This species is listed as Least Concern in view of the large extent of occurrence (EOO), large number of subpopulations, large population size, and lack of major threats. The trend over the past 10 years or three generations is uncertain but probably relatively stable, or the species may be declining but not fast enough to qualify for any of the threatened categories under criterion A (reduction in population size). However, it should be noted that treatment at species-level masks many significant declines that are in progress and well documented.

The native range includes the Pacific Ocean and tributary drainages, in eastern Asia from the Anadyr River south to northern Japan and in North America from Point Hope, Alaska, south to central California and infrequently at sea as far south as Baja California, Mexico. The species is most abundant between Oregon and south-eastern Alaska, and rare south of central California. In Asia it has been recorded from Chukotka to the south along the Asian coast up to the Peter the Great Bay, and to the Korean Peninsula, including Kamchatka, the Komandorskiye and the Kuril Islands (Shumshu, Paramushiro, Urup, Iturup, and Kunashir), Hokkaido Island and the Pacific side of northern Honshu (Japan).

It has been widely stocked in lakes and reservoirs throughout North America and elsewhere.

See Frissell (1993) for a map indicating present and former distribution in the Pacific Northwest and California. See Moyle et al. (1989) for further information on distribution in California.

Total adult population size is unknown but relatively large.

In a survey of populations in the contiguous U.S., Huntington et al. (1996) identified only three healthy native stocks, all in Washington. Of 2,594 stocks in British Columbia and Yukon, Slaney et al. (1996) categorised 29 as extirpated, 214 as high risk, 22 as moderate risk, 21 as special concern, 1,024 as unthreatened, and 1,284 as unknown status. In the 1900s, indigenous, naturally reproducing populations are believed to have been extirpated in nearly all Columbia River tributaries and to be in decline in numerous coastal streams in Washington, Oregon, and California; at least 33 populations have been identified by agencies and conservation groups as being at moderate to high risk of extinction (NMFS 1995); at least 15 stocks in the contiguous U.S. have been extirpated (Nehlsen et al. 1991). Wild fish are increasingly rare throughout the range, especially at the southern and eastern parts of the range (see Nehlsen et al. 1991 for a review of the status and declines of these populations). It is stable or increasing in a portion of northern California and in north-western Washington; but special concern, threatened, endangered, or extirpated elsewhere (see map in Frissell 1993). In California, populations fluctuate, but the general trend seems to be downward for wild, short-run populations in small coastal streams. The population of Lake Khalaktyrskoye in Kamchatka, according to the available data, is on the verge of extinction under the influence of anthropogenic pollution and poaching (Reshetnikov 2002, Tokranov and Sheiko 2006).

This is an anadromous species, with lake and residential forms, represented by isolated populations. Upstream migration in rivers from June to December. Usually fish of 40-80 cm length and 1.2-6.8 kg weight enter the rivers. For spawning, it enters native rivers in the third to fourth (rarely in the fifth) year of life. Coho Salmon usually spend two (range 1-3) growing seasons in the ocean before spawning. In the ocean, they remain over the continental shelf and generally stay within 30 km of their natal stream (but some may range up to several hundred kilometers away). The lake forms mature in the fourth year. Spawning grounds are located from river mouths to upper reaches. Spawning occurs in just about any accessible coastal stream, generally in forested areas, usually at 6-12^oC in loose coarse gravel at heads of riffles (or tails of pools) in rounded troughs excavated by females where water is 10-54 cm deep. Females construct and deposit eggs in each of several redds. Individuals generally spawn in their natal stream; however, rapid colonization of newly accessible habitat has been observed. Spawning on sites with outlets of groundwater from late August to early winter. Stocked populations in lakes and reservoirs migrate upstream to spawn or more commonly do not reproduce (must be restocked annually). The fecundity of Coho Salmon is 2,800-7,600 eggs in Kamchatka and 1,700-9,000 in rivers of the Okhotsk Sea coast. Eggs are relatively small with a diameter of 4.5 mm. After spawning all fish die. Larvae hatch in 86-100 days depending on temperature. Young spend a few weeks to three years (varies geographically) in freshwater streams before migrating to the sea (young in the north spend a longer time in fresh water than do those in the south). Often this period is substantial and amounts to approximately half of the life cycle. Hatchlings that have left the spawning site seek shallow water, usually along stream margins. Older juveniles prefer pools and runs with good cover, high oxygen levels, and abundant invertebrate populations. Fry may summer in brackish water in south-eastern Alaska. The main mass rolls down in the second year of life (less often in the third or fourth year). Young feed on insects and insect larvae, eggs of other fish. Downstream run takes place in June-August. Coho Salmon spends more than a year in the ocean south of the Aleutian Islands in waters with temperatures from 5 to 10^oC (Reshetnikov 2002).

