Except where specifically noted, the life-history information presented below applies to coastal steelhead and does not include inland steelhead of the Columbia and Fraser River Basins.

Anadromy-Nonanadromy

The question of the relationship between anadromous and nonanadromous forms of salmonid species has been widely examined, perhaps most intensively for sockeye and kokanee salmon (O. nerka). Foote and Larkin (1988) examined assortative mating between sockeye and kokanee salmon and found that male mate choice was dominated by form; that is, kokanee males demonstrated preference to spawn with kokanee females rather than sockeye females. Neave (1944) determined that anadromous and nonanadromous O. mykiss of the Cowichan River, Vancouver Island, constituted distinct "races" based on scale counts and migration behavior.

Allendorf (1975) found that the genetic distinction between coastal and inland O. mykiss applies to both life-history forms; that is, rainbow trout east of the Cascades are genetically more similar to steelhead from east of the Cascades than they are to rainbow trout west of the Cascades. Most recent studies of O. mykiss have focussed on either rainbow trout or steelhead and thus provide no direct information about the relationship between the forms on a finer geographic scale. However, some protein electrophoretic studies that have reported data only for "rainbow trout" probably included samples of steelhead as well (Currens - footnote 2 ). For example, in the John Day River, an Oregon tributary of the Columbia River, genetic differences between O. mykiss from the North and South Forks were larger than differences between presumed steelhead and rainbow trout in the South Fork (Currens et al. 1987). In the Deschutes River, another Oregon tributary of the Columbia River, Currens et al. (1990) found much larger genetic differences between O. mykiss from above and below a barrier falls than between presumed steelhead and rainbow trout from below the falls.

In a study of mitochondrial DNA (mtDNA) in O. mykiss, Wilson et al. (1985) found that coastal populations of steelhead and rainbow trout were distinct from each other, even when sampled from the same river basin. However, steelhead and rainbow trout from interior British Columbia clustered in the same clonal line as rainbow trout from Alberta. Interpretation of these results is difficult because of the small sample sizes and dispersed sampling that included rainbow trout from California and Alberta whereas all steelhead samples were from British Columbia. Furthermore, Buroker (footnote 3) found that a mtDNA marker Wilson et al. (1985) reported as characteristic of rainbow trout was the most common marker in Buroker's study of North American steelhead.

Steelhead Run-Types

Across their distribution, steelhead return to fresh water throughout the year, with seasonal peaks in migration activity. These seasonal peaks are used to name and describe various runs. In Alaska, the runs are called fall and spring; in British Columbia, Washington, Oregon, and California, the runs are usually called summer and winter. Large rivers, such as the Klamath and Rogue Rivers, may have adult steelhead migrating throughout the year (Shapovalov and Taft 1954, Rivers 1957, Barnhart 1986), with several vernacular run names. For example, what is now known as summer steelhead in the Rogue River was historically divided into spring and fall steelhead (Rivers 1963). Run-type designation for steelhead in the Klamath and Trinity Rivers continues to be perplexing, particularly with respect to what is historically called fall-run steelhead. Everest (1973) and Roelofs (1983) contend that spring and fall steelhead of the Rogue, Klamath, Mad, and Eel Rivers are in fact summer steelhead based on lack of segregation at spawning, and the observation that sport fisheries for fall steelhead are limited to rivers with summer steelhead. However, other biologists classify fall steelhead separately (e.g., Heubach 1992) or as winter steelhead. Roelofs (1983) identified the need for research to identify the relationship between fall-run and summer-run steelhead of the Klamath and Eel Rivers. In this document, spring- and fall-run steelhead of the Klamath Basin are considered summer steelhead.

Biologically, steelhead can be divided into two basic run-types, based on the state of sexual maturity at the time of river entry and duration of spawning migration (Burgner et al. 1992). The stream-maturing type (fall-run in Alaska, summer-run elsewhere) enters fresh water in a sexually immature condition and requires several months in fresh water to mature and spawn. The ocean-maturing type (spring-run in Alaska, winter-run elsewhere) enters fresh water with well-developed gonads and spawns shortly thereafter. This document uses the terms summer-run or summer steelhead to refer to the stream-maturing type and winter-run or winter steelhead to refer to the ocean-maturing type.

In the Pacific Northwest, steelhead that enter fresh water between May and October are considered summer-run, and steelhead that enter fresh water between November and April are considered winter-run. Variations in migration timing exist between populations. Some river basins have both summer and winter steelhead, while others have only one run-type.

