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Salmonid Life History
Salmon and some trout have a unique life cycle - called "anadromous" - that takes them from the freshwater streams of their birth to the ocean during maturity and back to the streams to start a new generation. These fish are known as "salmonids."
Each year, adult salmonids of various ages return to the streams of their birth using a combination of olfactory and other senses to locate their natal stream (Allen and Hassler 1986). In locations with appropriate environmental conditions, females create a redd - a gravel nest - and deposit their eggs where they will be fertilized by one or more males (Sandercock 1991). Environmental conditions are very important for the developing embryos. Pollutants and sediment can harm them and extreme flow could sweep them away. The young - known as alevin - emerge from the egg with a yolk sac attached.They remain in the gravel for between two and seven weeks and during that time, are very sensitive to changes in temperature and oxygen levels (Sandercock 1991).
Salmonid alevin. Photo courtesy of “Salmon Life Cycle” Web page, an educational site for elementary school students.
When they emerge from the gravel, the juveniles - known as fry - grow rapidly. Coho and most steelhead fry stay in fresh water for at least a year. Chinook may venture into saltwater within 60 - 150 days post-hatch, or they may stay in freshwater for one to three years (National Oceanic and Atmospheric Administration National Marine Fisheries Service 1998). While they remain in their natal stream, factors important to salmonid survival and growth are food and space (Thomas R. Payne & Associates 1989). Prior to entering the ocean, salmonids undergo smolting, the physiological adjustment from fresh to salt water.
Little is known about the ocean phase of the salmonid life cycle, except that the fish spend several months to several years eating, growing, and avoiding predators. Coho typically spend about two years in the ocean while steelhead spend anywhere from several months to three years in the ocean. Chinook typically spend three to four years at sea with about 25% of each year?s spawning run made up of two-year-old males (Allen and Hassler 1986). The adult salmonids migrate to their natal streams to begin the cycle anew. Chinook and coho salmon are semelparous, meaning that they die after spawning, but steelhead are iteroparous, meaning that they may return to spawn a few times during their life.
Spawning coho.
References
Allen, M.A., and T.J. Hassler. 1986. "Species Profiles: Life History and Environmental Requirements of Coastal Fishes and Invertebrates (Pacific Southwest) -- Chinook Salmon." U.S. Army Corps of Engineers, TR EL-82-4. USFWS Biological Report 82(11.49), 26 pp.
Myers, James M., R. G. Kope, G. J. Bryant, D. Teel, L. J. Lierheimer, Thomas. C. Wainwright, W. Stewart Grant, F. William Waknitz, Kathleen Neely, Steven T. Lindley, and Robin S. Waples. 1998. Status Review of Chinook Salmon from Washington, Idaho, Oregon, and California. National Oceanic and Atmospheric Administration National Marine Fisheries Service, Status Review of West Coast Chinook. Available at: http://www.nwfsc.noaa.gov/publications/techmemos/tm35/index.htm#toc
Sandercock, F.K. 1991. The History of Coho Salmon (Oncorhynchus kisutch). In Pacific Salmon Life History, edited by C. Groot and L. Margolis. Vancouver: University of British Columbia Press.
Thomas R. Payne & Associates (1989). Freshwater and Estuarine Requirements of Salmonids with a Summary of Logging Impacts and Mitigation and a Critique of the Morford Report for the Big River Watershed. San Mateo, Ralph Osterling Consultants, Inc. : 20.
