Over the last couple of months we’ve run a couple of really well-received posts from Alaska West guest and fisheries biologist Brian Morrison – on the lifecycles of rainbow trout in Western Alaska, and chinook salmon everywhere.
Today we wrap up the mini-series with some facts from Brian on another favorite of ours, the coho or silver salmon. Thank you, Brian!
Coho Salmon Lifecycles
Coho Salmon (Oncorhynchus kisutch – pronounced “keez-utch”), also called ‘silver salmon’, are considered to be the second most abundant of the five Pacific Salmon species. The average size across their range is much smaller than Chinook Salmon, with adults being approximately 60-80cm long and 6 – 13 pounds, with an unverified record of 46 lbs. Similar to Chinook, Coho will run up short coastal rivers, or large rivers stretching far inland, such as the Yukon River, where adults will travel over 2,250km (1,400 miles) to their spawning grounds. They are also known to travel up streams to over 1,800 meters (6,000 feet) elevation in the Snake River watershed.
Coho Salmon historically ranged from Monterey Bay, California in the south to Port Hope, Alaska, including tributaries along the Aleutian Island chain. Coho’s have also been known to developed residual populations in freshwater lakes connected to the ocean, such as Cultas Lake, British Columbia, although this is a rare occurrence. Coho Salmon have been introduced all across the globe, but have only managed to develop self-sustaining populations within the Great Lakes.
Coho Salmon have less life history diversity when compared to Chinook Salmon. There are seasonal runs, but this is largely related to the latitude of the spawning population, with some exceptions. Spawning will occur during late summer, fall, or early winter.
Juvenile Coho Salmon will spend at least one year, and up to two years in the stream environment prior to smolting. Populations at higher latitudes are more likely to have older smolts (two year olds). After smolting, Coho Salmon can spend anywhere from several months to up to two years in the ocean prior to returning to spawn. Once sexually mature, all adults will die after they spawn. As with Chinook Salmon, male salmon have the greatest breadth in spawning age. They are able to successfully spawn as jacks (one summer in the ocean), or at any age beyond that. Across their range, Coho Salmon generally mature at ages 3 or 4, and at higher latitudes such as Alaska, the odd individual as old as age 5 may be found.
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