HATCHERY SUMMER STEELHEAD IMPACT ON WILD WINTER STEELHEAD

Kostow, K.E. and Steven R. Phelps. 2001. Oregon Department of Fish and Wildlife. Portland, Ore. In Press.

ABSTRACT: Hatchery summer steelhead were introduced into the Clackamas River, Oregon, USA in 1973. This study demonstrates impacts to the productivity of the native wild winter steelhead population caused by the passage of large numbers of hatchery adults into natural spawning habitats. The impacts are ecological since interbreeding between the hatchery and wild fish is precluded by differences in life history. Genetic admixture analysis was used on naturally-produced out-migrating steelhead smolts to demonstrate that the hatchery fish were producing a substantial portion of the smolts leaving the Clackamas River, even while these smolts had very poor survival to adulthood. The productivity of wild winter steelhead, measured as the production of both smolt and adult offspring per parent, declined substantially with the onset of the summer steelhead hatchery program. We conclude that the natural-spawning hatchery adults failed to produce adult offspring but still occupied natural spawning habitat and produced juveniles that occupied natural rearing habitat and thereby depressed the productivity of the wild population through density-dependent mortality.

QUOTES FOR THE TEXT: Previous studies of the ecological risks and influences that hatchery fish may impose on wild fish focused on interactions between hatchery and wild juveniles immediately after the hatchery fish were released. This study demonstrates that the ecological risks caused by natural spawning by excessive numbers of hatchery adults and by the juvenile offspring they produce should also be taken into consideration.
The natural productivity of the basin, as measured by smolts produced per parent and by pre-harvest adult offspring produced per parent, promptly declined as the number of natural spawning parents abruptly increased. It appears from these relationships that the Clackamas basin has a steelhead carrying capacity of about 2,000 to 2,500 spawners. The number of adults passed into the natural spawning areas above North Fork Dam exceeded 2,500 fish 65% of the time after the start of the “Skamania” hatchery program, and in some years exceeded 4,500 adults, which are abundance levels not observed prior to the hatchery program.
Fewer smolts from wild parents translate into fewer adult offspring per wild parent. The number of adult offspring produced per wild winter-run parent dropped to very low levels immediately after the start of the “Skamania” hatchery program and remained below replacement in most years. The wild population had been able to substantially increase the number of adult offspring per parent when population sizes fell below 2,000 prior to the implementation of the hatchery program. Likely poor ocean survivals during the 1980s also influenced these results, producing a double impact of lower freshwater productivity and lower smolt to adult survivals. Meanwhile, the number of adult offspring produced per summer-run parent was very low throughout the program, consistent with our earlier observations of very few unmarked summer steelhead in the basin.
The hatchery parents were able to produce smolt offspring, although they did so with less success than wild parents. However, they were very unsuccessful at producing adult offspring. The wild Clackamas steelhead remained much more successful at natural reproduction than the hatchery fish, even when their productivity was substantially depressed. The hatchery parents produced only 66% and 51% as many smolts per parent as did the wild fish, and only 3% and 34% as many pre-harvest adult offspring per parent as did the wild fish.
It is remarkable, but evident in this study, that the hatchery fish were able to spawn and produce smolts, the two life stages that are captive in the hatchery program. The biggest die-off occurred from smolt to adult, the life stages of hatchery fish that occurs in the natural environment.
The decrease in wild fish productivity was not due to genetic effects caused by interbreeding in this case because of the different life histories of the hatchery and wild adults. We conclude that the “Skamania” hatchery adults occupied spawning habitats and their juveniles occupied freshwater rearing habitats thereby impacting the productivity of wild steelhead through density-dependent mortality.

GENETIC EFFECTS OF TRANSFERING FISH

Waples, R.S., In press. Pages 51-69 in D. Philip, editor. Proceedings of the World Fisheries Congress, Theme 3. Oxford and IBH Publishing Co., New Delhi.

