Marine Science Chapters


Salmon Species Diversity

North Pacific Salmon Species Ranges

There are five species of North Pacific native salmon in the genus Oncorhynchus. These species are commonly called the Chinook, coho, pink, chum and sockeye. They are all considered to be anadromous, meaning that they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. They may travel thousands of miles in the ocean and are able to return to their natal stream by the use of sensing Earth's magnetic fields (like migrating birds) to find their way. Then they use their acute sense of smell to swim upstream - taking each fork as it comes - to the place where they hatched. All the North Pacific salmon die after spawning - providing food for predators or decomposing to release their nutrients into the stream or surrounding terrestrial area. (NASA image edited by GA above)

Salmon body form
Salmon body form. (GA image)

Salmon have a standard fish body form. Like most fish they have a mouth, pair of eyes and a pair of nostrils (nares) in their head. Most fish, including salmon, also have three midline fins (dorsal, caudal, and anal) as well as two types of paired fins (pectoral and pelvic).

Salmon fin with soft supports Salmon adipose dorsal fin
Salmon fin showing supports as all soft rays (no spines) (left). Salmon adipose dorsal fin (right) has no fin supports, just flesh. (GA images)

Salmon pelvic fin with axillary process
Salmon pelvic fin pulled out to show axillary process. (GA image)

Salmon have three obvious unique characteristics that can be used to separate them from other fish anatomically. These are as follows: (1) all of their fins are supported by soft fin rays (no spines), (2) their second dorsal fin is an adipose (fleshy) fin and lacks any fin supports and (3) they have an axillary process (a small bump on their body) where each pelvic fin joins the body.

Salmon skin with overlapping scales Salmon scale showing growth rings
Salmon skin showing overlapping scales (left). One salmon scale close up showing growth rings (right). (GA images)

Salmon skin is covered with protective scales, secreted by the epidermal (skin) cells. Salmon scales are all cycloid, with concentric rings. These rings can be counted for age.

Salmon gills
Salmon gills. (GA image)

Salmon gill arches One salmon gill arch
Salmon gill arches (left) under gill cover. One salmon gill arch (right) showing gill rakers along the white arch. (GA images)

Salmon gill rakers
Salmon gill rakers close up (the white, hard, spiny projections) used to catch plankton by some salmon (above). (GA image)

Salmon all have gills, for oxygen and carbon dioxide exchange. Water enters the mouth, flows across the gills in the back of the throat, and out the gill slit on each side of the body. Gill rakers, on their gills, are used to strain plankton from the water in some species. Each gill slit is supported by a bony operculum as is present in most bony fish. [The sharks and the rays also have gill slits but they usually have 5-7 pair on each side and none are supported by bone.]

Salmon head with eye, mouth, and nostrils (nares)
Salmon head with eye, mouth and nostrils (nares) (above) - from a restaurant so it is probably an Atlantic farm raised species. (GA image)

Salmon have excellent vision. They can see both in front of their bodies and to the sides. Salmon can also see colors and are good at judging distances both in and out of the water. The have been known to jump out of the water to catch a flying dragonfly out of the air. This means that they have the ability to interpret how light bends when entering the water and account for this when they aim for airborne prey. Salmon are also known to be able to see terrestrial predators from under the water and swim for cover. It is thought that they have the ability to focus both at close range and far away as well has have the ability to see and interpret movement.

Salmon stream
Salmon stream. (GA image)

Salmon are unique in being anadromous. Salmon are considered the classic example of an anadromous fish (beginning life in fresh water, migrating to the ocean and returning to fresh water to reproduce). Migration to the ocean allows these fish to grow a lot larger than would be possible in fresh water because the ocean has so much more food. Larger fish can dominate reproductive areas and lay more eggs than smaller fish resulting in evolutionary advantages for the long migrations of the salmon. [There are also catadromous fish - those that begin life in the ocean, migrate to fresh water to grow up, and then return to the ocean for reproduction. These fish are not well known and are generally represented by the Atlantic yellow eel (Anguilla).]

The scientific species names of the North Pacific salmon were taken from the notes of an early naturalist, George Steller, about 1740. He was one of the first to write about the North Pacific salmon. He wrote about the natural history of the Kamchatka Peninsula in Russia. In his notes he referred to each of the five North Pacific salmon species by the names that the native peoples (the Koryak) used. Later these names were translated, Latinized and used as species names.

North Pacific Salmon
(listed by size from smallest to largest)

Common Name Scientific Name Other common names Adult Length Adult Weight Life Span

Pink Salmon Oncorhynchus
humpback, humpy 18-24 inches 3-5.5 pounds 2-3 years

Sockeye Salmon Oncorhynchus
redfish, red, blueback 21-26 4-7 pounds 4-6 years

Coho Salmon Oncorhynchus
silver, silverside 24-28 inches 6-9.5 pounds 2-4 years

Chum Salmon Oncorhynchus
dog, calico 24-31 inches 6.5-12.5 pounds 3-5 years

Chinook Salmon Oncorhynchus
king, tyee, quannat 28-40 inches 10-25 pounds 3-6 years

The information in the above table and species diversity notes is summarized from one of the finest books on salmon. This reference is highly recommended as a source for factual information as well as wonderful drawings (by Joseph R. Tomelleri) of each species of salmon (and trout). The book is by Robert J. Behnke, entitled Trout and Salmon of North America, published in 2002 by The Free Press, New York.