Distribution of coastal steelhead run-types--It is difficult to accurately describe the historical distribution of coastal steelhead run-types due to the muddled history of O. mykiss taxonomy and local vernacular terms for steelhead of various run-times. Current distribution of coastal steelhead run-types is described in varying detail by several authors (Roelofs 1983, Barnhart 1986, Pauley et al. 1986, Burgner et al. 1992). Winter steelhead utilize coastal streams from Yakutat, Alaska to Malibu, California (Burgner et al. 1992). Summer steelhead are discontinuously distributed across the same range, presently extending as far south as the Middle Fork of the Eel River (Roelofs 1983). California Department of Fish and Game records indicate summer steelhead may have existed in the Sacramento Basin prior to the construction of several dams in the 1940s-1960s (McEwan and Jackson in prep.). Table 3 shows the river basins in Washington, Oregon, and California that support natural runs of coastal summer steelhead alone and co-ocurring coastal summer and winter steelhead.

Temporal and spatial separation of spawning--Although time of stream entry is generally well documented for summer and winter steelhead, there is relatively little information on time and location of spawning. Both summer and winter steelhead spawn in the winter to early spring. Difficult field conditions at that time of year and the remoteness of spawning grounds contribute to the lack of specific information on steelhead spawning (USFWS 1956, Roelofs 1983).

In drainages with both summer and winter steelhead, there may or may not be temporal separation of spawning between the two run-types. Based on tagging upstream migrating steelhead and surveying spawning areas, Everest (1973) described spawning for Rogue River summer steelhead as December-March and for winter steelhead as March-June; thus, there is some overlap. However, Everest stated that peak spawning activity for the run-types was separated by about 60 days. Neave (1949) stated that the two run-types of steelhead in the Cowichan River, Vancouver Island, British Columbia, spawn in January-March and April-May, respectively; this indicates temporal segregation of these spawning populations.

Run-timing of Illinois River steelhead--The Illinois River is generally considered to have only winter steelhead (Jennings - footnote 4). Historically, there may have been a weak run of summer steelhead in the Illinois River (Rivers 1957). Recent Forest Service records describe the occurrence of one apparent summer steelhead in the Illinois Basin in 1990 (USFS 1992, Busby et al. 1993). Whether the Illinois River at one time had its own run of summer steelhead, or whether summer steelhead observed in the river are actually migrants from the Rogue River, is not certain. Everest (1973) stated that prior to the construction of the flow-regulating Lost Creek Dam, summer steelhead from the Rogue River sought thermal refuge in the lower Illinois River; Everest (footnote 5) believes these may have been the summer steelhead that Rivers (1957) described in the Illinois River.

Age Structure

Steelhead exhibit a diverse array of life-history patterns with variations in smolt age, saltwater residence, and spawning activity. As a case in point, Oregon Department of Fish and Wildlife (ODFW) has identified 15 life-history patterns among wild summer steelhead in the Rogue River (ODFW 1994). The different life-history patterns are found at different frequencies among steelhead populations. The most common pattern for wild coastal steelhead south of Alaska is to smolt after 2 years in fresh water, then return to spawn after 2 years in salt water (Table 4 and 5), whereas steelhead reared in hatcheries usually smolt at 1 year (Chapman 1958, Lindsay et al. 1991). In Alaska, wild steelhead usually smolt at 3 years (Sanders 1985). There may be a latitudinal cline to these life-history patterns (Withler 1966), with increases in age at smolting and spawning at higher latitudes (Table 4 and 5). Titus et al. (in press) found no statistical evidence for a latitudinal cline in steelhead smolt age from California to British Columbia; however, they did find that saltwater age at spawning (and mean adult length) did increase with increasing latitude.

Steelhead may survive spawning, return to the ocean, and spawn again in subsequent years. Up to five spawning migrations have been recorded for individual steelhead (Bali 1959, Lindsay et al. 1991); however, more than two is unusual. Columbia River steelhead are essentially semelparous (Long and Griffin 1937, ODFW 1986), typically completing only one spawning migration. Repeat spawners are predominately female due to higher post-spawningmortality among males (Shapovalov and Taft 1954, Maher and Larkin 1955, Chapman 1958, Withler 1966, ODFW 1986, Burgner et al. 1992). Incidence of repeat spawning tends to decrease from south to north (Withler 1966), with much variation among populations (Table 6).

Half-Pounders

Steelhead with the life-history pattern called "half-pounder" (Snyder 1925) are steelhead that return from their first ocean season to fresh water from July through September, after only 2 to 4 months of saltwater residence. They generally overwinter in fresh water before outmigrating again in the spring. There is some variability in criteria for defining half-pounders. Kesner and Barnhart (1972) described Klamath River half-pounders as being 250-349 mm. Everest (1973) used 406 mm as the upper limit of half-pounder body length on the Rogue River.