The resident form in lake populations of Kamchatkaretains generally has a population structure common to the species and can exist both completely independently of the anadromous forms (Lake Kotel’noye) and together (Lakes Sarannoe, Golyginskoe and Khalaktyrskoe). In various lakes it matures in the second, third or fourth years of life. Spawning of resident Coho Salmon begins in the end of October and is considerably stretched in time. Fecundity is 600-2,000 eggs. It feeds mainly on chironomids, molluscs and air insects. Macrophytes are often found in the stomachs of Coho Salmon from Lake Kotel’noye, a phenomenon unknown in other populations. Some fish of older age groups switch to predation, so they have a sharp increase in growth rate. Length reaches 53 cm, body weight 2.1 kg, and longevity 4-5 years (Tokranov and Sheiko 2006).

Many populations have been negatively impacted by logging, agricultural activities, overgrazing, urbanisation, stream channelisation, wetland loss, and poor watershed management practices that increase stream temperatures, cause siltation, or otherwise destroy or degrade habitat. Road construction also has negatively altered many smaller coastal streams. Dams, water withdrawals, and unscreened diversions for irrigation also have contributed to the decline. Poor ocean conditions (e.g., El Nino conditions) are believed to have played a prominent role in the decline of populations in Washington, Oregon, and California (NMFS 1995). The effects of extended drought on water supplies and water temperatures are a major concern for California populations of Coho Salmon.

Native populations are most at risk in the southern and eastern parts of the range, largely as a result of habitat degradation mentioned above and also the negative effects of  hatchery programs (Nehlsen et al. 1991). Potential problems associated with hatchery programs include genetic impacts on indigenous, naturally reproducing populations, disease transmission, predation on wild fishes, difficulty in determination of wild run status due to incomplete marking of hatchery releases, and replacement (rather than supplementation) of wild stocks through competition and continued annual introductions of hatchery fishes (NMFS 1995). It is difficult to assess the degree to which recreational and commercial harvest have contributed to the decline. Commercial fisheries in California and Oregon have been greatly reduced or closed since the early 1990s.

In some regions, overharvesting is a threat and in recent years, according to official statistics, about 2,000 tons have been extracted annually, but the so-called unaccounted-for catch (poaching, fishing by private firms, etc.) is also growing annually (Antonov et al. 2009).

See NMFS (Federal Register, 6 May 1997) for further information on threats.

This species is an important fishing target, both legal and illegal (North Pacific Anadromous Fish Commission 2020).

Recovery in the southern part of the range is challenging due to the large legacy of intense industrial logging and enduring impacts of large floods in the mid-20th Century (Moyle et al. 1989).

Hatcheries contribute to much of production in the southern part of the species' range (Hassler 1987). Meffe (1992) gave reasons why the hatchery approach to recovery ultimately will fail, and he emphasized that overharvest and habitat destruction need to be addressed in a major landscape-level effort. See Thomas et al. (1993) for information on habitat management for this and other at-risk fish species in the Pacific Northwest.

Stocks transplanted to non-native streams exhibit reduced survival (see Williams et al. 1992).

Waples and Teel (1990) emphasised the importance of monitoring the genetic consequences of the large-scale artificial propagation programs involving Pacific salmon (see also Waples 1990).

It is recommended to: determine genetic variation among wild populations in different streams; survey potential spawning streams for evidence of successful reproduction; protect spawning and rearing (juvenile) habitats; and taking into account its low number in all lakes of Kamchatka and Komandorskiye Islands, it is necessary to limit harvesting and forbid it in Khalaktyrskoye Lake (N. Bogutskaya pers. comm. 2020). See Nehlsen et al. (1991) for general protection and management recommendations for anadromous salmonids.

The lake resident form is listed in the Red Book of Kamchatka (Tokranov and Sheiko 2006) and at present catches of resident Coho Salmon are regulated by the existing Fisheries Regulations.

While focus on species-level status assessments are an important first step, the IUCN Species Survival Commission (SSC) Salmon Specialist Group (SSG) emphasizes the need to characterize status of Pacific Salmon at a more granular, population-level scale (identified as “subpopulations” in the IUCN Red List Guidelines) to provide meaningful guidance to stem the loss of biodiversity across the natural range of the species. There are many examples of declines in wild Pacific Salmon in both North America and Asia, particularly in the southern portion of their range given the degree of degradation and fragmentation of habitat there and the more immediate risk of climate change impacts. At the same time, there are large-scale ocean drivers that appear to be affecting species broadly across the North Pacific, regardless of their freshwater origin. Two excellent examples exist of assessment approaches and policies in the US (Waples 1991) and Canada (DFO 2005, COSEWIC 2018) that establish an effective framework for Pacific Salmon conservation. These efforts involve identifying population units based on a variety of criteria including examination of traits that are important in the evolutionary process and future adaptation. In these examples, assessments are conducted at a more granular, population-level, resulting in listings for individual population units, with identification of needed conservation actions specific to each unit. An example of assessing range-wide status of the species and at the individual subpopulation level in the IUCN Red List now exists for Oncorhynchus nerka (Rand 2011). While the amount of effort required to rigorously assess the species is substantial, we encourage efforts like this applied to the other species in the genus.