Salmon

Introduction to Salmon

Salmon, a valuable food and game fish. Salmon are normally found in temperate or Arctic waters of the Northern Hemisphere. There are seven species of salmon—one found in the Atlantic Ocean and six in the Pacific.

Most salmon are anadromous—that is, the adults migrate into freshwater rivers or lakes to breed. Salmon are famous for the runs they make as they return to their place of birth to spawn. Leaping high into the air to surmount obstacles, the fish fight their way upstream to the headwaters of their native rivers. It is at this time, when the fish are in prime condition, that the catch is taken by sport and commercial fishermen. (For record catches, table of freshwater fishing records.)

A salmon is a bony fish because its skeleton is made mostly of bone. The skull, backbone, and ribs are made of bone. Salmon and most other bony fish also have many thin bones, called rays, inside their fins.

Skull bones form the frame for a salmon’s head. The skull bones include the upper and lower jaw and the brain case. Bony plates protect the gills that are located on the side of a salmon’s head.

The backbone forms the frame for the rest of a salmon’s body. The backbone has many separate pieces of bone called vertebrae (VUR tuh bree). The ribs are attached to the vertebrae.

Bony fin rays form the frame for a salmon’s fins. Fins help the fish swim and keep its balance.

Fish are vertebrates (VUR tuh brihts), which are animals with backbones. Fish live in water and usually breathe with gills. A bony fish is a fish whose skeleton is made mostly of bone. Salmon and trout are bony fish. Bass, catfish, flounder, barracuda (bair uh KOO duh), and seahorses are bony fish, too.

Altogether, there are about 24,600 kinds of fish. Most of these fish have bones. In fact, there are about 23,700 kinds of bony fish. But some fish, including sharks and their relatives, have no bones at all. Instead they have skeletons made of a tough, rubbery material called cartilage (KAHR tuh lihj).

Bony fish live almost anywhere there is water. They are found in chilly waters in the Arctic and in warm waters in the tropics. Bony fish swim in streams, rivers, lakes, and oceans. Salmon are bony fish that usually grow up in streams, but they spend their adult lives in the ocean.

Most adult salmon live along the coast of the North Pacific Ocean. These include the chinook (chuh NOOK), chum, coho, pink, and sockeye salmon. Amago and cherry salmon are found in the Pacific waters of eastern Asia. Only one kind of salmon, the Atlantic salmon, swims in the Atlantic Ocean.

A few groups of salmon live their entire lives in northern lakes and streams that don’t flow to the ocean. People have released freshwater salmon into other lakes around the world. There they have become popular sport fish.

Adult salmon are shaped a bit like torpedoes so that they can easily dart through the water. An adult salmon has six kinds of fins. The smallest fin is called the adipose (AD uh pohs) fin. It’s located on top of the body, near the caudal (KAW duhl) fin.

Hard, shiny scales cover the salmon’s skin and protect its body. Most adult salmon found in the ocean have dark-colored backs and silvery-white bellies.

Typical salmon grow to a length of about 2 feet (61 centimeters) and weigh about 10 pounds (4.5 kilograms). But chinook salmon can grow much bigger. Chinook salmon can reach 3 feet (91 centimeters) long and weigh over 100 pounds (45 kilograms). That’s why chinook salmon are also known as king salmon.

Atlantic Salmon

The Atlantic salmon is found on both sides of the North Atlantic as far north as the Arctic Circle. The adult is blue-black above with silvery sides. During the long journey to spawn, the male becomes dirty red on the sides and develops a hook-shaped lower jaw. The sides of the female become black. The adult fish ordinarily is 2 to 4 feet (60 to 120 cm) long and averages 8 to 12 pounds (3.6 to 5.4 kg).

At one time this fish was plentiful in North America as far south as the Hudson River, but the principal fisheries are now in Canada. Atlantic salmon are also found in a few freshwater lakes, where they remain throughout their lives. These fish are called landlocked salmon. They are caught as game fish in Maine, New York, New Hampshire, and the Maritime Provinces of Canada.

Pacific Salmon

Five species of Pacific salmon are found in North American waters, from Alaska to southern California. They are the chinook salmon (also called king, or spring, salmon); the sockeye, or red, salmon; the coho, or silver, salmon; the chum salmon (also called dog, or keta, salmon); and the pink, or humpback, salmon.

Chinook and coho are the most important sport species. Commercially the pink salmon holds first place in quantity caught, the sockeye in value of the catch. A few populations of certain species of Pacific salmon are landlocked, spending their entire lives in freshwater.

Pacific salmon are silvery with bluish backs that are spotted with black. As the fish mature and reach spawning time, their color changes to shades of red, yellow, or black, depending on species and sex. The males also develop a hook at the tip of both jaws.

