Coho Salmon

Oncorhynchus kisutch

Description

The coho salmon, also known as the silver salmon, has a trout-like, elongated, moderately compressed body. The mouth is terminal and large. The upper jaw extends beyond the back of the eye, and the snout is narrowly rounded. The upper jaw becomes strongly hooked in spawning males. Coho have well-developed teeth in both jaws, and also on the palate and tongue. Pre-spawning adult coho are colored metallic blue on the back, and silvery on the sides and belly. They have irregular black spots on the back and upper lobe of the caudal fin. The flesh along the base of the teeth on the lower jaw is pale, and the body flesh is colored pink to red. The sexually mature males in freshwater have a brilliant red stripe on their sides, bright green on the back and head, and are often dark on the belly. The females are less strongly colored, and are usually bronze to pinkish-red on the sides.

Behavior

Coho salmon are born in the headwaters of rivers, and spend the first 18 months of their life there. They then migrate to the ocean, where they feed and grow for several years. When they reach sexual maturity, they return to the headwaters of their natal stream, where they breed, and die. Coho feed on aquatic invertebrates when small, graduating to smaller fish, and then to bigger fish as the salmon become larger predators.

Habitat

The freshwater habitat of coho in headwater streams is characterized by cool, clean water. They breed in beds of clean gravel, and this is also where the larvae live. Fingerling-sized and larger life stages in freshwater live in deeper water, such as pools. During the marine phase of their life history, coho live in open-water (or pelagic), cool-temperate regions of the northeastern Pacific Ocean.

Distribution

The historic range of the coho in the lower 48 states included coastal streams of California, Oregon and Washington, plus the much larger Sacramento and Columbia river systems, reaching as far inland as Idaho. It also occurs in rivers throughout coastal British Columbia and western Alaska.

Threats

During the twentieth century, the coho has decreased to as little as 1% of its former abundance in its southern range (in California and Oregon). It is extirpated in more than half of its native rivers in that region. The decline of the coho stocks of California and Oregon has been caused by several, interacting factors. Much of their freshwater habitat has been degraded by siltation and temperature increases caused by logging and other disturbances in the watersheds of their breeding and rearing habitats in headwater streams. Clear-cut logging in the riparian (or stream-side) zone results in large increases in the summertime water temperature, which can be lethal for these cool-water fish. In addition, the erosion of soil from destabilized stream-banks and at road crossings results in the deposition of silt into the gravel spawning and larval-rearing habitat of salmon, which smothers the eggs and larvae. Moreover, many rivers have had hydroelectric dams constructed on them, and this prevents or impedes the migration of coho to and from the sea. Other threats to coho include erosion associated with overgrazing of livestock, in-river mining of gravel or gold, urban and industrial pollution, agricultural diversions, and urbanization. In addition, stocks of coho salmon are heavily fished at sea and when they are migrating to their breeding habitat. In many cases, the fishing pressure is excessive (this is known as overfishing), and is a further reason why stocks are declining. These factors have affected coho salmon throughout their range on the Pacific coast, but the damages have been most intense for stocks breeding on coastal rivers in California and Oregon. Overall, the coho has become extirpated over about 56% percent of its historic range in the lower 48 states, endangered in about 13%, threatened in about 20%, and of special concern in 5%. In California, for example, about one-half million coho inhabited rivers in the state in the 1940s, but only a few thousand survived in the 1990s. The coastal rivers of Oregon produced about 1.4-million coho in 1900, but fewer than 20,000 in the 1990s. In Washington, the 1.2 million coho that once lived in the Columbia basin are virtually extinct.

Conservation and Recovery

Listing of the threatened stocks of coho in California and Oregon has been a highly contentious and politicized process. The environmental and fishing communities have exerted pressure to list these stocks under the Endangered Species Act. However, this action been resisted by interests in the timber industry, agribusiness, and state governments, who fear restrictions on their activities in order to conserve coho habitat. Finally, in 1999, the National Oceanic and Atmospheric Administration (NOAA) listed the status of coho as "threatened" in the following regions: Central California; Southern Oregon/Northern California Coasts; and Oregon Coast. In addition, coho were judged as "Candidate for Listing" in the following regions: Puget Sound/Strait of Georgia; and Lower Columbia River/Southwest Washington. The key to saving the threatened and depleted stocks of coho in coastal California, Oregon, and Washington is to preserve their small remaining areas of high-quality freshwater habitat in headwater streams. In large part, this requires close restrictions on logging and road building in the watersheds. Moreover, many degraded habitats will have to be managed to improve conditions, particularly in terms of mitigating heavily silted gravel beds. It will also be necessary to restock some populations that have been extirpated, and to strictly prohibit continued fishing of adult coho until the stocks have been rebuilt.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

National Marine Fisheries Service, Protected Resources Division
525 N. E. Oregon Street, Suite 500
Portland, Oregon 97232
Telephone: (503) 230-5400

References

National Oceanic and Atmospheric Administration.April 18, 2000. "West Coast Salmon and the Endangered Species Act. Listing Status: Coho." Protected Resources NOAA Fisheries and National Marine Fisheries Service: The Endangered Species Act. (http://www.nwr.noaa.gov/1salmon/salmesa/cohoswit.html). Date Accessed: July 6, 2000.

Sierra Club. 1999. "Spotlight on Species, Coho Salmon: Oncorhynchus kisutch." Sierra Club. (http://www.sierraclub.org/habitat/coho.asp). Date Accessed: July 6, 2000.