The half-pounder migration has been termed a "false spawning run" because few half-pounders are believed to be sexually mature. However, Everest (1973) found some spawning activity by male half-pounders that were 355-406 mm in length.

Half-pounders are reported in the scientific literature from the Rogue, Klamath, Mad, and Eel River drainages of southern Oregon and northern California (Snyder 1925, Kesner and Barnhart 1972, Everest 1973, Barnhart 1986). Anecdotal accounts suggest that the half-pounder life history may also occur outside of these basins. However, the lack of either a half-pounder fishery outside the Rogue, Klamath, Mad, and Eel Rivers or scientific documentation suggests that if it occurs in other locations, the half-pounder strategy is less successful than in the basins named above and occurs at a much lower frequency.

Half-pounders are generally associated with summer-run steelhead populations. However, this trait has also been identified in winter-run steelhead, albeit at a lower frequency. For example, Hopelain (1987) found a half-pounder frequency of 23.2% among lower Klamath River winter-run steelhead, as compared to a mean frequency of 95.2% among fall-run (summer) steelhead from six Klamath River tributaries. Scale analysis of Rogue River winter steelhead initially collected for Cole Rivers Hatchery broodstock indicated a half- pounder frequency of approximately 30% (Evenson - footnote 6).

Presumably, the half-pounder life history occurs either to avoid a deleterious condition in the ocean or to exploit a beneficial condition inland. However, since half-pounders were first described in the literature (Snyder 1925), little additional information has been published, and no convincing theories to explain half-pounders have been advanced. It is not known to what degree this trait is due to genetic as opposed to environmental factors. In initiating the winter-run steelhead broodstock at Cole Rivers Hatchery (on the Rogue River), scale patterns were used to select fish that lacked the half-pounder life history (Evenson footnote 6). Recently, however, there is evidence of half-pounders among winter-run steelhead returning to the hatchery. Cramer et al. (1985, p. 112) stated that the "occurrence of the half-pounder life history has increased among winter steelhead released from Cole Rivers Hatchery since the time that growth rates of parr in the hatchery have been accelerated in order to produce age 1 smolts." These findings suggest that the incidence of the half-pounder life history can be influenced by environmental conditions.

Illinois River steelhead scale data from ODFW (1992b) indicate that of 163 steelhead angled between January 1982 and February 1990, 158 were mature adults and 5 (3%) were half-pounders. It is possible that the few half-pounders had roamed from their natal stream and were not of Illinois River origin. The ODFW data do not indicate whether any of the mature adults had scale patterns indicative of previous half-pounder runs. Anglers have reported to NMFS that half-pounders are indeed present, and caught, in the Illinois River (Beyerlin 1992, Leseman 1993).

Although half-pounders occur at a much lower frequency among Illinois River steelhead than Rogue River steelhead, the Illinois River is not unique among coastal steelhead streams in not having half-pounders. In fact, most steelhead populations coastwide do not have this life-history trait. We were unable to determine whether other river basins besides the Rogue River that have half-pounders (i.e., the Klamath, Mad, and Eel Rivers) have tributaries, like the Illinois River, in which the trait is rare or absent.

Oceanic Migration Patterns

Anadromous salmonids are known to demonstrate stock-specific differences in oceanic migrations. Examples of this are seen in data from coded-wire-tag recoveries of hatchery reared salmon (Table 7). Chinook (O. tshawytscha) and coho (O. kisutch) salmon released from ODFW hatcheries north of the Rogue River are recovered in the ocean off Alaska, British Columbia, and Washington at greater frequencies than are salmon from the Rogue and Chetco Rivers. Conversely, southern Oregon stocks of salmon are recovered in the ocean fishery off California at greater frequencies than are the northern stocks. Nicholas and Hankin (1988) found that chinook salmon from Oregon rivers south of Cape Blanco (e.g., the Rogue and Chetco Rivers) generally rear in the ocean off southern Oregon and northern California, while chinook salmon from Elk River and basins to the north generally rear in the ocean as far north as Alaska; these stocks are termed "south-migrating" and "north-migrating," respectively. An anomaly in this pattern is spring-run chinook salmon from the Umpqua River; Nicholas and Hankin refer to this as a "north-and-south-migrating" stock because they rear in the ocean from northern California to Alaska (Table 8).

Straying

Based on tag returns, Everest (1973) found evidence of straying by summer steelhead between the Rogue and Klamath River Basins. Some of this straying was by half-pounders, but adults also strayed. According to Everest (1973, p. 31), "[s]trong physical and behavioral similarities exist between summer steelhead populations in the two systems and strays from the Rogue probably reproduce successfully with Klamath stocks."