Ageing and backcalculated length at age are based on counts and measurements of annual rings on scales or otoliths (a calcareous "earstone" found in the internal ear of fishes). The typically anadromous life history of steelhead and their ability to undergo multiple spawning migrations complicate the matter of reporting the age of fish of this species. Numerous authors have developed notation styles for this purpose. Original citations should be consulted for in-depth descriptions (e.g., Shapovalov and Taft 1954). Freshwater age is generally separated from saltwater age by either a slash (/) or period (.); for example, a fish which smolted after 2 years in fresh water and was caught after 3 years in the ocean could be represented by 2/3 or 2.3.
An allele is an alternate form of a gene (the basic unit of heredity passed from parent to offspring). By convention, the "100 allele" is the most common allele in a population and is the reference for the electrophoretic mobility of other alleles of the same gene. Other genetic terms used in this document include allozymes (alternate forms of an enzyme produced by different alleles and often detected by protein electrophoresis); gene locus (pl. loci; the site on a chromosome where a gene is found); genetic distance (D) (a quantitative measure of genetic differences between a pair of samples); and introgression (introduction of genes from one population or species into another). See also DNA and electrophoresis.
A geographic feature on the Oregon coast at 43°50 N.
A geographic feature on the California coast at 40°25 N.
Anadromous Oncorhynchus mykiss that occur in rivers from Alaska to California, including tributaries to the Fraser and Columbia Rivers largely west of the Cascade Crest. Coastal steelhead are genetically distinct from inland steelhead that occur in the Fraser and Columbia River Basins largely east of the Cascade Crest. Behnke (1992) has proposed subspecies status for these two forms and applies the taxonomic name O. m. irideus to coastal steelhead. The resident form is commonly called rainbow trout.
DNA (deoxyribonucleic acid)
DNA is a complex molecule that carries an organism's heritable information. The two types of DNA commonly used to examine genetic variation are mitochondrial DNA (mtDNA), a circular molecule that is maternally inherited, and nuclear DNA, which is organized into a set of chromosomes. See also allele and electrophoresis.
Electrophoresis refers to the movement of charged particles in an electric field. It has proven to be a very useful analytical tool for biochemical characters because molecules can be separated on the basis of differences in size or net charge. Protein electrophoresis, which measures differences in the amino acid composition of proteins from different individuals, has been used for over three decades to study natural populations, including all species of anadromous Pacific salmonids. Because the amino acid sequence of proteins is coded for by DNA, data provided by protein electrophoresis provide insight into levels of genetic variability within populations and the extent of genetic differentiation between them. Utter et al. (1987) provide a review of the technique using examples from Pacific salmon, and the laboratory manual of Aebersold et al. (1987) provides detailed descriptions of analytical procedures. Genetic techniques that focus directly on variation in DNA also routinely use electrophoresis to separate fragments formed by cutting DNA with special enzymes (restriction endonucleases).
Other genetic terms used in this document include allele (an alternate form of a gene); allozymes (alternate forms of an enzyme produced by different alleles and often detected by protein electrophoresis); chromosome (a thread-like structure containing many genes); dendrogram (a branching diagram, sometimes resembling a tree, that provides one way of visualizing similarities between different groups or samples); gene (the basic unit of heredity passed from parent to offspring); gene locus (pl. loci; the site on a chromosome where a gene is found); genetic distance (a quantitative measure of genetic differences between a pair of samples); introgression (introduction of genes from one population or species into another); and karyotype (the number, size, and morphology of the chromosome complement).
The U.S. Endangered Species Act.
Evolutionarily significant unit; a "distinct" population of Pacific salmon, and hence a species, under the Endangered Species Act.
The number of fish that survive to reach the spawning grounds or hatcheries. The escapement plus the number of fish removed by harvest form the total run size.
A life history trait of steelhead exhibited in the Rogue, Klamath, Mad, and Eel Rivers of southern Oregon and northern California. Following smoltification, half-pounders spend only 2-4 months in the ocean, then return to fresh water. They overwinter in fresh water and emigrate to salt water again the following spring. This is often termed a false spawning migration, as few half-pounders are sexually mature.
Salmon hatcheries use artificial procedures to spawn adults and raise the resulting progeny in fresh water for release into the natural environment, either directly from the hatchery or by transfer into another area. In some cases, fertilized eggs are outplanted (usually in "hatch-boxes"), but it is more common to release fry (young juveniles) or smolts (juveniles that are physiologically prepared to undergo the migration into salt water).
The broodstock of some hatcheries is based on the adults that return to the hatchery each year; others rely on fish or eggs from other hatcheries, or capture adults in the wild each year.
Anadromous Oncorhynchus mykiss that occur in the Fraser and Columbia River Basins largely east of the Cascade Crest. Inland steelhead are genetically distinct from coastal steelhead that occur in rivers from Alaska to California, including tributaries to the Fraser and Columbia Rivers largely west of the Cascade Crest. Behnke (1992) has proposed subspecies status for these two forms and applies the taxonomic name O. m. gairdneri to inland steelhead. The resident form is commonly called redband trout.
Relating to, descended from, or derived from one stock or source. See polyphyletic.
A nonmetric ordination technique used to visualize genetic relationships among populations in two or three dimensions.
Steelhead that enter fresh water with well-developed gonads and spawn shortly thereafter; commonly referred to as winter steelhead. See stream-maturing.
The phenotype is the appearance, or other observable characteristic, of an organism resulting from the interaction of the genotype and the environment.
Having more than one form (e.g., polymorphic gene loci have more than one allele).
Relating to or characterized by development from more than one ancestral type. See monophyletic.
A card (alternatively called a tag or stamp) used by steelhead and salmon anglers to record catch information; it is returned to the management agency after the fishing season.
Most salmonids deposit their eggs in nests called redds, which are dug in the streambed substrate by the female. Most redds occur in predictable areas and are easily identified by an experienced observer by their shape, size, and color (lighter than surrounding areas because silt has been cleaned away).
Spawning surveys utilize counts of redds and fish carcasses to estimate spawner escapement and identify habitat being used by spawning fish. Annual surveys can be used to compare the relative magnitude of spawning activity between years.
river kilometer (RKm)
Distance, in kilometers, from the mouth of the indicated river. Usually used to identify the location of a physical feature, such as a confluence, dam, or waterfall.
verb- The physiological process that prepares a juvenile anadromous fish to survive the transition from fresh water to salt water.
noun- A juvenile anadromous fish which has smolted.
The anadromous form of the species Oncorhynchus mykiss. Anadromous fish spend their early life history in fresh water, then migrate to salt water, where they may spend up to several years before returning to fresh water to spawn. Rainbow trout is the nonanadromous form of Oncorhynchus mykiss.
Steelhead that enter fresh water in a sexually immature condition and require several months in fresh water to mature and spawn, commonly referred to as summer steelhead. See ocean-maturing.