Salmon

The salmon family Salmonidae comprises numerous landlocked and anadromous species (Fig. 7). They are found in most waters of the northern hemisphere and dominate the northern waters of North America, Europe, and Asia. This family is made of of three subfamilies, the Salmoninae (salmon, trout, char), the Coregoninae (whitefish), and the Thymallinae (grayling). A common feature among all species is the adipose fin located on the dorsal surface between the dorsal and caudal fins. While representatives of the Coregoninae and Thymallinae belong to this family, the term salmon is usually applied to the salmon and trout of the Salmoninae. This article deals with only those species that are commonly referred to as salmon, which includes species in the genera Oncorhynchus and Salmo. Even this restriction does not eliminate the confusion between common names and the scientific classification. The Atlantic salmon, for example, is strictly classified as a trout in the genus Salmo. The rainbow trout, on the other hand, has just recently been transferred from the genus Salmo to Oncorhynchus, but it continues to be called a trout. The species covered here include the Pacific salmon species, the rainbow trout, and the Atlantic salmon.

The anadromous species spawn in fresh water where the eggs incubate and where the young spend varying lengths of time. It is common for adults to return to the streambed where they were hatched. During the sexual maturation process, the typically silver fish begins to darken and takes on various colors including black, brown, orange, and red. There is usually a dramatic transformation of the shape of the head and in some instances, the whole trunk. The head of the male usually elongates and there is a pronounced development of teeth. The chum salmon, for instance, develops a large hump back during this process. Many species do not feed once they enter fresh water and begin their migration to their spawning grounds. The spawning process culminates a long journey, sometimes covering thousands of miles, and normally ends in death for the Pacific salmon. The trouts, on the other hand, usually recuperate and may return to spawn a number of times. The Pacific salmon, Atlantic salmon, and steelhead trout are anadromous. The landlocked salmo-nids discussed in this article include the rainbow trout and the kokanee salmon. While these are the natural life cycles, some species can be grown entirely in fresh water. For example, rainbow trout can be grown quite successfully in seawater netpens and the coho and pink salmon can spend their entire life cycle in fresh water.

Figure 7. Rainbow trout (Oncorhyn-chus mykiss). Source: Copyright 1990 by B. Guild-Gillespie.

Figure 7. Rainbow trout (Oncorhyn-chus mykiss). Source: Copyright 1990 by B. Guild-Gillespie.

Spawning behavior typically involves a high degree of territoriality and aggression between individuals as mates selection takes place. The female will usually create a depression, called a redd, in the gravel bottom by beating the rocks with the side of her tail. After eggs and milt are deposited simultaneously for fertilization to take place, the female will cover the eggs with gravel by moving upstream from the redd and making another redd, causing the displaced gravel to cover the first redd that contains the eggs. The fertilized eggs then incubate in fresh water, which percolates through the gravel, supplying oxygen and carrying away metabolic products such as ammonia and carbon dioxide. The developing embryos as well as the hatched alevins live off yolk carried in a yolk sac while they are still under the gravel. After the yolk is consumed, their mouths open and they begin to emerge from the gravel and feed on organisms in the open waters of the stream. The young of anadromous fishes spend varying lengths of time in fresh water. This fresh water residence ends when the animal undergoes the process of smoltification. This is the total of behavioral, morphological, and physiological changes that occur in the juvenile fish to prepare it for life in salt water. After the process of smoltification, the young migrate to sea to spend the rest of their life cycle growing to sexual maturity.

Pacific Salmon

Chinook Salmon. The chinook salmon (Oncorhynchus tshawytscha) is one of the most prized fishes on the west coast of North America. It is also one of the most important commercial species. The chinook salmon is known as the tyee or king salmon when the body size reaches greater than 13.6 kg. This fish has the largest body size of the Pacific salmons. While 13.6 kg is more common as the maximum size, the world's record is 57.3 kg. It is this characteristic combined with its high market value that has made it a popular choice for aquaculture in the northwestern states and on the west coast of Canada. There are two varieties of chinook salmon, the red chinook and the white chinook, which are named according to their flesh color. The red flesh commands the higher price. This segregation is rather unique among the salmon. Chinook salmon are caught commercially with trolling gear, purse seine or gill nets, long lines, and fish wheels. The majority are caught by trollers. Chinook salmon are sold as fresh, frozen, and canned products, with the canned products coming from the net fishery. They are caught for sport with a variety of lures including artificial lures, bait, and fiys. Dead herring serve as a desirable bait, trolled deep in the water column.

