Salmon shark
Encyclopedia
The salmon shark, Lamna ditropis, is a species of shark
occurring in the north Pacific ocean. As an apex predator
, the salmon shark feeds on salmon
, and also on squid
, sablefish
, and herring
. Salmon shark are remarkable for their ability to maintain body temperature, known as homeothermy, and an as-yet unexplained variability in the sex ratio
between the eastern north Pacific and western north Pacific.
. The eyes are positioned well-forward enabling binocular vision to accurately locate prey.
Salmon shark generally grow to between 200 and 260 cm (79–103 in) in length and weigh up to 220 kg
(485 lbs). Males appear to reach a maximum size which is slightly smaller than females. Unconfirmed reports exist of salmon shark reaching as much as 4.3 m (14.2 ft) however the largest confirmed reports indicate a maximum total length of approximately 3 m (10 ft). The maximum reported weight of this heavily-built shark is over 450 kg (992 lbs).
shark species, salmon sharks are oophagous
, with embryo
s feeding on the ova produced by the mother.
Females reach sexual maturity at 8 to 10 years, while males generally mature by age 5. Reproduction timing is not well understood, however it is believed to be on a two year cycle with mating occurring in the late summer or early fall. Gestation
is approximately 9 months. Some reports indicate that the sex ratio at birth may be 2.2 males per female, however the prevalence of this is not known.
, Latin for "wonderful nets." Blood moving toward extremities flows near colder returning blood, resulting in heat transfer. The returning blood is warmed, keeping the core of the animal heated. This ability is believed to help the salmon shark exploit prey in a wider range of water temperatures.
Salmon shark occur in the northern Pacific Ocean, in both coastal waters and in the open ocean. Animals are believed to range as far south as the Sea of Japan
and as far north as 65 degrees north
in Alaska
and in particular in Prince William Sound
during the annual salmon run. Individuals have been observed diving as deep as 668 m, however they are believed to spend most of their time in epipelagic waters.
, or if the segregation occurs as part of salmon shark growth and development.
in commercial salmon
gillnet fisheries where they are usually discarded. Commercial fisheries regard salmon sharks as nuisances since they can damage fishing gear and consume portions of the commercial catch. There are some reports of fishermen deliberately injuring salmon sharks.
Sport fishermen fish for salmon sharks in Alaska. Alaskan fishing regulations limit the catch of salmon shark to two sharks per person per year.
The flesh of the fish is utilized for human consumption, and in the Japan
ese city of Kesennuma, Miyagi
, the heart is considered a delicacy for use in sashimi
.
Although salmon sharks are thought to be capable of injuring humans, there are few if any attacks on humans. There are, however, reports of divers encountering salmon sharks as well as salmon sharks bumping fishing vessels. These reports, however, may need positive identification of the shark species involved.
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
occurring in the north Pacific ocean. As an apex predator
Apex predator
Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
, the salmon shark feeds on salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
, and also on squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, sablefish
Sablefish
The sablefish, Anoplopoma fimbria, is one of two members of the fish family Anoplopomatidae and the only species in the Anoplopoma genus...
, and herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
. Salmon shark are remarkable for their ability to maintain body temperature, known as homeothermy, and an as-yet unexplained variability in the sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
between the eastern north Pacific and western north Pacific.
Biology
Adult salmon sharks are medium grey to black over most of the body, with a white underside with darker blotches. Juveniles are similar in appearance but generally lack blotches. The snout is short and cone-shaped, and the overall appearance is similar to a small great white sharkGreat white shark
The great white shark, scientific name Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. It is known for its size, with the largest individuals known to have approached...
. The eyes are positioned well-forward enabling binocular vision to accurately locate prey.
Salmon shark generally grow to between 200 and 260 cm (79–103 in) in length and weigh up to 220 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
(485 lbs). Males appear to reach a maximum size which is slightly smaller than females. Unconfirmed reports exist of salmon shark reaching as much as 4.3 m (14.2 ft) however the largest confirmed reports indicate a maximum total length of approximately 3 m (10 ft). The maximum reported weight of this heavily-built shark is over 450 kg (992 lbs).
Reproduction
Salmon shark are ovoviviparous, with a litter size of 2 to 6 pups. As with other LamniformesLamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...
shark species, salmon sharks are oophagous
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....
, with embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s feeding on the ova produced by the mother.
Females reach sexual maturity at 8 to 10 years, while males generally mature by age 5. Reproduction timing is not well understood, however it is believed to be on a two year cycle with mating occurring in the late summer or early fall. Gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
is approximately 9 months. Some reports indicate that the sex ratio at birth may be 2.2 males per female, however the prevalence of this is not known.
Homeothermy
As with only a few other species of fish, salmon shark have the ability to regulate their body temperature. This is accomplished by vascular counter-current heat exchangers, known as retia mirabiliaRete mirabile
A rete mirabile is a complex of arteries and veins lying very close to each other, found in some vertebrates. The rete mirabile utilizes countercurrent blood flow within the net...
, Latin for "wonderful nets." Blood moving toward extremities flows near colder returning blood, resulting in heat transfer. The returning blood is warmed, keeping the core of the animal heated. This ability is believed to help the salmon shark exploit prey in a wider range of water temperatures.
Range and distribution
It is common in continental offshore waters but range inshore to just off beaches. They occur singly or in schools or feeding aggregations of several individuals.Salmon shark occur in the northern Pacific Ocean, in both coastal waters and in the open ocean. Animals are believed to range as far south as the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
and as far north as 65 degrees north
65th parallel north
The 65th parallel north is a circle of latitude that is 65 degrees north of the Earth's equatorial plane. It crosses the Atlantic Ocean, Europe, Asia and North America....
in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and in particular in Prince William Sound
Prince William Sound
Prince William Sound is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the Trans-Alaska Pipeline System...
during the annual salmon run. Individuals have been observed diving as deep as 668 m, however they are believed to spend most of their time in epipelagic waters.
Regional differences
Age and sex composition differences have been observed between populations in the eastern and western North Pacific. Eastern populations are dominated by females, while the western populations are predominately male. It is not known if these distinctions stem from genetically distinct stocksFish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...
, or if the segregation occurs as part of salmon shark growth and development.
Human interactions
There is no current commercial fishery for salmon shark, however, they are occasionally caught as bycatchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
in commercial salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
gillnet fisheries where they are usually discarded. Commercial fisheries regard salmon sharks as nuisances since they can damage fishing gear and consume portions of the commercial catch. There are some reports of fishermen deliberately injuring salmon sharks.
Sport fishermen fish for salmon sharks in Alaska. Alaskan fishing regulations limit the catch of salmon shark to two sharks per person per year.
The flesh of the fish is utilized for human consumption, and in the Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese city of Kesennuma, Miyagi
Kesennuma, Miyagi
is a city located in the extreme northeast of Miyagi Prefecture, Japan, founded on June 1, 1953. It wraps around the western part of Kesennuma Bay, and also includes the island of Ōshima...
, the heart is considered a delicacy for use in sashimi
Sashimi
Sashimi is a Japanese delicacy. It consists of very fresh raw meat, most commonly fish, sliced into thin pieces.-Origin:The word sashimi means "pierced body", i.e...
.
Although salmon sharks are thought to be capable of injuring humans, there are few if any attacks on humans. There are, however, reports of divers encountering salmon sharks as well as salmon sharks bumping fishing vessels. These reports, however, may need positive identification of the shark species involved.
External links
- Salmon shark fact sheet
- Florida Museum of Natural History, information about salmon sharks
- TOPP, Tagging of Pacific Predators, a research group that tags salmon sharks to learn more about their habits.