INTRODUCTION
The persistence of hatchery programs and of productive natural populations of anadromous fish may depend, in part, on the ability of fish managers to conserve genetic resources. Native stocks have adapted to diverse natural habitats, which improves survival over a wide range of conditions. The capacity of steelhead to persist when faced with environmental change is, in part, a function of their evolutionary history. The combined evolutionary histories of many wild stocks of steelhead determine the genetic capacity of the species to cope with environmental change. Genetic resources can be lost inadvertently by fish managers through harvest regulations, hatchery programs and practices, and other traditional management activities that tend to focus on the short term. Because fish stocks removed from their natural habitat change genetically when reared in hatcheries, the only way to conserve genetic resources of steelhead, given present technology, is by maintaining wild stocks. The Oregon Department of Fish and Wildlife’s Wild Fish Management Policy (1992) was adopted out of recognition of the importance of genetic resources to the long-term health of fish species in Oregon.
People influence the genetic diversity of wild fish by altering habitats, by harvesting fish, and by stocking hatchery fish. The goal of our steelhead study was to provide information that would help decrease the risk of detrimental effects of hatchery programs on the genetic characteristics of wild steelhead. We assumed that hatchery fish would continue to be an important part of Oregon’s steelhead management program.
We provided information in several subject areas so managers could develop strategies to reduce genetic risk to wild steelhead populations. First, we helped identify geographic boundaries of wild steelhead populations so managers could identify streams where hatchery stocks were incompatible with wild native stocks. Secondly, we defined the magnitude of hatchery straying and the origin of these strays in coastal populations because strays constituted genetically dissimilar fish and, consequently, were restricted under the Wild Fish Management Policy.
Third, we determined the percentage of hatchery fish that spawned with wild fish in selected coastal rivers and looked at methods managers could use to monitor this percentage. These data could be used to determine the status of hatchery programs relative to guidelines in the Wild Fish Management Policy. Fourth, where transplanted stocks had been used in the past, we compared the performance of hatchery adults that originated from local wild brood stock with that of hatchery adults originating from transplanted hatchery brook stock. Although the use of local brood stocks in hatcheries would reduce the risk of genetic impacts on wild fish, managers needed to know how the change to local brood stocks might impact sport fisheries. Finally, we investigated two strategies for reducing interbreeding of hatchery with wild steelhead on the spawning grounds. We evaluated the use of an acclimation period prior to release to direct returning adults to a collection site where they could be removed from the spawning population. We also evaluated sterilization as a method for producing hatchery fish that would not spawn with wild fish but would contribute to recreational fisheries.
Designation of wild fish populations:
Wild populations of steelhead have adapted to physical and biological conditions present within the basins in which they spawn and rear. Conservation of genetic resources requires that variation within populations and variation among populations be maintained. Although within population variation appears to be far greater than among population variation in rainbow trout in the Columbia River drainage. Parkinson found significant biochemical differentiation between steelhead populations in adjacent streams in British Columbia. Patterns of allelic variation in the steelhead stocks geographically close tend to be more similar than stocks geographically distant. Some exchange between populations surely exists and is an important attribute of the species. Meffe points out that Variance among naturally isolated populations, however subtle, should be preserved and exploited through continued isolation wherever possible.ä Parkinson and Schreck suggest that as many separate stocks be maintained as possible.
The transfer of steelhead stocks among basins is one hatchery practice that could reduce survival of wild fish because of interbreeding between locally adapted native populations and less-adapted, transplanted stocks. The primary purpose for delineating stock boundaries was to formally identify these native populations so that steelhead management programs, especially hatchery programs, could be designed to minimize genetic risks to wild populations.
In general, each of the major basins in Oregon and in some cases subbasins within major basins were designated as separate steelhead stocks. Later reports refined this listing (see Kostow 1995) and identified management strategies for some steelhead populations (ODFW 1994).
Stray hatchery steelhead in Oregon coastal rivers:
Homing to a natal site is characteristic of salmonids, but mature fish that migrate to and spawn in a stream other than their natal one are considered strays. Straying is a natural component of salmonid behavior that enables fish to colonize new habitat and to avoid locally unfavorable conditions. However, straying of hatchery fish concerns fish managers because of potential negative impacts on wild populations of interbreeding with hatchery fish.
Our study·examined the degree and origin of straying of hatchery winter steelhead among several major river basins on the Oregon coast.
In Oregon coastal rivers where hatchery steelhead were released, the incidence of stray hatchery fish ranged from 4 to 26% of the total sample. The highest incidence of straying was in the Alsea River, where over 25% of the total catch was composed of stray hatchery fish.
Stray hatchery steelhead composed an average 22% of the composition of winter steelhead in five streams where no hatchery fish were released. The percentage of stray hatchery fish exceeded 10% in the five streams (Oregon’s Wild Fish Policy sets a standard of 10% for strays when the stray fish are not native to the river where they are found). Most of the stray hatchery fish in these two streams were from large out-system hatchery releases made in nearby rivers.