Chinook salmon adults migrate extensively and are primarily found in the Pacific Ocean from the Ventura River in southern California, north to Point Hope, Alaska. Limited evidence suggests, for instance, that the Canadian shi-nook migrate north to the Gulf of Alaska but remain within 160 km of that area until they return south to spawn. This species is less common in the Arctic Ocean and in the Bering and Okhotsk seas and the Sea of Japan. The largest numbers come from the largest rivers such as the Fraser River in British Columbia. Substantial numbers of chinook also come from the Yukon River. While there have been numerous attempts to transplant this species to many locations throughout North America and around the world, it seems that only success was on South Island, New Zealand, where a self-supporting population was established.

The average age of an adult returning to spawn varies from four to seven years, depending on the location. Three-to five-year-old returning adults are more common in southern streams, whereas five- and six-year-old adults are more common in northern streams. It is also quite common for river systems to have more than one stock of chinook salmon returning to it, where there may be spring, fall, and winter runs of returning adults.

The time of spawning depends on the location and the distance the adults must swim upriver to reach the spawning grounds. In the Fraser River, for example, the chinooks spawn between July and November and the adults may travel up to 965 km from the mouth of the river to their spawning grounds. The chinooks that return to the Yukon River spawn between July and August and may travel up to 1930 km to reach their spawning grounds. Other stocks that travel only a few miles, if that, in British Columbia spawn in September and in October. Chinook salmon tend to spawn in deeper waters and in larger gravel than other Pacific salmon species. Each female may carry from 4,000 to 13,000 eggs. The eggs are large for fish eggs and measure about 7 mm in diameter. The eggs hatch the following spring and the alevins spend two to three weeks in the gravel with their yolk sacs. The emergent young remain in the freshwater rivers for varying lengths of time, depending primarily on the water temperature. The young will smolt and migrate to sea after about three months in warmer southern areas such as in southern British Columbia, while chinook spend at least one year in fresh water in northern areas. Chinook juveniles may spend two years in fresh water in the Yukon River. The maturing adults may spend two to three years at sea before returning to fresh water to spawn. Spawning females are, therefore, about four to five years old.

Coho Salmon. The coho salmon (Oncorhynchus kistuch) is also an important commercial and sport fish in North America. It is the mainstay of the saltwater sport fishery for salmon. Most of the coho are commercially caught in August by trolling with plugs, spoons, or feathered jigs, although purse seines and gill nets are also used. The trolled catch is sold as the fresh or freshly frozen product, while the netted fish are either canned or smoked. Sport fish are caught in the late summer to early fall months of July to October. The gear used by sport anglers is similar to the commercial trolling gear except it is smaller in size. Coho are also caught on the fly with bucktail flies and with bait such as frozen or pickled herring. Because coho remain silver and continue to feed while traveling upstream to spawn, they are pursued by the sport angler in many freshwater rivers and streams.

The adult distribution extends from southern California to the Gulf of Alaska. The juveniles are found in the fresh waters from Monterey Bay, Calif., to Point Hope, Alaska. Coho salmon are also found in the Anadyr River in the former USSR and south from that point to Hokkaido, Japan. This species has been transported to other parts of the world such as Argentina and Chile, with Chile reporting some success in the establishment of naturally reproducing stocks. Coho have also been introduced into the Great Lakes by both Canadians and U.S. citizens. While there are reports of natural reproduction, the maintenance of those stocks are heavily dependent on the annual planting of cultured stocks.

The full-grown adult can weigh from 1.8 to 5.5 kg. It enters fresh waters to spawn from late September to October and may travel up to about 240 km upriver to spawn. Asian populations exhibit more of the separation of summer and fall, or fall to winter runs than those populations returning to North American river systems. Spawning takes place in October or November. The eggs are rather large, measuring about 6—7 mm in diameter. The range in fecundity is about 2,000-3,000 eggs. After the eggs have hatched, the young spends between one and two years growing in fresh water. This again, depends on the location. Coho juveniles in British Columbia spend about one year in fresh water while those in the Yukon spend two years growing in fresh water. After their freshwater residence, the young smolts migrate to sea. The saltwater residence usually lasts about 18 months, although the phenomenon of precocious sexual maturation, or jacking, is predominant in this species. While normal adults will return between three and four years of age, jacks return to spawn at only two years of age. Coho salmon normally stay within about 40 km of the coast.

