"Nature Guide Journal"
29 November
2001
A frequent news topic, salmon management recently warranted an
Associated Press release—this time about a "high-tech experiment
in management through genetics." That Oregon Department of Fish and
Wildlife (ODFW) research project is designed to gather information about
populations of hatchery and wild Umpqua River coho salmon in order to
improve fish management.
Understanding how different populations of salmon fit with others in
the natural system is a critical tool for managing those populations.
The diversity of salmon populations may be related to the diversity
of habitats used by a salmon over it's lifetime. The life cycle of
Pacific salmon populations is geographically complex. Eggs hatch in
freshwater waterways; young fish usually move to various parts of the
freshwater system, then move on to the estuarine water system; adult
fish live in salt water; adults then find their way back to the
gravel-bottomed freshwater stretch of their birth to lay the eggs of the
next generation.
By current species definition, seven different species of Oncorhynchus
are found, or have been found, in Oregon.
Our best-known species of salmon are chinook (Oncorhynchus
tshawytscha) and coho (O. kisutch)—chinook are the ones
with black spots on the top and bottom of the tail and a black mouth;
coho have black spots on only the top of the tail and a white mouth.
Generally, chinook tend to spawn and spend their early youth in the
main stem of large river systems. There are three broad spawning
populations, or "runs," of chinook, named for the season the
adults return to breed: spring, summer, and fall. Different runs of
chinook spend varying amounts of time in the estuary before going to
sea, ranging from about two months to two years. Adult chinook typically
spend two to four years at sea. Coho return from the sea in fall to
spawn primarily in tributaries. Young coho spend several months to two
years in the estuary; adults usually spend two years at sea.
Although pink salmon (O. gorbuscha) are the most numerous
salmon in the Pacific Northwest, no breeding populations are known to
remain in Oregon.
The other species of Pacific salmon found on the Oregon Coast are,
chum (O. keta), sockeye (O. nerka), steelhead (O.
mykiss), and sea-run cutthroat (O. clarkii). Steelhead have
both summer and winter runs, similar to chinook. Further, there is a
land-locked form of sockeye ("kokanee") and a resident, or
non-sea-going form of steelhead ("rainbow trout").
In general, these discrete populations of several species of salmon,
with various runs and stocks, lay eggs/hatch and grow in different
habitats in the watershed at different seasons:
they use different habitats in the watershed—or use them at different
times, for different lengths of time. At sea, the groups tend to
congregate in different regions of the sea and return after somewhat
different lengths of time.
The overall pattern is a multi-dimensional system with some kind of
salmon at some age in just about every water habitat in most seasons,
with little overlap.
This diversity of runs and stocks within each species—ODFW
identifies 55 distinct wild populations of chinook on the Oregon Coast
alone—makes for a very complex group of fish.
And a very complex management issue.