Stray hatchery steelhead increased the occurrence of hatchery steelhead in rivers where hatchery fish were released by an average of 5%. The additive percentage of straying and homing hatchery steelhead in 11 coastal rivers where hatchery fish were released composed a mean of 58% (range 26 to 87%) of the total sample. Lirette and Hooton reported in 1988 that stray hatchery steelhead accounted for an average 14% (range 0 to 44%) of the total hatchery catch in 9 Vancouver Island basins.
Generally most stray hatchery steelhead in the surveyed streams were from nearby releases. Of the known strays in 16 streams, releases from adjacent streams (defined as the nearest basin receiving hatchery fish north and south of the mouth of the subject stream) accounted for 57% of the strays and composed the majority of strays in 10 of the 16 sampled streams.
Use of a local brood stock appeared to reduce the incidence of strays in the home or rearing basin, and in other basins. Interestingly, the return to the Alsea basin of Alsea steelhead reared and released in the Umpqua suggests some imprinting at the egg development stage or a genetic component for homing.
Steelhead transplanted from Alsea Hatchery were particularly apt to stray accounting for 84% of the known stray hatchery fish in the Alsea River, and composed the highest percentage of strays in other rivers compared to other releases.
Stray hatchery fish create difficulties in attempts to manage rivers for naturally producing populations. Under Oregon’s Wild Fish Management Policy, only 10’% of the naturally spawning population may be composed of genetically dissimilar fish. Stray hatchery steelhead composed 10% or more of the total catch in 10 of 16 Oregon coastal rivers.
The genetic integrity of locally adapted populations can decrease with rates of migration (and gene flow) from stray hatchery fish as low as 5-10%, especially when selection pressures maintaining local adaptations are lower than the rate of gene flow between populations. NMFS has used an interim straying guideline of less than 5% of the naturally spawning population to limit the proportion of stray, non-native hatchery fish.
·our winter steelhead research indicated that the composition of hatchery and wild steelhead in fisheries was similar to that measured on spawning grounds.
We believe the proportions of stray hatchery steelhead we measured in the total catch of rivers is a good measure of the interbreeding potential between the non-native hatchery fish and the naturally produced fish in those rivers. Stray hatchery fish can potentially affect wild populations through reduction in fitness of the wild populations by spreading deleterious alleles, through elimination of genetic differences between hatchery and wild populations, and through demographic effects such as harvest in mixed fisheries and competition.
In our study, the two predominate factors that contributed to straying in Oregon coastal basins were releases in nearby basins and releases of transplanted stocks. Another factor contributing to straying was steelhead returning to their rearing basin instead of their release basin.
Possible solutions to reducing the number of stray hatchery fish in problem streams include use of local brood stock, direct stream releases in tributaries to increase homing, rearing and release within natal basins, reduction in hatchery releases, or a combination of these strategies. ·homing of winter steelhead to release sites in tributary streams was highly accurate
Overlap of hatchery and wild spawners:
Because fishery data were used, in part, to measure the degree of hatchery straying and the origin of strays, we wanted to know if fishery data reflected the actual proportion of hatchery fish in natural spawning populations. We also wanted to know if hatchery and wild fish overlapped in time and space during spawning. (Based on the Wild Fish Policy) up to 50% of the natural spawning population can be hatchery-reared if native brood stock is used and wild fish are incorporated annually into the brood stock. The use of transplanted (or stray) hatchery fish lowers the percentage to 10% or less.
The conclusion of this part of the study showed: The hatchery and wild composition of the catch of winter steelhead in sport fisheries reflects the composition on spawning areas and is adequate to determine compliance with Wild Fish Management Policy, especially when management (the number of hatchery fish) is far from the criteria specified in the policy. In all basins, there was considerable overlap in spawn timing between hatchery and wild steelhead although wild fish tended to spawn later and over a longer time period than hatchery fish.
Use of local brood stock in hatchery programs:
The use of locally adapted native stocks in hatchery programs recognizes that these stocks are best suited for survival in natural environments and that their use in hatcheries will reduce genetic risks from interbreeding with wild stocks. Native populations of wild steelhead have evolved life history strategies, body form, and physiology that increases survival in their environment.
With this portion of the study, we provide managers with a comparison of performance between hatchery releases of a local stock with that of a transplanted stock. The performance compared were relative return rate and contribution to fisheries. An unexpected difference in straying was also observed.
Relative survival from smolt-to-adult was not significantly different between the Siuslaw (native stock) and Alsea (transplanted non-native stock) smolts released into the Siuslaw River in 1991, 1993 and 1994. In addition, overall contribution to the recreational fishery in the Siuslaw River was not significantly different between the two stocks. Although not statistically different, estimated catch of Siuslaw stock in the Siuslaw River sport fishery was higher than that of Alsea stock in 2 of the 3 years sampled.
Siuslaw stock adults tended to migrate later than Alsea adults. The later migration timing shifted recreational harvest of Siuslaw fish into March compared with the Alsea stock.
