Oncorhynchus tshawytscha
chinook salmon

Chinook Salmon are found natively in the Pacific from Monterey Bay, California to the Chukchi Sea, Alaska in North America and from the Anadyr River, Siberia to Hokkaido, Japan in Asia. It has also been introduced to many places around the world including the Great Lakes and New Zealand. (Delehay and ADFG, 1994; Matthews and Waples, 1991; NOAA, 2002; Pacific States Marine Fisheries Commision, 1996; University of Wisconsin Sea Grant Institute, 2002)

The Chinook Salmon is anadromous– born in freshwater, migrating to the ocean, and returning as mature adults to their natal streams to spawn. Freshwater streams, estuaries, and the open ocean are all important habitats. The freshwater streams are relatively deep with course gravel. The water must be cool, under 14 C for maximum survival, and fast flowing. Estuaries provide a transition zone between the freshwater and saltwater and the more vegetation the better because there will be more feeding and hiding opportunities. At sea, Chinook Salmon can either stay close to shore or migrate thousands of miles to deep in the Pacific. (National Wildlife Federation, 1996-2002; NOAA, 2002; Pacific States Marine Fisheries Commision, 1996)

The Chinook Salmon is the largest of all Pacific salmon species, often larger than 100 lbs and longer than 5 ft. It is characterized by a deep blue-green back, silvery sides and a white belly with black irregular spots on the back, dorsal fin and both lobes of the tail. It also has a small eye, black gum coloration, a thick caudal peduncle and 13-19 anal rays. For spawning, both males and females develop a reddish hue on the sides, although males may be deeper in color. Males can also be distinguished by a hooked nose and a ridged back. The Chinook fry look very different, with well developed parr marks (vertical bars) on their sides. (Delehay and ADFG, 1994; Government of Canada, 2002; National Wildlife Federation, 1996-2002; NOAA, 2001; Pacific States Marine Fisheries Commision, 1996)

The female digs a nest (called a redd) in the gravel and then deposits her eggs and the male deposits sperm. After 90-150 days (depending on temperature) the eggs hatch, and the alevins (fry with yolksacs attached to the underside) stay in the gravel until the yolksac is used up. The fry then emerge from the gravel in the spring and feed and grow for a few months to two years, depending on the stream system. They then migrate downstream as smolts, following the natural current. The smolts undergo huge physiological changes in their transition from freshwater to salt water. They then spend the next 1-7 years growing and maturing at sea. Growth rates in the ocean are much faster, and perhaps as much as 99% of the somatic growth occurs as sea. Mature adults will then return to their natal streams to spawn. Once the adults have re-entered freshwater, they no longer feed, and they complete sexual maturation during the freshwater migration (Pacific States Marine Fisheries Commission, 1996; National Wildlife Federation, 2002; NOAA, 2001; Delaney and ADFG, 1994; University of California at Berkeley; Government of Canada, 2002; Ewing and Ewing, 2002; Satterfield and Finney, 2002).

The average age of spawning adults is 4-6 years, however, they can spend up to 8 years in the ocean or return after less than one year. The average age is slightly younger in the south with 2/3/4 year-olds most common; 5/6/7 year-olds are most common in the north. Often, females are older than males at sexual maturity. There is high mortality early because of high natural predation, and those smolts that do not reach a certain size before their first winter at sea will not survive colder temperatures. Human modification of the environment has led to even higher mortality, mainly due to siltation and decreased water flow which have reduced the availability of oxygen to the eggs and fry (Pacific States Marine Fisheries Commission, 1996; Delaney and ADFG, 1994; Government of Canada, 2002).

Chinook Salmon are anadromous, making great migrations out to the deepest parts of the ocean and returning as mature adults to their natal streams. In order to return to the exact right stream, they use sun-compass orientation out in the open ocean and then smell to get them to the right stream. All adults return at the same time, spawn so that all fry will emerge at the same time, and then all smolts migrate downstream at the same time.

There are two basic behavior types, stream-type and ocean-type, which depend on the amount of time juveniles spend in freshwater. The stream-types spend 1-2 years in the stream, and are therefore much more dependant on the stream ecosystem than are the ocean-types, which migrate to the ocean in less than 3 months. Stream-types are mostly found in the north, and have chosen more stable streams with consistently high productivity and relatively little change in water flow. Stream-types also usually migrate very far into the ocean whereas ocean-types generally stay close to the coast, migrating north instead. The ocean-types developed in areas with lower carrying capacities or high seasonal flooding. Stream-types deposit a significantly lower number of eggs, and typically these eggs are smaller because their long freshwater migration takes so much energy while they are not feeding, so they have little left to invest in their gametes (Pacific States Marine Fisheries Commission, 1996; Matthews and Waples, 1991; NOAA, 2001; University of Wisconsin Sea Grant Institute, 2002; Healey, 2001).

External fertilization in Chinook Salmon requires precise communication in order to ensure proper timing of gamete release. During the courtship, which can last up to several hours, the male vibrates and crosses in front of the female, while the female is preparing for spawning by digging the redd. The female has been shown to selectively choose larger males, who vibrate more. A few seconds before depositing her eggs, the female will shake quickly next to the male, inducing sperm release (Berejikian, Tezak, and LaRae, 2001).

