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Seafood Watch® Wild Pacific Salmon Report October 8, 2010 Coho Salmon (Oncorhynchus kisutch) Coho salmon is also known as “silver” salmon. Of the five main Pacific salmon species, coho have proven to be the species perhaps most vulnerable to human pressure. While coho occupy the widest range of freshwater habitat types, they are not the most abundant species and have seen their numbers decline substantially throughout the southern portion of their range (Olsen et al. 2003). Distribution In North America, coho salmon spawn in many locations between the San Lorenzo River in Monterey Bay, California and Point Hope, Alaska in the Chukchi Sea (PFMC 2003). At sea, coho salmon range throughout the Pacific, from as far south as Baja California to Kotzebue Sound in the north. They are most frequently found in coastal waters between Central Oregon and Southeast Alaska (DFO 2001, PFMC 2004c). On the Asian side of the Pacific, coho salmon range throughout the Aleutian Islands, Kamchatka Peninsula, Hokkaido, Japan, and Korea (DFO 2001). ESUs Seven evolutionarily significant units (ESUs) of coho salmon have been identified on the West Coast of the United States: • Central California (Endangered under California Endangered Species Act) • Southern Oregon/Northern California Coasts • Oregon Coast • Lower Columbia River • Puget Sound/Strait of Georgia • Southwest Washington • Olympic Peninsula As of 2008, the Central California ESU is listed as endangered, the next three ESUs above were listed as threatened species, while the Puget Sound/Strait of Georgia ESU has a “species of concern” designation, all under the U.S. Endangered Species Act (NMFS 2010a). Additionally, coho south of Punta Gorda in California are listed as Endangered under the California Endangered Species Act. In Alaska, fishery managers have not divided coho salmon into ESUs. Instead fishery management is divided along geographic lines, splitting the state harvest into four overarching regions: Southeast Alaska, Central Region, Westward Region, and Arctic-Yukon-Kuskokwim Region. Coho salmon are harvested in all four of these regions, with a slight majority of landings coming from Southeast Alaska (Plotnick and Eggers 2004). Life History Traits Like the other species of Pacific salmon, coho salmon are anadromous, and generally have a life history similar to Chinook salmon. However, there are some differences between Chinook and coho salmon. Unlike Chinook salmon, the amount of time coho salmon spend in fresh and salt water is relatively fixed. Juvenile coho typically spend at least a year in freshwater, followed by 25
Seafood Watch® Wild Pacific Salmon Report October 8, 2010 18 months at sea, predominantly maturing at age-three (PFMC 2004a). However, in Southeast Alaska and Alaska’s Central Region, the majority of coho salmon adults are four year-olds, having spent an additional year in fresh water before going to sea (NWFSC 1995). As with Chinook salmon, precocious jacks will return to spawn at a younger age, typically just spending 5-7 months at sea. The maximum reported age for coho is five years (Froese and Pauly 2004). Unlike Chinook salmon, where most production comes from mainstem spawning areas, 8 coho salmon tend to use smaller streams and tributaries. While coho salmon are capable of utilizing the full range of freshwater environments, most coho spawning is found in “smaller, lowgradient streams and tributaries” (PFMC 2004a). Typical coho populations are small in size, and they tend to spawn late in the year (early fall to mid winter) and utilize distant headwater streams (Olsen et al. 2003). With respect to reproductive capacity, female coho salmon typically deposit several thousand eggs, which develop during the winter and hatch in early spring. The emergent fry occupy shallow stream margins, and, as they grow, establish territories, which they defend from other salmonids. Coho fry live in ponds, lakes, and pools in streams and rivers, usually along stream banks, in quiet areas free of currents. During the fall, juvenile coho may travel miles before locating to an off-channel habitat where they pass the winter free of floods. Some fish leave fresh water in the spring and rear in brackish estuarine ponds and then migrate back into fresh water in the fall (Elliott 1994). Little is known about the ocean migrations of coho salmon. Coho appear to not migrate as far as other species of salmon, staying fairly close to shore (DFO 2003). High seas tagging indicates that maturing Southeast Alaska coho move northward throughout the spring and appear to concentrate in the central Gulf of Alaska in June. In the Gulf, the fish prey on gonatid squids and a wide range of other organisms such as fish, euphausiids, amphipods, and copepods (Kaeriyama et al. 2004). The salmon later disperse towards shore and migrate along the shoreline until they reach their stream of origin (Elliott 1994). Habitat As with Chinook salmon, coho salmon have lost a considerable portion of their habitat, particularly in the southern half of their range. The same sources of habitat degradation (i.e., dams, water diversion, siltation, introduced species, and other human activities) have equally affected coho salmon. The current ESU listings indicate that coho salmon runs have been highly compromised in the contiguous states (Figure 1.4). In fact, coho salmon appear to be more vulnerable to habitat loss than other species. This additional vulnerability stems from at least three factors. First, while coho salmon populations are highly adaptable and can be found in a range of freshwater environments, many coho salmon rely on distant headwaters for spawning grounds (Elliott 1994). The longer lengths of freshwater migration leave the species more vulnerable to habitat disruption and loss from hydropower projects or water diversion en route. Second, the number of fish in coho runs tends to be smaller owing in part to the lesser tributaries coho prefer. Third, coho exhibit significant genetic diversity, with only weak “geographic concordance.” Because populations of coho are small 8 Stream-type Chinook do not spawn in mainstem areas. They are also likely to make long migrations into the interior. 26
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