The later migration timing of Siuslaw stock was related to the time eggs were collected from their parents. In all three years over 60% of the eggs from Siuslaw brood stock were taken after March 1, but only an average of 8% of the eggs of Alsea brood stock were taken after that date. The egg take for the 1991 release was the latest of all three years with all of the eggs taken after March 1 and 83% taken after April 1. Several authors have found that migration timing is a heritable trait in anadromous salmonids.
Alsea River steelhead reared at Alsea Hatchery and released as smolts into the Siuslaw River have strayed at a high rate as adults back to the Alsea River rather than returning to the Siuslaw River. The Siuslaw stock reared at Alsea Hatchery but released into the Siuslaw River returned as adults at a higher rate and straying was reduced by 50% using locally adapted Siuslaw River brood stock. Increased homing to the Siuslaw contributed to higher catch of Siuslaw stock than Alsea stock in two of the years sampled.
Lower stray rates of the locally adapted Siuslaw stock and higher stray rates of Alsea stock into the Alsea River suggest a hereditary component in homing behavior of steelhead. This suggest heredity was a component of homing behavior although we cannot rule out differences in imprinting that may have occurred prior to the eyed-egg stage. Evidence from other studies suggest a genetic component in homing of chinook and pink salmon.
Reducing interbreeding of hatchery with wild fish:
We evaluated two potential management strategies that could reduce interbreeding of hatchery with wild fish. Acclimating hatchery juveniles at release sites prior to release to improve homing has been suggested as a strategy for segregating returning adults from wild fish. Sterilizing hatchery fish to prevent spawning with wild fish was another strategy discussed early in the development of the Wild Fish Management Policy.
Acclimation of juvenile steelhead:
Homing within the Siuslaw River was high for acclimated and direct stream releases, demonstrating that a tributary release strategy can be used to contain hatchery spawning escapement.
We found that acclimation of winter steelhead smolts did not increase survival over that of a direct tributary release into the Siuslaw Basin. Data on steelhead releases in British Columbia also indicated that acclimating steelhead smolts did not increase survival relative to direct release groups.
Acclimating juvenile Alsea stock steelhead in the Siuslaw basin prior to release did not reduce straying of adults to the Alsea River.
We found that Siuslaw stock steelhead, reared at Alsea Hatchery, strayed less to the Alsea basin than Alsea stock reared at the hatchery. Both stocks were released as smolts into the Siuslaw River. Straying was reduced by more than 50% over 3 years by using local Siuslaw brood stock.
The findings from our experiment do not support the use of acclimation facilities to improve homing or survival of winter steelhead. Our results show that tributary releases, when used in conjunction with a trap to collect returning adults, can be used to reduce the number of hatchery fish that spawn with wild fish while still providing fisheries.
We found no difference in the number of juvenile residuals between acclimated and direct stream release groups. Residualism of hatchery smolts seems to be related more to the size of the fish than to whether they are acclimated.
The purpose of attracting adult hatchery steelhead to a particular tributary ultimately is to reduce the number of hatchery fish spawning with wild fish by removing the hatchery fish.
Recycling adult steelhead:
During the last three years of our acclimation evaluation we examined the feasibility of recycling adults downstream into fishery areas of the Siuslaw River. We recycled hatchery adult steelhead through the fishery to determine if we could provide additional sport fishery benefits from these surplus fish without increasing straying to wild spawning areas.
Anglers caught an average of 10.7% of the steelhead recycled into downstream areas. Not all steelhead recycled are caught or return to the tributary where they were originally captured. In the 3 years fish were recycled, an average of only 44% could be accounted for in traps and in the sport fishery. Although homing accuracy for first time recycles was high, homing fidelity decreased with subsequent recycling trips. Mortality from handling fish does not explain the high number of missing fish.
Sterilization:
The use of an androgen to sterilize hatchery steelhead was examined as a way of preventing interactions between wild and hatchery fish on spawning grounds. The objective of our work was to determine if sterilized hatchery steelhead would return at a rate high enough to provide recreational harvest while giving managers an option for reducing interactions with wild fish.
The mean smolt-to-adult return rate for 3 years of releases combined was 2.2% for control groups and 0.5% for treatment (sterilized) groups, a four fold reduction in survival. The treatment significantly reduce return frequencies by 75%, 71%, and 80% for the 1990, 1991, and 1992 releases respectively. The treatment also delayed maturation. Treatment groups returned at an older age than the control groups. Adults that spent three summers in the ocean composed 61%, 63%, and 30% of the treatment returns by release year compared to 27%, 36%, and 10% of the control group returns·
Treatment groups averaged 80% male and 20% female. The mean for control groups was 49% male and 51 % female. Only one treatment fish appeared truly sterile·.
Most of the returning fish were males that develop secondary sexual characteristics and were not sterile. The presence of gonads indicates the males would likely be sexually active. Incompletely sterilized males may compete with fertile males on spawning grounds, but most sterilized fish would not spawn successfully due to physiological changes. Consequently, treating hatchery steelhead · is not an alternative for reducing hatchery fish interactions with wild stocks.