While in freshwater, Chinook Salmon fry and smolts feed on plankton and then terrestrial and aquatic insects, amphipods and crustaceans. After migrating to the ocean, the maturing adults feed on large zooplakton, herring, pilchard, sandlance and other fishes, squid, and crustaceans. Once the adult salmon have re-entered freshwater, they do not feed. In the Great Lakes, Chinook Salmon were introduced to control the invasive alewife population (National Wildlife Federation, 2002; Delaney and ADFG, 1994; Government of Canada, 2002).

For young Chinook Salmon, predation is very high. Many species eat the fry and smolts, including striped bass, American shad, sculpins and sea gulls. Reaching adulthood does not release them from predation, however, as they are still prey to many animals when they return to spawn. Most common are bears, orcas, sea lions, seals, otters, eagles, terns and cormorants. People have made predation worse by concentrating adult salmon at dams and weirs (Pacific States Marine Fisheries Commission, 1996; National Wildlife Federation, 2002; NOAA, 2001; University of California at Berkeley).

Spawning Chinook Salmon are the keystone species in many streams because so many other species rely on them for food. In the ocean, they are often one of the top predators. Chinook Salmon are now the top predator in the Great Lakes where they were introduced to control other non-native fish species (University of Wisconsin Sea Grant Institute, 2002).

The Chinook Salmon is very important to commercial, recreational, and subsistence fishermen. It has always been central to the Native American lifestyle on the Pacific coast, and now much of the economy of the Pacific Northwest is based on it. Despite being relatively rare (compared to other Pacific Salmon species) it is the most commercially valuable. It is also now an important big game fish in the Great Lakes and is a big tourist draw in both the Pacific and Great Lakes regions

(Pacific States Marine Fisheries Commission, 1996; National Wildlife Federation, 2002; Delaney and ADFG, 1994; University of Wisconsin Sea Grant Institute, 2002).

The Chinook Salmon has 17 distinct Evolutionarily Significant Units, (ESU) in the US only, two of which are endangered and seven of which are threatened.

ENDANGERED:

Sacramento River Winter Run,

Upper Columbia River Spring Run

THREATENED:

Snake River Fall Run,

Snake River Spring/Summer Run,

Central Valley Spring Run,

California Coastal,

Puget Sound,

Lower Columbia,

Upper Willamette,

CANDIDATE:

Central Valley Fall Run

NOT WARRANTED:

S. Oregon/N. California Coastal,

Upper Klamath Trinity,

Oregon Coastal,

Washington Coastal,

Mid Columbia Spring Run,

Upper Columbia Summer/Fall Run,

Deschules Summer/Fall Run

Many agencies have been set up to protect this species, including the Pacific Fisheries Management Council, the North Pacific Fisheries Management Council, and the National Marine Fisheries Service. The federal Magnuson-Stevens Act was made to protect the Essential Fish Habitat, the waters and substrates necessary to fish for spawning, breeding, feeding and growing to maturity. The Sustainable Fisheries Act has amended the Magnuson-Stevens Act.

The main causes for the declining fish populations are overfishing, damming and diverting water, habitat destruction, and introducing hatchery populations. Overfishing has decreased population sizes enough that all other causes, along with natural predation, can have extreme effects, and population sizes decrease rapidly. Damming causes decline because it blocks adults from returning to their birthplace and because smolts often get sucked into the turbines of hydroelectric dams and are killed. Diverting water away from salmon streams causes water temperature to rise, reducing the oxygen carrying capacity of the water. Temperatures could also become fatally high in the summer. Reduced water levels could expose eggs in the winter, or flows could be too low to carry smolts out to sea. Habitat destruction, including logging, clearing rivers, pollution, and wetlands destruction, take away shade and necessary protection for juveniles. After logging has changed runoff patterns, streams may contain too much silt and become uninhabitable. Pollution can cause many physiological problems, including increased susceptibiity to pathogens. Introducing hatchery populations adds to the decline because the introduced populations interbreed with the native populations and can reduce resistence to disease (Pacific States Marine Fisheries Commission, 1996; National Wildlife Federation, 2002; NOAA, 2001; University of Wisconsin Sea Grant Institute, 2002; Arkoosh and Collier, 2002).

Chinook Salmon population sizes have been shown to fluctuate with long-term climate changes. The most dramatic example of this is the El Nino events, every 3-7 years, which bring warm water into the Pacific and negatively affect Chinook Salmon populations. Longer term changes have involved changes in water currents over time, which have had opposite effects in Alaska and along the coast of California. In Alaska, these changes have caused a change in the mixing layer which has increased the chlorophyll levels in plankton, making the system more productive. This has increased the zooplankton population, which in turn causes an increase in the salmon population size. In California, however, climatic changes have caused the mixing layer to deepen, which has reduced the amount of nutrients available, causing the salmon population to decrease (Taylor and Southards, 1997; Satterfield and Finney, 2002; Botsford and Lawrence, 2002; Dalton, 2001).