Chinook Salmon – Oncorhynchus tshawytscha
Spawning Phase – freshwater
Ocean Phase – saltwater
Adult: In the ocean the colour patterns of Chinook and Coho are quite similar – both having dark spots on their backs and tails. However, in comparison to Coho, Chinook have spots on both the upper and lower lobes of the caudal fin (tail). Chinook also have black gums at the base of the lower jaw. Spawning adults darken as they mature and may exhibit a dull brassy sheen or rose colour along the midlateral flanks.
Fry: Parr marks are roughly bisected by the lateral line. The leading edge of the dorsal fin is dark and the adipose fin has a clear centre.
In British Columbia Chinook inhabit medium to large rivers along the coast. In the Skeena River, Chinook ascend as far as the headwaters.
Chinook spawn in over 250 rivers and stream across British Columbia. There are two life-history traits in Chinook salmon: 1. Ocean-type Chinook that migrate to the ocean in their first year, and 2. Stream-type Chinook that migrate to the ocean after 1 to 2 years in freshwater. Entry to freshwater varies with their geographic range. Northern populations enter freshwater as early as April, however peak migration is in June. In comparison to other Pacific Salmon, Chinook typically spawn in larger streams with higher velocity, over coarser substrate. However, they will also spawn in small (2-3m wide) shallow streams, and mainstems or side channels of large rivers. As with other salmonines the female selects a spawning site with preference to subgravel flow. A large dominant male will accompany the digging female however, smaller males and jacks are not far away.
Eggs incubate over winter and alevins emerge in the spring. As with other salmonines, the rate of development is temperature dependent. Depending on water temperatures eggs hatching may occur after 34 – 132 days and emergence of the alevins after 61 – 220 days.
Age, Growth, and Maturity
Ocean-type Chinook fry grow faster in their first year than stream-type fry. Ocean-type fry range between 44 – 98 mm. Fry range between 43 – 93 mm in their first year in freshwater and yearling smolts range from 45 -110mm. After migrating to saltwater Chinook grow rapidly reaching lengths up to 420mm by age 2. Mature males return to freshwater in their second or third year where as females return in their third or fourth year. Depending on the life-history, Chinook returning to spawn are between 2 to 5 years old.
In estuaries Chinook fry feed on chironomid larvae and pupae, cladocerans, amphipods, crab larvae, harpacticoid copepods and possum shrimp. Off-shore in the ocean juvenile Chinook begin feeding on small fish (chum salmon fry, herring larvae, smelts, and other fish). In freshwater Chinook fry feed on adult chironomids as well as chironomid larvae and pupae, terrestrial insects taken from the surface, and the nymphs and larvae of aquatic insects. The diet of juvenile Chinook in freshwater is dependant on the various life stages of terrestrial and aquatic insects. Primary prey varies among sites but cladocerans, chironomids, and plecopterans are typically main components in their diet. In the ocean both adult and juvenile Chinook feed heavily on fish (herring, anchovies, sand lance, and pilchards).
McPhail, J.D. (2007). The Freshwater Fishes of British Columbia. Edmonton, Alberta: The University of Alberta Press.