Ocean Life

Having entered the ocean as young adults and spent months to years eating, growing, and avoiding predators, salmonids return to freshwater to spawn and start the next generation. During their ocean travels, salmon may cover thousands of kilometers before navigating back to the stream of their birth. Coho salmon (Oncorhynchus kisutch) typically spend two years at sea, while steelhead trout (O. mykiss) are more variable, spending from a few months to three years. Little is known about the ocean phase of the salmonid life cycle – simply that it is different for different species and varies regionally (City of Seattle 2004).

Salmonid navigation at sea is not fully understood. A number of mechanisms are thought to be used for guidance at sea including use of receptors that detect changes in the earth’s magnetic field and guidance by the stars. Ocean currents may also play an important role in navigation. When salmon are closer to shore, they are guided by chemical memory, homing to substances (including pheromones) present in streams in minute quantities (Atlantic Salmon Trust 2004).

Sexual Maturity

During their ocean-phase salmon have camouflaging coloration, with silver-colored sides, whitish bellies and dark-bluish backs. Males and females are similar in appearance with no distinguishing sexual characteristics. As salmon develop towards sexual maturity this protective coloration is lost and differences between the sexes develop.

Coho - Ocean Stage	Coho - Sexually Mature

Steelhead

Images courtesy of the National Oceanic and Atmospheric Administration.

References

Atlantic Salmon Trust. 2004. Atlantic Salmon Facts – Salmon Biology [Web page] [cited 2004]. View on-line source .

City of Seattle. 2004. Salmon Friendly Seattle: Habitat Salmon Needs at Each Stage of the Life Cycle [Web page] [cited 2004]. View on-line source .

General References

Barnhart, R.A. 1986. "Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Pacific Southwest) -- Steelhead." U.S. Army Corps of Engineers, TR EL-B2-4. USFWS Biological Report 82(11.60), 21 pp. View on-line document.

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.