Chum Salmon. While the chum salmon (Oncorhynchus keta), or dog salmon, is a less desirable species for the commercial or sport fisheries, it has maintained an important position in the diets of the native people of North America who capture the fish with nets and fish wheels. It is a preferred species for smoking because of its low fat content. Its pale to white flesh has the lowest fat content of the

Pacific salmons. This species has been used the least for transplantations to other geographic areas, perhaps due to its relatively low commercial and sport value. Most of the chum salmon are harvested while they are migrating toward their home streams to spawn. Commercial catches are harvested mainly between August and October with purse seines and gill nets. Some are also caught by trolling gear. The trolled catch is sold fresh. Some are smoked or dry salted for preservation. The bulk of the commercial catch, however, is canned.

The marine adults are found in Pacific and Arctic oceans, in the Sea of Japan, and in the Okhotsk and Bering seas. They probably have the widest distribution among the Pacific salmons. The major spawning areas in North America lie between Puget Sound in Washington State to Kotzebue, Alaska. The geographic range for their spawning covers the west coast of North America from Oregon to the Mackenzie River. The time frame for adults arriving at the spawning grounds ranges from July, in northern British Columbia to September or even as late as January for streams further south. The location of the spawning grounds, reflecting the degree to which the chum salmon swim into fresh water to spawn, varies considerably. Most arrive at the mouths of rivers in an advanced state of sexual development and spawn relatively close to the ocean. In general, few chum salmon migrate more than 160 km from the mouth of a river to spawn. The Yukon River, however, is an exception; the population ascends over 1,930 km to spawn.

The mature adult is usually between two and four years old. While the adult chum salmon can weigh from 3.6 to 5.5 kg, fish up to 13.7 kg have been reported. The fecundity ranges from about 2,000 to 3,000 eggs and each egg measures about 5-6 mm in diameter. The hatched young spend a period in the gravel feeding off the yolk until the spring when they emerge and migrate directly to sea. Depending on the distance to the ocean, the young may take from a single night up to several months until they reach sea water. The migratory behavior of the young chum are similar to the pink salmon and the young of both species may be found making the seaward journey together. They usually travel by night and hide in the gravel during the day. They are also not dependent on schooling to make the trip, although they do school once they have reached the estuary. Once in the ocean, the young chum will usually spend a few months, until mid to late summer, in the coastal areas before migrating further out to sea. Chum salmon from North America have been captured as far as 4,180 km off the west coast in the North Pacific. Most chum salmon spend two or three years in the ocean before returning to their home streams to spawn. They begin to appear at the mouths of rivers around May or June of their final year at sea.

Pink Salmon. The pink salmon (Oncorhynchus gorbuscha) is the most abundant of the Pacific salmon species. It gets its name from the pink color of its flesh. Like the chum salmon, this species is not regarded as being highly desirable compared to the deep red flesh of the sockeye salmon. The size range of the adult is about 1.4-2.3 kg, although animals as large as 6.4 kg have been recorded. A unique characteristic of this species is its fixed, two-year life cycle.

There is no overlap between the reproducing stock of one year to the next. This allows two separate stocks to utilize any stream for reproduction. Where there are odd-year stocks as well as even-year stocks using the same river, one often dominates. The Fraser River pink salmon run in British Columbia, for example, is primarily an odd-year stock, while the run in the Queen Charlotte Islands is an even-year stock.

Pink salmon is caught commercially with purse seine and gill nets as well as with trolling gear, the latter contributing only a minor part of the total catch. Fish caught by trolling is sold fresh, but 95% of the commercial catch is canned. Pink salmon is also fished for sport by trolling artificial lures.

Pink salmon is found in the Pacific and Arctic oceans, the Bering and Okhotsk seas, and the Sea of Japan. Its distribution in North America extends from the Sacramento River in California, north to the delta of the Mackenzie River, being most abundant around the central area of this range. It can be found from the surface to depths of about 36.6 m. Transplantations have established self-sustaining populations of pink salmon in northern Europe and in fresh water in Lake Superior. There are transplanted populations along the Atlantic Coast of North America that seem to be self-sustaining.

