Coho Salmon – Oncorhynchus kisutch
Spawning Phase – freshwater
Ocean Phase – saltwater
Adults: White gums at the base of the lower jaw teeth. Ocean: Silver flanks and dark spots on the back and tail; spots on tail confined to the upper lobe of the tail only (in comparison to Chinook – having spotting on both lobes). Spawning adults develop red sides and darken as they mature. Male spawning colours are more vibrant than female spawning colours. As with other Salmon, in males the head and teeth on the jaws enlarge, and the end of the snout forms a strong down-turned hook.
Fry: Long narrow lateral parr marks, white leading edges on dorsal and anal fins sharply contrasting with a streak of dark pigment immediately behind the white leading edge. The tail and paired fins often exhibit a pale orange coloration and the anal fin is sickle shaped.
Coho can be found in all large and small rivers along British Columbia’s coast. Most coho populations spawn within 250 km of the ocean. However some Coho populations are known to migrate further (>500km) in larger systems such as the Skeena River.
In British Columbia there are early runs that enter freshwater between September and October and late runs that enter freshwater between December and January. Coho that utilize tributaries of Lakelse for spawning return in early September and spawn as early as October. As with many other salmonines, females choose the spawning site. Coho females prefer a site with subgravel flow such as a tail-out pool immediately above riffles or upwelling sites. Only one dominant 3 yr old male with accompany the digging female; however, smaller 3 yr old males and 2 yr old jacks are array downstream or lurking under cover. In comparison to other Pacific salmon, spawning coho are the most secretive, often conducting reproductive behaviour at night. Coho tend to select stream not much more than 1m wide for spawning with an average substrate diameter of 9.4 cm.
Eggs incubate over winter in the gravel and hatch in the spring. Eggs hatch after 1 -to 4 months and emerge from the gravel after 1 to 3 months depending on water temperatures.
Age, Growth, Maturity
In general coho growth rates are sensitive to temperature, food supply, and fry density. In British Columbia, coho fry usually reach 80-90 mm in their first year. Most young coho spend 1 to 2 years in fresh water before migrating to the ocean. Yearling smolts range from 7 – 12 cm where as 2-yr old smolts range from 10 – 15cm when they migrate. Growth rates increase rapidly in the ocean. Coho typically spend on average 18 months in the ocean before returning to their natal stream to spawn.
Coho fry are primarily drift-feeders. Yearling coho also feed on drifting insects but feed on a wider variety of larvae and nymphs than the fry. Coho juveniles will also feed on terrestrial insects with zooplankton forming only a small part of lake dwelling juveniles. Juveniles become piscivorous (feeding on fish) as they grow and begin migrating to the ocean, feeding heavily on out-migrating pink salmon. Adult coho feed heavily on herring, sand lance, and a wide variety of small fishes and invertebrates. Offshore coho also prey on euphausiids and squid.
McPhail, J.D. (2007). The Freshwater Fishes of British Columbia. Edmonton, Alberta: The University of Alberta Press.