The chinook salmon is the largest of the Pacific species, weighing about 20 to 25 pounds (9 to 11.3 kg). An average mature fish is about 4 feet (120 cm) long. The flesh is red, pink, or white.

The sockeye salmon weighs about 5 pounds (2.3 kg) and is about 2 feet (60 cm) long. It is highly prized for its firm, red flesh and excellent flavor.

The chum salmon usually weighs 8 to 18 pounds (3.6 to 8.2 kg) and reaches a length of 3 feet (90 cm). The flesh is whitish.

The pink salmon is the smallest of the Pacific species. It weighs about 3 to 5 pounds (1.4 to 2.3 kg) and is about 2 feet (60 cm) long. The flesh is pink. An unusual feature of the pink salmon is that on its way to spawn the male develops a large hump on its back.

The coho salmon attains a length of about 3 feet (90 cm) and usually weighs 6 to 15 pounds (2.7 to 6.8 kg). The flesh ranges from pink to red.

Spawning

Salmon that survive to maturity in the oceans return to the freshwater river of their origin to spawn, although some may stray to other streams. Scientists cannot fully explain why salmon are able to return to their native rivers to spawn, but it is known that in the final stages of their migration, the fish are guided largely by their sense of smell.

The migration to the spawning grounds begins at the same time for all the salmon in any one population. Depending on the particular population, the migration may begin any time from May to December, and spawning takes place from about June to January. The trip may be 200 miles (320 km) or more upstream. At the start of the run the fish are in prime condition; during the migration they eat nothing.

Once the spawning grounds are reached, the female, by using her tail, makes a nest (called a redd)in the gravel. She deposits her eggs, and the male releases sperm to fertilize the eggs. Salmon lay several thousand eggs. After spawning, the adults of the Pacific species die. Adult Atlantic salmon slowly make their way downstream to reenter the sea. The Atlantic salmon may spawn several times before dying.

The eggs hatch the following spring. Attached to the underside of a baby salmon (called an alevin or fry)is a yolk sac that will nourish the young fish for a few weeks. After the food material in the yolk sac is used up, the fish is called a parr or fingerling. At this time the young fish may immediately make its way to saltwater, or it may remain in freshwater for up to four years, depending on the habits of its population. At all times, salmon are prey to other animals, and only a small percentage of them live to reach the ocean. The salmon remain in the ocean from two to eight years before they are ready to spawn.

Most adult salmon live in the salty ocean. In the summer and fall, however, they swim up a freshwater stream to spawn, or mate. That’s where the females lay their eggs.

Soon after the adult salmon arrive, the female digs a redd, or nest. She does this by slapping her tail hard on the gravel bottom. When the redd is finished, the female lays her round, pink eggs. As the eggs are laid, a male fertilizes them.

After the redd is filled with fertilized eggs, the female swims a little farther and digs a new redd. As she digs, she stirs up gravel with her tail. The current carries the gravel over the old redd. There the gravel settles and protects the eggs. Altogether, a female salmon may lay between 2,000 and 17,000 eggs, depending on her size.

Baby salmon first grow inside eggs. They use the yellow-orange yolks in the eggs as food. After two to four months, the babies hatch out of the eggs.

After hatching, the baby salmon are called alevins (AL uh vihnz). They stay in their nests for several weeks or months. During this time, these tiny salmon still have yolk sacs attached to their bodies that supply them with food.

While in the nest, an alevin smells the water around it. Specific rocks, plants, and chemicals in the stream give the water its smell. And no other stream has the exact same smell. An alevin remembers this smell and never forgets it. When it is an adult, a salmon uses the smell to return to the exact same stream to spawn.

A salmon fry sounds like a fish dinner, but it’s actually the name for a young salmon. By the spring, a baby salmon is big enough to leave its nest. When it is ready to do this, it is called a fry. A fry is about 1 inch (2.5 centimeters) long.

The yolk sac that had fed the alevin until this point is gone. Now the fry must start to look for food. It eats insects and small water organisms called plankton. Fry must be careful because trout and other big fish eat them. Hungry ducks, herons, kingfishers, and sea gulls do, too. The fry starts to grow scales on its skin to protect its body. Most salmon fry also develop spots called parr marks. These spots help fry hide in the rocky stream. Even so, many of them are caught and eaten.

The fry of some kinds of salmon stay in fresh water for only a few days. Then they start their long swim to the salty ocean. The fry of other kinds of salmon stay in fresh water much longer before heading to the ocean.

A salmon becomes a smolt when it swims from its freshwater stream and heads to the ocean.

A smolt’s body goes through many changes as it makes this journey. It loses its parr marks. It turns dark on top and silvery-white on its sides and belly. Its new colors help the smolt hide in the ocean. From above, a smolt’s dark top will be hard to see against the deep blue waters of the ocean. And from below, a smolt’s silvery-white belly will be hard to see against light shining down through the water.