Pink salmon may spawn in a wide range of locations from tidal areas of certain rivers up to 483 km upstream from the mouths of large rivers. The pink salmon are also known as humpbacks because the sexually mature males develop a large hump behind the head. The snout elongates dramatically and large teeth emerge from the jaws. The adults will appear at the mouths of rivers from June to September to begin their migration to their spawning beds. Pink salmon spawn from mid-July to late October and the eggs hatch from late December to late February. Like the chum salmon, the young emerge from the gravel after the yolk supply is consumed and move directly to sea. The emergent young, which measure about 3.8 cm in fork length, may travel 16 km in a single night to reach the ocean. Their appearance is distinctive for salmon in that they lack the vertical parr marks on their sides. They are colored blue-green on their back and have silver sides. If the journey takes more than a night, the young will hide during the day in the gravel and emerge again at night to be carried by the current to the sea.

Sockeye Salmon. The anadromous sockeye was the first Pacific salmon species to be fished commercially. The sockeye has long been the mainstay of the Pacific salmon fishery. Its deep red flesh and high oil and protein contents have always brought it the highest price among the Pacific salmon species on the market. The sockeye is mainly caught with purse seine and gill nets, although trolling is also used. The product is mainly canned, although it may be sold fresh when the fishery is open. Native people use traditional methods of nets, weirs, and gaffs to harvest the fish. Although the sockeye salmon are not an important sport fish, effective artificial lures have been developed that have served both sport and commercial trailers at the mouth of major sockeye rivers such as the Fraser in British Columbia.

The sockeye salmon (Oncorhynchus nerka) is represented by an anadromous form and a landlocked form known as the kokanee. Specific recognition as subspecies has been given to each. The anadromous form i O. nerka nerka Walbaum and the kokanee is designated O. nerka kennerlyi Suckley. The anatomy of the two subspecies is very similar except for the total body size. The average weight of an adult anadromous sockeye is about 2.7-3.2 kg, whereas the adult kokanee weighs less than 455 g. Adult sockeye have been recorded to be up to 6.8 kg.

The distribution of this species extends from the Kala-math River in California to Point Hope in Alaska. They are also found in Asia from northern Hokkaido, Japan, to the Anadyr River in the former USSR. The distribution of the kokanee certainly follows that of the anadromous sockeye. It occurs in lakes where the anadromous salmon must have had access at one time. Both kokanee and most anadromous sockeye return to the spawning grounds as four- or five-year-old fish. Both species spawn in the fall. The actual time depends on location. Kokanee, for example, spawn in September and October in Kootenay Lake in British Columbia but in November and December in Boulter Lake, Ontario. The major spawning grounds for this species are the watersheds draining into the Fraser, Skeena, and Nass rivers in British Columbia. Anadromous sockeye spawn between July and December, again depending on location.

Sockeye become sexually mature from three to eight years in age. While a one-year freshwater residence and a two- to three-year saltwater residence is normal, precocious males may return to spawn after only one year at sea. Fecundity is highly variable in this species. It ranges from 370 to 1760. While the kokanee egg is naturally small, the egg of the anadromous sockeye is large, measuring about 4.5-5 mm in diameter. After hatching and consuming all the yolk, the young sockeye will spend at least one year in fresh water, although some will spend two or even three years in fresh water before migrating to sea. This variability is, to some extent, responsible for the range in size of adult sockeye. These years in fresh water are spent in nursery lakes. The fry feed on planktonic organisms. Anadromous sockeye smolts will migrate to sea in the spring of their second and fifth year of life. At sea, the maturing sockeye migrate north and northwest, spreading out to the distribution outlined above.

Rainbow Trout. The rainbow trout, steelhead trout, and kamloops trout all belong to the same species, Oncorhynchus my kiss formerly Salmo gairdneri. This species represents one of the most highly prized game fishes in North America. The names rainbow and kamloops trout refer to the nonanadromous populations of this species, while the steelhead is normally used to refer to the large, anadromous variety of this species. The kamloops trout usually refers to the larger variety of the nonanadromous trout. All varieties of this species are highly prized sport fishes. The flesh is red to pink in fish that have been feeding on planktonic organisms and it tends to be more pale in fish from larger lakes where they feed on fish more than plankton. They take the bait or lure aggressively and fight the line, jumping out of the water many times in the process.

Most of the steelhead are caught in fresh water in coastal areas. The commercial catch is usually incidental to the salmon fishery and are almost exclusively canned. The commercial gear involved in this fishery, therefore, consists of gill nets.

