Pink salmon exhibit fascinating physical characteristics throughout their lifecycle. In the ocean, these fish appear as bright silver specimens. However, upon returning to their spawning streams, their coloring transforms into a pale grey on the back, accompanied by a yellowish-white belly. Some individuals may even exhibit an overall dull green coloration. Notably, pink salmon possess an adipose fin in addition to the dorsal fin, which is a distinguishing feature of all salmon species. They have a white mouth with black gums, lack teeth on the tongue, and sport large oval-shaped black spots on their backs. The fish display a v-shaped tail and an anal fin containing 13-17 soft rays. During their spawning migration, males develop a pronounced humped back, earning them the nickname "humpies." Pink salmon typically weigh around 4.8 pounds (2.2 kg) on average, with the maximum recorded size reaching 30 inches (76 cm) and 15 pounds (6.8 kg).
The native range of pink salmon encompasses the Pacific and Arctic coastal waters and rivers. These fish can be found from the Sacramento River in northern California to the Mackenzie River in Canada. In the western region, their habitat extends from the Lena River in Siberia to Korea and Honshu in Japan. Pink salmon spawn in various locations, ranging from the Arctic's Mackenzie River to tributaries of Puget Sound, Washington. Notably, there have been sightings of pink salmon in the San Lorenzo River near Santa Cruz, California, in 1915, as well as the Sacramento River in northern California during the 1950s. In recent years, they have even been recorded in the Salinas River, marking the southernmost extent of spawning for this species. Additionally, a small population of pink salmon was discovered in Lagunitas Creek, located about 25 miles (40 km) north of San Francisco, California.
Apart from their native range, pink salmon have been introduced into the Great Lakes of North America, where self-sustaining populations now exist. They have also been periodically introduced to rivers in the White Sea and Barents Sea basins in Russia since 1956. Consequently, stray fish from these rivers have been observed ascending rivers in Norway, Sweden, Ireland, Great Britain, and Iceland. Notably, self-sustaining populations have been observed in Norway. In 2017, Scotland witnessed an unusual increase in the number of pink salmon caught in rivers, with documented instances of spawning. More recently, in 2021, pink salmon were reported to have invaded Akerselva in downtown Oslo, the capital of Norway.
Habitat
Pink salmon thrive in coldwater environments, with a preferred temperature range of 5.6 to 14.6 °C. The optimal temperature for their survival is around 10.1 °C, while temperatures exceeding 25.8 °C can be lethal.
Reproduction
Pink salmon exhibit a strict two-year life cycle within their native range, with odd and even-year populations refraining from interbreeding. In the state of Washington, pink salmon runs primarily occur during odd years. Adult pink salmon return to their spawning streams from the ocean, often selecting the stream where they originated. Spawning typically takes place between late June and mid-October in coastal streams, longer rivers, or at the intertidal zone and mouth of streams if hyporheic freshwater is available.
During the spawning process, the female uses her tail to create a trough-shaped nest called a "redd" in the gravel of the stream bed. She deposits her eggs within the redd, and as the eggs are expelled, one or more males approach to fertilize them. The female then covers the newly deposited zygotes with further tail movements against the gravel at the top of the redd. A female pink salmon can lay anywhere from 1,000 to 2,000 eggs in several clutches within the redd, with different males fertilizing each clutch. The females guard their redds until death, which typically occurs within days of spawning. In densely populated areas, the superposition of redds by later-spawning fish can lead to a high mortality rate for the developing embryos.
The eggs hatch between December and February, depending on water temperature, and the juveniles emerge from the gravel during March and April. At this stage, they weigh approximately one-quarter gram and swiftly migrate downstream to estuaries. The fish reach sexual maturity in their second year of life and return to freshwater during the summer or autumn as two-year-old adults. It's worth noting that pink and chum salmon occasionally interbreed in nature, resulting in a hybrid known as the miko salmon; however, these hybrids are sterile.
Diet
Juvenile pink salmon primarily feed on invertebrates and zooplankton during their freshwater stage. Once they transition to the ocean, their diet expands to include a variety of plankton, invertebrates, and small fish. However, when the adult salmon return to freshwater to spawn, they cease feeding altogether.
Pink salmon play an essential role in the food webs of their ecosystems. Throughout their life cycle, they serve as a food source for various animals. When the salmon are in their egg or fry stages within freshwater ecosystems, they are preyed upon by small fish, birds, and mammals. In the ocean, larger fish, seabirds, and marine mammals feed on pink salmon.
Notably, the eggs and carcasses of spawned salmon adults provide substantial nutrient subsidies to freshwater food webs. In subarctic Norwegian rivers where pink salmon have expanded, native salmonids consume their eggs. Higher numbers of pink salmon eggs in the Keogh River in Canada have been shown to reduce competition among other fish species reliant on this food source. Bears, known to feed on migrating adult salmon, selectively target those that have not yet spawned, as they are more nutritious. These bears often transport the caught salmon away from water bodies into riparian areas and forests. Consequently, the nutrients from the salmon carcasses enrich the surrounding plants and trees. When the carcasses of successfully spawning pink salmon decompose, they attract aquatic invertebrates, further contributing to the nutrient cycle in stream habitats. The overall increase in resource subsidies can enhance the growth of other salmonid species within the streams.
The conservation status of pink salmon varies across their range. According to NatureServe, they are listed as critically imperiled in California, imperiled in Washington, and considered secure in Alaska and British Columbia. Notably, no pink salmon Evolutionary Significant Units are currently listed under the Endangered Species Act.
Pink salmon are a vital resource for commercial fisheries in both the eastern and western North Pacific regions. In 2010, the total harvest of pink salmon reached approximately 260 million fish, equivalent to 400,000 tonnes. Russian fisheries accounted for 140 million fish, while Alaska in the USA contributed 107 million fish. Pink salmon represents a substantial portion, approximately 69%, of the total Russian salmon fisheries. Coastal set net traps are the primary method employed for harvesting pink salmon, with fisheries predominantly concentrated on the east coast of Sakhalin.
Historically, fish traps were used to supply fish for commercial canning and salting in North America, starting in the late 19th century. However, the use of fish traps declined drastically in the 1940s and 1950s, coinciding with a sharp decline in pink salmon populations. Alaska banned fish traps in 1959, and since then, purse seines, drift nets, and gillnets have become the primary methods for catching pink salmon. Populations and harvests have experienced a rapid increase since the mid-1970s and have consistently reached record highs since the 1980s.
Fishery-enhancement hatcheries, particularly in the northern Gulf of Alaska, produce over 20 million harvested pink salmon. These hatcheries play a significant role in augmenting pink salmon populations. Unlike other salmon species, pink salmon are not extensively grown in fish farms. Pink salmon are commonly canned, smoked, or salted, and their roe is harvested for caviar, which is particularly valuable in Asian markets. However, there is evidence to suggest that the pink salmon fishery industry may have an impact on the size of pink salmon and other salmon species, as well as the abundance of species that compete for and serve as their food sources.