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Seafood Watch® Wild Pacific Salmon Report October 8, 2010 Pink Salmon (Oncorhynchus gorbuscha) Pink salmon are the smallest of North American salmon, with adults weighing on average less than four pounds and measuring under two feet long (PFMC 2004a). Pink salmon (pinks), also known as “humpback” salmon because of the pronounced hump that develops on the backs of mature adult males, maintain a two-year lifecycle, thus large runs follow a biennial pattern. Distribution Pink salmon are found on both sides of the North Pacific. On North American shores they extend from Puget Sound north to Alaska and the Aleutian Islands. In Asia, pink salmon spawn between Russia, North Korea, and Hokkaido, Japan, and range into the Bering and Okhotsk Seas (Hard et al. 1996, Froese and Pauly 2004). In latitudinal terms, pink salmon currently spawn around the Pacific Rim from 44°N to 65°N in Asia and from 48°N to 64°N in North America (Hard et al. 1996). Currently, Washington appears to be the southern limit of the spawning distribution of pink salmon in North America (Hard et al. 1996); however, historic pink drainages may have stretched further south into California (Brownell 1999, Froese and Pauly 2004). ESUs The National Marine Fisheries Service has not identified geographically-specific ESUs for pink salmon in the Pacific Northwest. It has identified, however, odd- and even-year runs, but neither odd- nor even-year pink salmon runs have been listed as threatened or endangered (NMFS 2004a). In Alaska, pink salmon are not divided by ESUs. Fishery management is instead divided into four overarching regions: Southeast Alaska, Central Region, Westward Region, and Arctic- Yukon-Kuskokwim Region. Of these four regions, pink salmon are predominantly harvested in the first three (Plotnick and Eggers 2004). Life History Traits Adult pink salmon enter spawning streams between late June and mid-October (Kingsbury 1994, Hard et al. 1996). Most pink salmon spawn within a few miles of the coast and spawning within the intertidal zone or the mouths of streams is common (Steelquist 1992, Kingsbury 1994). Shallow riffles, where flowing water breaks over coarse gravel or cobble-size rock, and the downstream ends of pools are favored spawning areas (ADFG 2000). Female pink salmon each carry 1,500 to 2,000 eggs depending on her size (Steelquist 1992, Kingsbury 1994, Hard et al. 1996). As with the other species of Pacific salmon, females dig nests, or redds, with their tails and release the eggs, which are then fertilized by males and covered over. The process is commonly repeated several times until all of the female's eggs have been released, after which the spawning adults soon die, usually within two weeks (Kingsbury 1994). Sometime during early to mid-winter, eggs hatch. The alevins, or young fry, feed on attached yolk sac material, and continue to grow and develop (Kingsbury 1994). In late winter or spring, the fry swim up out of the gravel and migrate downstream into salt water. The emergence and outward migration of fry is heaviest during hours of darkness and usually lasts for several weeks before all the fry have emerged (Kingsbury 1994). Following entry into salt water, juvenile pink salmon move along the beaches in dense schools near the surface, feeding on plankton, larval fishes, and occasional insects (Steelquist 1992, 33
Seafood Watch® Wild Pacific Salmon Report October 8, 2010 Larsen et al. 2004a). Predation is heavy on the very small, newly emerged pink salmon fry, but growth is rapid. By fall, at an age of about 1 year, juvenile pink salmon are 4 to 6 inches long and are moving into ocean feeding grounds in the Gulf of Alaska, the Aleutian Islands, and the Puget Sound areas (Kingsbury 1994, Hard et al. 1996). High seas tag-and-recapture experiments have revealed that pink salmon originating from specific coastal areas have characteristic distributions at sea which are overlapping, non-random, and nearly identical from year to year (Kingsbury 1994). The ranges of Alaska pink salmon at sea and pink salmon from Asia, British Columbia, and Washington overlap each other (Kingsbury 1994). Once at sea, pink salmon in the Gulf of Alaska prey on a wide diversity of organisms (e.g., squids and zooplankton), and show a high degree of plasticity in their diets, readily changing between types of prey in response to their availability (Kaeriyama et al. 2004). Pink salmon almost exclusively mature in two years, which means that odd-year and even-year populations are essentially unrelated. Frequently in a particular stream or region the odd-year or even-year cycle will predominate, although in some streams both odd- and even-year pink salmon are about equally abundant. Occasionally cycle dominance will shift, and the previously weak cycle will become most abundant (Kingsbury 1994). At present, pink salmon in the Pacific Northwest are most abundant during odd-numbered years. In terms of homing, it is interesting to note that pink salmon may have a higher degree of straying than other species, and occasionally use streams as far as 640 km from their natal waters (Froese and Pauly 2004). The high incidence of straying helps to explain why pink salmon have fewer distinct ESUs than other Pacific salmon. Habitat As with sockeye and chum salmon, most pink salmon habitat is found in Alaska and has been relatively unperturbed. Historic spawning populations in California have already been eliminated, and remaining spawning habitat in the Pacific Northwest has been compromised to the extent that it no longer fully supports robust populations (Figure 1.7); of the 15 populations of pink salmon in Washington only 6 are classified as healthy. Because pink salmon typically spawn within a few miles of the coast, they have been less affected by the development of hydropower projects and upstream water diversion than have other salmonids. 34
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