salmon, in zoology

Introduction

salmon sămˈən [key], member of the Salmonidae, a family of marine fish that spawn in freshwater, including the salmons, the trouts, and the chars (subfamily Salmoninae), the whitefish and the ciscoes (subfamily Coregoninae), and the grayling (subfamily Thymallinae). The Salmonidae are characterized by soft, rayless adipose fins, and are denizens of cold, oxygen-rich waters. In general they are silvery in the sea and more brightly hued in brooks and lakes.

Classification

Salmon are classified in the phylum Chordata, subphylum Vertebrata, class Actinopterygii, order Salmoniformes, family Salmonidae.

Conservation and Aquaculture

Because of such human activities as overfishing, development, dam building, logging, and farm irrigation, Pacific salmon populations have greatly declined, and many species are now listed as rare and endangered. The United States and Canada negotiated a conservation agreement in 1999 that includes setting catch limits based upon ongoing scientific assessments of salmon population levels. In addition, multiple-approach conservation efforts are under way in Washington and Oregon states to restore the salmon runs. For reasons less well understood, and despite international conservation measures, Atlantic salmon populations have also sharply declined.

The desirability of salmon as food fish has led to their being raised in aquaculture. The primary species that are farmed are Atlantic salmon, rainbow trout, coho salmon, and chinook salmon. Nearly all the Atlantic salmon sold is produced by aquaculture. Norway, Chile, Canada, the British Isles, Russia, Australia (Tasmania), and the states of Washington and Maine are the main areas where salmon is farmed; in many of these areas the farmed fish, typically Atlantic salmon, is not native. Most of the wild salmon caught in the United States is initially raised in fish hatcheries and then released into the wild.

Life Cycle

The basic life pattern of the Salmonidae begins when, within the first year or two of life, the fish travels downstream to the sea, where it grows to its full size. After reaching maturity (one to nine years) it returns to its hatching site to spawn. The Pacific salmon are famed for their grueling journeys of hundreds of miles to their headwater breeding grounds. When they begin this trip they are in prime condition, but they cease eating when they leave the sea and arrive months later, exhausted and battered by their fight upstream against swift currents and over falls. Those that survive the trip and escape fishermen and predatory animals spawn with their last strength and then die. These salmon are taken at the mouths of large rivers, as they begin their upstream migration. The Atlantic salmon and the trouts spawn more than once. Most trouts migrate to the sea if there is a cold-water connection, but also will sometimes live and reproduce if landlocked.

Salmons, Trouts, and Chars

Salmo (the Atlantic salmon and trout), Oncorhynchus (the Pacific salmon and trout), and Salvelinus (chars) are the largest of the several genera in the subfamily Salmoninae. Unfortunately, the common names of the species do not correspond to the natural divisions. The speckled, or brook, trout of the E United States, for example, is a Salvelinus and should more properly be called a char, as similar fishes in Europe are. The brown trout and many other species called trouts are members of the genus Salmo.

The only native North American species of Salmo is the Atlantic salmon. The Atlantic salmon was a plentiful source of food for the Native Americans and the colonists, but its populations have declined. A large fish (15 lb/6.8 kg average), it is found along the Atlantic coast of NE America, in Greenland, and in Europe. When in the sea it feeds on crustaceans, but as it approaches the the large rivers to spawn, it changes its diet to small fish. A landlocked form of the Atlantic salmon, the Sebago salmon, is found in Maine. The brown trout, a Salmo species introduced from Europe in 1883, requires warmer waters than the native species of trout and is important in fish-management programs. The term brown trout is used for freshwater forms of the fish; those that are largely marine are known as sea trout.

The genus Oncorhynchus is comprised of a dozen species of Pacific salmon and trout, found from S California to Alaska. Pacific salmon are the most important commercial species. Canning centers are located on the Columbia River and on Puget Sound and in British Columbia, Siberia, and N Japan. The largest and commercially most important of the Pacific salmon is the chinook (or quinnat or king) salmon, which averages 20 lb (9 kg) and may reach 100 lb (45 kg). It is found from the Bering Sea to Japan and S California and is marketed fresh, smoked, and canned. The white-fleshed fish of this normally red-fleshed species have become highly prized in the restaurant trade. The blueback salmon (called sockeye in Oregon and redfish in Alaska) has firm reddish flesh and forms the bulk of the canned salmon. Also of economic importance are the humpback, or pink, salmon, the smallest of the group; and the silver, or coho, salmon, important in the fall catch because of its late spawning season. The meat of the dog salmon is palatable when fresh or smoked. Among the trouts in this genus are the rainbow trout and cutthroat trout. The steelhead trout, also known as the salmon trout and ocean trout, is the silvery saltwater phase of the colorful rainbow trout. Of the many races of cutthroat trout, some are now extinct.

The genus Salvelinus includes the various European chars; the common brook, or speckled, trout, a popular game fish of E North America, introduced in the West; and the Dolly Varden, or bull, trout, a similar western form. The largest of the chars, the common lake trout of North America, is a deepwater fish of lakes, more sluggish, less migratory, and bulkier than the other Salmoninae. Individuals have been recorded at 100 lb (45 kg). A fish called the splake has been produced by crossing the speckled trout and the lake trout.

Bibliography

See A. Netboy, The Salmon: Their Fight for Survival (1973).

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