Changes also take place inside the young salmon. Its kidneys and gills become very good at getting rid of large amounts of salt. This will come in handy in the smolt’s new ocean home. Many smolt actually wait at or near the mouths of streams or rivers for several months. This water is less salty than water farther out in the ocean. Waiting here gives a smolt’s body time to get used to the change.

When adult salmon are ready to spawn, they return to their home streams. Salmon use their sense of smell to help guide them back to the same stream where they hatched.

On their journey home, adult salmon make many changes—much as they did on their first trip to the ocean. Most salmon change color to attract a mate. Adult chinook salmon turn from silvery-white to brownish-red. Sockeye salmon turn from silver to bright red. Most salmon also stop eating and focus on their journey.

The trip home is very hard. It can take several weeks, and it can cover 2,000 miles (3,200 kilometers). The salmon must swim upstream, against the water current. They leap high over big rocks and waterfalls. Some become weak or get injured and die along the way. For most kinds of salmon, even those that survive the trip die after they spawn.

Commercial Fisheries

Most of the commercial catch is made at or near the mouths of rivers as the fish approach the coast. The fish are generally caught with gill nets or purse seines, or by trolling. Most of the Atlantic salmon catch is marketed fresh or frozen; small quantities are canned, pickled, or smoked. About half of the Pacific catch is canned. In modern canneries, nearly all the salmon are cleaned and canned by machinery. In some smaller canneries the cutting and several other operations are done by hand. Some floating canneries are also in operation. Salmon eggs are used to make red caviar. They are also used for bait.

Salmon are among the most valuable fish caught, although the size of the catch by weight is relatively small. They are used almost exclusively for human food, and much of the world catch is canned or otherwise processed. The Atlantic salmon normally provides 8 to 16 per cent of the total world salmon catch, with Norway, Great Britain, Denmark, and Canada the leading nations. The Pacific salmon catch is taken by the United States, Japan, Russia, and Canada.

Overfishing and water pollution have caused a decrease in the number of salmon. In addition, dams, particularly hydroelectric dams on the Columbia and Snake rivers, block salmon from upstream spawning grounds. Many young salmon are killed in turbines at hydroelectric plants. A number of conservation measures are used to protect salmon populations. One of the major conservation measures is the artificial propagation of salmon. Millions of salmon eggs are hatched in hatcheries maintained by state and federal organizations. Fish ladders (series of pools arranged like steps) allow adult salmon to swim upstream over or around dams. At some hydroelectric plants, there are underwater screens that divert young salmon away from turbines and into bypass channels. Despite these and other conservation measures, some species, especially the chinook and the sockeye salmon, continue to decline in numbers.

The closest relatives of salmon are trout. Trout and salmon belong to the same family, or group, of bony fish. They have similar, torpedolike shapes. Both fish have small adipose fins. Some trout and salmon look so much alike that they are often mistaken for each other.

The best-known trout is the rainbow trout. It is closely related to salmon that live in the Pacific Ocean. Like salmon, rainbow trout spawn in streams. Some rainbow trout also travel to the ocean. A rainbow trout that makes this journey is called a steelhead. Most rainbow trout, however, stay in freshwater streams all their lives.

Rainbow trout are named for their colorful reddish bands that run along their sides. These trout also have black spots on their upper bodies and tails. Rainbow trout that stay in streams usually weigh around 2 to 5 pounds (1 to 2.3 kilograms).

Salmon face many dangers. Birds and fish eat salmon eggs, fry, and smolt. Some salmon never get to the ocean because they die along the way. Water pollution is also dangerous for salmon, especially smolt.

A salmon that reaches the sea may be too big for herons or other small birds, but it had better watch out for eagles or ospreys. An adult salmon’s other enemies include bears, sea lions, seals, and killer whales. Many salmon are also caught in large fishing nets.

Salmon that survive in the ocean grow bigger. They eat many sea animals, including shrimp, squid, and other fish. Some kinds of salmon may stay and grow in the ocean for only six months before they return home to spawn. Other kinds may live in the sea for six years or more.

All bony fish, except the largest ones, are always in danger of being eaten by other fish and water animals. Many fish are also in danger of being caught by people.

Salmon is a popular food for people. Each year, fishers from Canada, Norway, Japan, the United States, Chile, and Russia catch millions of salmon. As a result, some types of salmon are now endangered.

To protect the fish, laws now limit salmon fishing in some parts of the world. This allows many salmon to survive in order to spawn. Also, thousands of salmon are now raised in hatcheries and then released into rivers and streams.

Salmon belong to the family Salmonidae. The Atlantic salmon is Salmo salar. It is of the same genus as true trout. Pacific salmon belong to the genus Oncorhynchus. The chinook is O. tshawytscha; the sockeye, O. nerka; the coho, O. kisutck; the pink, O. gorbuscha; the chum, O. keta; the cherry, O. masou.