Pink Salmon, saltwater form Pink Salmon, freshwater form of reproductive male
Pink salmon, ocean form (left) and freshwater form of reproductive male (right). (LFJ images)

Pink Salmon
Pink Salmon. (GA image)

Pink salmon are the most abundant of the five North Pacific salmon species although they are the smallest. Because of their abundance they are one of the most important in the salmon fishery. The pinks are not considered to be one of the finest eating salmon however, because their flesh has a low fat content and is on the pale side.

Pink salmon first entering stream Pink salmon male with hump
Pink salmon first entering a stream (left). Male pink salmon after developing hump in fresh water (right). (GA images)

Most pinks reproduce at two years (with only a few reproducing at three years in the coldest areas). This results in two distinct types of pink salmon - even year classes and odd year classes. Rarely do these two groups mix during reproduction. This species spends the least time in fresh water of all the North Pacific salmon (less than six months as babies). They generally spawn close to the mouth of their stream with little, or no, upstream migration.

Sockeye Salmon, saltwater form Sockeye Salmon, freshwater form of reproductive male
Sockeye salmon, ocean form (left) and freshwater form of reproductive male (right). (LJF images)

Sockeye Salmon, reproductive form, NOAA image
Reproductive form (freshwater) from stream. (NOAA image)

Sockeye salmon are the most important commercial species of North Pacific salmon. This is because they have oil-rich flesh that is a deep orange/red in color. This species is on the smallish size (only pinks are smaller) and when it is in the ocean it feeds primarily on plankton. This species has more gill rakers than other salmon to facilitate this plankton feeding.

Sockeye salmon in stream
Sockeye salmon in stream. (GA image)

The greatest diversity in life history details is found in the sockeye salmon. Baby sockeye may spend three months to three years in fresh water. Adults may spawn near shorelines, on lake bottoms, or hundreds of miles upstream. Some populations spawn within weeks of entering fresh water and others take months.

Coho Salmon, saltwater form Coho Salmon, freshwater form of reproductive male
Coho salmon, ocean form (left) and freshwater form of reproductive male (right). (LJF images)

Coho Salmon, NOAA image
Coho Salmon. (NOAA image)

Coho salmon are a favorite sport fish. They feed near shore and are thus near areas where anglers fish. This species is the second least abundant of the North Pacific salmon (Chinook are the least abundant). Coho salmon make up only seven to ten percent of the commercial salmon fishery.

Young coho spend one or two years in fresh water. Salmon in the southern part of their range (warmer) spend one year and salmon in the northern part of their range (cooler) spend two years. This species usually goes less than one hundred miles from the mouth of their stream for reproduction although a few populations travel over a thousand miles - so there is quite a diversity in this species.

Chum Salmon, saltwater form Chum Salmon, freshwater form of reproductive male
Chum salmon, ocean form (left) and freshwater form of reproductive male (right). (LJF images)

Chum Salmon, NOAA image
Chum Salmon. (NOAA image)

Chum salmon are the most widely distributed and have the greatest biomass of the North Pacific salmon. They are the second largest of the salmon (Chinook are the largest). Chum salmon are one of the most common salmon in the sport fishery. The name 'chum' comes from a word meaning 'variegated coloration' in the native language and chum salmon have a different coloration (from other salmon species) that is variegated.

Reproduction for chum salmon is somewhat varied. Many reproduce near the mouth of their stream (like pink salmon) whereas others travel up to one hundred miles inland. They migrate to the ocean after six to seven months in fresh water but spend three to five years in the ocean. The long period of time spent in the ocean gives them plenty of time to feed and grow to their large size. Because they are found in the same streams, the chum may hybridize with the pinks in their stream. Although this rare event has been documented numerous times (and the hybrids are thought to be fertile) there are no hybrid populations that are self-sustaining at this time.

Chinook Salmon, saltwater form Chinook Salmon, freshwater form of reproductive male
Chinook salmon, ocean form (left) and freshwater form of reproductive male (right). (LJF images)

Chinook Salmon, NOAA image
Chinook Salmon. (NOAA image)

Chinook salmon are the largest, but least abundant of the North Pacific salmon. Because of their low abundance they are of minor importance in the salmon fishery. The name 'Chinook' came from the native peoples of the Columbia River (Washington and Oregon) and thus is a proper name and always capitalized.

Young Chinook spend one to two years in fresh water. Like coho, it is the populations in the southern part of their range that migrate to the ocean after one year and it is the populations in the northern part of their range that migrate to the ocean after two years. Many Chinook migrate over two thousand miles downstream as babies and then upstream as adults. It is believed that there are now only five to ten percent of the Chinook salmon left that were here only 150 years ago.

There are two more salmon species in the northern hemisphere - one in the waters of northern Asia and one in the North Atlantic. The salmon from Asia is called the cherry (or masu) salmon and is classified in the genus Oncorhynchus as are the five common North Pacific salmon just described. The North Atlantic species is classified in the genus Salmo and is different in several ways. One of the major differences is behavioral as the Atlantic salmon can spawn up to three times in its life, returning to the ocean in between whereas none of the Pacific salmon can do this.

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(Revised 21 March 2010)
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