We compared the relative reproductive success of naturally spawning, summer-run hatchery and wild steelhead trout Salmo gairdneri by electrophoretic examination of juveniles for a specific genetic marker. The success of hatchery fish in producing smolt offspring was only 28% of that for wild fish. We also found that 62% of the naturally produced summer-run smolts were offspring of hatchery spawners. Their dominance occurred because hatchery spawners, within the watershed we examined, effectively outnumbered wild spawners by at least 4.5 to 1. We suggest that, under such conditions, the genetic integrity of wild populations may be threatened. We also suggest that hatchery fish may be an important component of the spawner-to-smolt recruitment relationship for summer-run steelhead. 726

No abstract

We differentially tagged upstream migrant adult summer and winter steelhead trout (Salmo gairdneri) of hatchery and wild origin in the Kalama River, Washington, and subsequently observed them spawning under natural conditions in a tributary. We found that summer steelhead spawned within the study stream on a spatially random basis. The steelhead spawning interval was 6 mo long, during which hatchery summer steelhead spawned first, followed by wild summer, hatchery winter, and wild winter steelhead. Significant temporal spawning differences were found between hatchery summer and wild winter fish, and between wild summer and wild winter steelhead. We developed estimates of potential reproductive overlap between spawner groups that indicated that most reproductive activity involved members of the same spawner group. Estimated genetic exchange among groups was primarily between hatchery and wild fish within races. Of all possible spawner group comparisons, the smallest potential reproductive overlap estimated was between wild summer and wild winter steelhead. We concluded that, although wild summer and wild winter steelhead were not completely reproductively isolated, a substantial degree of successful gene flow restriction occurred, thereby providing a mechanism for the maintenance of racial identity. Additionally, spatial and temporal spawner segregation was of insufficient magnitude to prevent the potential infusion of hatchery steelhead genes into the wild summer steelhead population.

The potential for hatchery fish to negatively impact wild fish has been identified as a concern for dwindling stocks of naturally produced anadromous salmonids in the Pacific Northwest. Using a control–treatment approach, we performed a multiscale examination of potential behavioral impacts of releases of hatchery‐produced steelhead Oncorhynchus mykiss (anadromous rainbow trout) on preexisting wild populations of O. mykiss (anadromous and potamodromous) over a 4‐year period. We released approximately 33,000 conventionally reared hatchery steelhead smolts (treatment) into an upper Yakima River tributary in 1991, 1992, 1993, and 1994 and investigated behavioral interactions and small‐scale displacement (0.2–5.0 m). Snorkelers conducted behavioral observations and observed small‐scale displacements in treatment and control streams for approximately 1 month following releases. Hatchery steelhead were generally larger than wild O. mykiss and dominated most (68%) contests. The types of behavioral interactions observed differed between control and treatment streams (P < 0.01). Behavioral interactions involving physical contact (e.g., nips) were observed more frequently in treatment streams than in control streams, whereas those involving nonphysical contact displays (e.g., threats and chases) were more frequent in control streams. Contrary to our expectations, total behavioral interaction rates were generally higher in control streams than in treatment streams, though the difference was not statistically significant (P = 0.07). Hatchery steelhead displaced wild O. mykiss in 79% of the contests observed between these groups. Our results indicate that the behavior of hatchery steelhead can pose risks to preexisting wild O. mykiss where the two interact. Strategies to minimize undesirable risks associated with behavior of released hatchery steelhead should be addressed if protection and restoration of wild O. mykiss stocks is the management goal.

Leider, S. A., M. W. Chilcote, and 1. I. Loch. 1986. Comparative life history characteristics of hatchery and wild steelhead trout (Salrno gairdneri) of summer and winter races in the Kdlama River, Washington. Can.I. Fish. Aquat. Sci. 43: 1398-1409. Life his tor^ information was collected frorn adult upstream migrant haichery and wild steelhead trout (Salrno gairdneri) of summer-run and winter-run racial origin in the Kalama River, Washington, from 1976 to 1984. We found inter-and intraracial distinctions among many of the characteristics examined. In contrast with winter steelhead, summer steelhead generally had a tempori~lly protracted time of return, fewer total age categories, fewer repeat spawners, and greater size at a given marine age. Compared with wild steelhead, hatchery steelhead generally had fewer saltwater age categories and a sower incidence of respawners. Based on differences in return timing, age composition, and sine at maturity, we suggest that greater similarities currently exist between Kalarna River hatchery and wild summer steelheid than between hatchery and wild winter steelhead. Des renseignemens sur le cycle vital de truites arc-en-ciel (Salrno gardnerii adultes sauvdges et d'elevage de races (( remont6e ej'etk )) et ! < remontee d'hiver )), en migration d'amont dans la rivi6t-e Kalarna (Washington), ont 6t6 rec~reillis de 4 976 . $I 1984. Bon nombre des caract6ristiqties etudikes prher-staient des &carts inter-raciaux et intra-raciaux. iau contraire efes truites d'hiver, les truites d'et6 laresentaient generalernent un moment de retour temporairement retar&, un nombre total inf6rieur de catkgories d'2ge, moins de gkniteurs ayant d6jA fra 6 et une taille plus grande pour un age marin donn4. Comparativernent aux truites sauvages, les truites $&levage presentaient gkn6ralement moins de cat6gories &Age en eau salee st un moins grand pourcentage de gbniteurs ayant dkj3 fray&. En se basant sur les diffirences ayant trait au moment du retour, a la composition des iges et 2 la taille a maturite, les auteurs proposent Ifhypothese qu'll existe actuellement plcts de similitudes entre les truites d'elevage et sauvages d'etc? yu'entre les truites d'6levagc e.t sauvages d'hiver de [, a riviPre Kalama.