the northwest. Juveniles tend to stay in their nurseries until they are older. Salmon sharks are ovoviviparous, and give birth to live pups. Unlike most mammals, female Salmon sharks don’t have placental connections with the embryos. The embryos feed on unfertilized eggs – a process called oophagy. Litter size is around 2 to 5 pups, with 4 pups being the most common. Pups are typically 60 to 80 centimeters long at birth.
Salmon shark conservation
Salmon sharks are listed as least concern according to the IUCN (International Union for Conservation of Nature), although there are very few statistics from fisheries to indicate significant changes to their populations. Salmon sharks are commonly caught as bycatch, but are typically considered as inconveniences among fisheries due to the damage they are able to cause to fishing gear. There have also been numerous cases of juvenile Salmon sharks stranded along the coasts of the United States lately. Although there aren’t any regulations on fisheries internationally, in 1997, the Alaska Board of Fisheries stopped commercial fishing for Salmon sharks in Alaska and also set in place strict regulations on sport fishing.
Other interesting facts
While adult Salmon sharks are seldom targeted because of their significant size, juveniles face several predators. Apart from larger sharks like the Great White shark, potential predators may also include Orcas (Orcinus orca).