|Male ocean phase pink salmon|
Pink salmon or humpback salmon, Oncorhynchus gorbuscha (from a Russian name for this species gorbúša, горбуша), is a species of anadromous fish in the salmon family. It is the smallest and most abundant of the Pacific salmon.
In the ocean, pink salmon are bright silver fish. After returning to their spawning streams, their coloring changes to pale grey on the back with yellowish-white belly (although some turn an overall dull green color). As with all salmon, in addition to the dorsal fin, they also have an adipose fin. The fish is characterized by a white mouth with black gums, no teeth on the tongue, large oval-shaped black spots on the back, a v-shaped tail, and an anal fin with 13-17 soft rays. During their spawning migration, males develop a pronounced humped back, hence their nickname "humpies". Pink salmon average 4.8 pounds (2.2 kg) in weight. The maximum recorded size was 30 inches (76 cm) and 15 pounds (6.8 kg).
Pink salmon in their native range have a strict two year life cycle, thus odd- and even-year populations do not interbreed. Adult pink salmon enter spawning streams from the ocean, usually returning to the water course, or race, where they originated. Spawning occurs between late June and mid-October, in coastal streams and some longer rivers, and in the intertidal zone or at the mouth of streams if hyporheic freshwater is available. Using her tail, the female digs a trough-shaped nest, called a redd (Scandinavian word for "nest"), in the gravel of the stream bed, wherein she deposits her eggs. As she expels the eggs, she is approached by one or more males, which fertilize them as they fall into the redd. Subsequently, the female covers the newly deposited zygotes, again with thrusts of her tail, against the gravel at the top of the redd. The female lays from 1000 to 2000 eggs in several clutches within the redd, often fertilized by different males. Females guard their redds until death, which comes within days of spawning. In dense populations, a major source of mortality for embryos is superposition of redds by later-spawning fish. The eggs hatch from December to February, depending on water temperature, and the juveniles emerge from the gravel during March and April and quickly migrate downstream to estuaries, at about one-quarter gram in weight. The fish achieve sexual maturity in their second year of life. They return to freshwater in the summer or autumn as two-year-old adults. Pink and chum salmon sometimes interbreed in nature to form the hybrid known as the miko salmon; the hybrids are reproductively sterile.
The sex that cares for the young depends on which has the most to gain from successful parenting, or in terms of fitness, which sex’s fitness will benefit the most from caring for the young. The overall fitness associated with raising the young is determined not only by the propagation of one’s genes, but also by incurring the least loss in terms of energy and effort for the caretaker. The benefits for each of the sexes are the same due to the greater chance of genes being passed down to future generations, but the costs for each sex are different.
Species can either be semelparous, meaning they have a single reproductive cycle before dying, or iteroparous, meaning they have multiple reproductive episodes throughout their lifetime. In semelparous species, females will guard their redds from other females. In iteroparous species, females will leave their redds quickly after spawning. Pink salmon are part of the genus Oncorhynchus, or Pacific salmon. In the genus Oncorhynchus, females are semelparous, whereas males are iteroparous. Therefore for female pink salmon, it benefits them to care for their eggs, because no more opportunities to breed exist in the future. Thus, it is in the female’s best interest to make sure all of the children thrive successfully. However, there exists a cost for a male pink salmon who chooses to engage in parental care; males would lose out on more chances to mate, and thus, miss opportunities to pass on their genes. Because of these associated costs and benefits, female pink salmon have evolved to protect their eggs until they die, whereas males will pursue other opportunities to mate.
Pink salmon are coldwater fish with a preferred temperature range of 5.6 to 14.6°C, an optimal temperature of 10.1°C, and an upper incipient lethal temperature of 25.8°C. The species is native to Pacific and Arctic coastal waters from the Sacramento River in northern California to the Mackenzie River in Canada; and in the west from the Lena River in Siberia to Korea. Populations in Asia occur as far south as Hondo Island in Japan. Pink salmon were introduced into the Great Lakes and in Iran.
The commercial harvest of pink salmon is a mainstay of fisheries of both the eastern and western North Pacific; over 100 million have been taken in recent annual harvests in Alaska alone. More than 20 million harvested pink salmon are produced by fishery-enhancement hatcheries, particularly in the northern Gulf of Alaska. Pink salmon are not grown in significant numbers in fish farms. The fish are often canned, smoked or salted. Pink salmon roe is also produced commercially for caviar, a particularly valuable product in Asia.
Beginning in the late 19th century, fish traps were used to supply fish for commercial canning and salting. The industry expanded steadily until 1920. During the 1940s and 1950s, pink salmon populations declined drastically. Fish traps were prohibited in Alaska in 1959. Now, most pink salmon are taken with purse seines, drift nets or gillnets. Populations and harvests increased rapidly after the mid-1970s and have been at record high numbers since the 1980s.
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- Oncorhynchus gorbuscha NatureServe conservation status
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