Although the native range of this species is the eastern Pacific Ocean and for the freshwater forms, west of the Rocky Mountains from Mexico to Alaska, all forms of the rainbow trout can be found throughout North America in suitable habitats. It has also been introduced successfully in New Zealand, Australia, Tasmania, South America, Africa, Japan, southern Asia, Europe, and Hawaii. It is a very plastic species that adapts to different environments readily and may show variations in its physical and behavioral characteristics throughout its range. It is probably the most studied fish in terms of fish physiology and anatomy.

The nonanadromous rainbow and kamloops trout are naturally spring spawners. They move from the lakes to inlet or outlet streams from about mid-April to June and spawn in streams with beds of fine gravel. This is the timing for North America. Because their distribution spans the globe, the actual month of spawning will depend on when spring occurs at a particular location. The fecundity is about 1,400-2,700 eggs, but this is extremely variable; the range extends from 200 to 12,750. The eggs are 3-5 mm in diameter. The eggs usually hatch in about four to seven weeks and the yolk is consumed in about three to seven days. The young emerge from the gravel between mid June and mid August and may reside in the stream until fall of that year or they may spend as long as three years in the stream. The young of the rainbow and kamloops trout will then migrate upstream or downstream to the lake to feed and mature until they are ready to spawn.

The anadromous steelhead trout populations may spawn in the spring, fall or winter. An established population for a given stream, however, will maintain a consistent pattern from year to year. The fecundity and egg size are similar to the rainbow and kamloops trouts. Most of the young will spend two to three years in fresh water before migrating to sea as smolts in the spring, where they may spend an equal amount of time maturing in the ocean. Many will survive the spawning and return for a second or third spawning.

Atlantic Salmon

The Atlantic salmon (Salmo salar) has attracted both commercial and sport fisherman like no other species throughout history; so much so that populations of Atlantic salmon disappeared from the Thames in 1833 and from Lake Ontario in 1890 due to overexploitation. The Atlantic salmon are caught commercially with net and troll gear. They are caught in the sport fishery with live bait as well as on the fly and artificial lures. The intensive interest on this species has, unfortunately, eliminated entire populations of this species from certain watersheds over time. The commercial fishery for the Atlantic salmon off Greenland places a particularly heavy pressure on the Atlantic salmon population at large, because those waters represent the major feeding grounds for all the stocks in the Atlantic Ocean.

The native distribution of the Atlantic salmon is the basin of the North Atlantic Ocean, from the Arctic Circle to Portugal and from northern Quebec south to the Connecticut River. While fertilized eggs and live fish transplantations to the Pacific waters have occurred since 1905, there is no record of the establishment of self-sustaining populations. Like several of the Pacific salmons, there are established landlocked populations of this species in North America. The landlocked Atlantic salmon are sometimes called the ouananiche. There are self-sustaining populations in Sebago Lake, Maine; Lake Ontario; and Lake St. John, Quebec.

The Atlantic salmon is a typical anadromous fish. They spend 1-3 yr in fresh water as juveniles and migrate to sea as smolts where they may spend 1-2 yr growing and maturing. While mortalities in spawning are high, significant numbers of spawners return to spawn two or three times. The normal spawning time is from October to late November. The fish in the southern regions tend to spawn later. The female will produce about 1,540 eggs per kg body weight. The size of returning adults ranges from 2.7 to 6.8 kg. The returning adult spawner will normally have spent 2 yr at sea. The Atlantic salmon generally have longer life spans than the Pacific salmon. Ages up to 11 yr have been reported. While the eggs may hatch in April of the following year, the young alevins will stay in the gravel and consume their yolk until May or June, at which time they emerge into the water column. The period of freshwater residence is variable, depending on the location. The younger parr in North America will spend 2-3 yr in fresh water until they smolt, at about 15.2 cm in length. Populations in Greenland, however, have been recorded to spend as long as 4-8 yr in fresh water, attaining about the same body size.

Unlike the slow growth in fresh water, the Atlantic salmon undergo rapid growth at sea. An exception to the average size of returning adults, stated above, are the precociously matured fish that return after one year at sea. These are often males and are in the 1.4-2.7 kg range. There are many reports of individuals exceeding the normal size range. While the average Atlantic salmon caught commercially is about 4.6 kg, record sizes of 35.9 and 37.7 kg have been reported. While the average landlocked Atlantic salmon weighs about 0.9-1.8 kg, individual fish weighing 16.1 and 20.3 kg have been caught in North American lakes.

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