ABSTRACT: Genetic variation can be partitioned into differences between individuals within populations, differences between populations within species, and differences between species or higher taxa. Although species-level differences have received the most attention with respect to biodiversity, the hierarchical levels are not independent. For example, just as population viability depends on maintaining genetic variation among individuals, so to may the long-term viability of a species depend on conserving multiple, semi-independent populations (or stocks). In addition to contributing to the erosion of between-population genetic diversity, stock transfers may lead to reduced population fitness through outbreeding depression. These risks are discussed with examples involving freshwater and anadromous fishes in North America. Studies of largemouth bass provide perhaps the clearest evidence of the negative effects of stock transfers on the fitness of local populations. Further more, genetic markers used in these studies demonstrate substantial introgression of foreign genes into local populations, indicating that the effects of stock transfers may be long lasting, if not permanent. In Pacific salmon, local populations exhibit considerable diversity in life history traits such as age structure; ocean migration patterns; and time of spawning, emergence, and outmigration. This diversity can be expected to buffer total productivity for the species against periodic or unpredictable changes in the environment. Extensive stock transfers, involving the exchange of eggs among hatcheries and intentional or unintentional release of hatchery fish into the wild, have contributed to a decline in between-population genetic diversity of these species.

ECOLOGICAL INTERACTIONS BETWEEN WILD AND HATCHERY SALMONIDS

Einum, Sigurd and Ian A. Fleming. 2001. Nordic J. Freshw. Res. 75:56-70.

ABSTRACT: The common management practice of introducing artificially produced fish into wild populations has raised concerns among fishery biologists. In part, these concerns arise from the observation that hatchery-produced fish commonly differ from wild fish in ways that may influence ecological interactions between them. In this review, we use a meta-analytical approach to provide quantitative tests for such differences and show that the hatchery rearing of salmonids results in increased pre-adult aggression, decreased response to predators, and decreased survival. Changes in growth rates are common, but less consistent. Changes in other fitness related traits such as migration, feeding, habitat use and morphology also occur. Based on the presented evidence we conclude that differences between hatchery-reared and wild fish may have negative implications for the success of stocking programs. A number of studies reporting population responses to stocking support this, suggesting that the performance of hatchery fish and their interactions with wild fish is of such a character that many of the current stocking practices may be detrimental to the recipient populations.

TEXT QUOTES: Genetic changes due to relaxed and/or altered selection are likely to accumulate in stocks being cultured over multiple generations (e.g., when brood stock is consistently chosen from adults originating from hatchery produced smolts). Multi-generation hatchery stocks are thus likely to differ more from wild fish than first generation stocks where most of the changes are likely to be of environmental origin.
Studies suggest that hatchery fish differ from wild fish in levels of aggression and predator avoidance behavior. In most studies, the effect of artificial rearing appears to result in an increase in levels of aggression (5 out of 9 studies). In the three studies where the origin of the difference was predominately environmental, hatchery fish were consistently more aggressive than wild fish.
Hatchery fish do differ from wild fish in levels of anti-predator behavior. Hatchery fish are observed to differ from wild fish in their timing of migration, which may influence both their susceptibility to predation and their energetic costs (i.e. due to different temperature and flow regimes). If this effect on timing of migration also influences breeding time, offspring survival may be compromised due to inappropriate emergence timing from nests.
Hatchery populations may also differ from wild populations in feeding behavior and habitat use.
Salmonid populations exhibit differences in morphological traits, and these differences have been suggested to result form local adaptations to environmental conditions. Furthermore, morphological traits are important determinants of breeding success. Thus any deviation in morphology from the local population may be expected in decreased fitness.
If hatchery fish differ from wild fish in so many respects, how successful are the released fish likely to be in the wild? Assuming that the wild populations have undergone natural selection for ten thousand years (since the end of the last ice age) to become adapted to the local environment, one would predict that these changes in fitness-related traits are a potential problem for released fish, and may influence their ability to survive and reproduce. Their performance in the wild should therefore be expected to be inferior to that of wild fish, a pattern that is commonly observed.
The success of hatchery-produced fish after release appears to be constrained by phenotypic divergence from their wild conspecifics. This is not surprising given the potential importance of local differences among wild salmonid populations in fitness-related traits and the evidence we have presented concerning the effects of hatchery environments on development and selection.
One might speculate that hatchery fish are to some degree able to displace naturally produced fish (in streams), but that they are unable to cope with the high cost associated with this behavior in terms of risk of starvation or predation. If so, net fish production may actually decrease as a result of stocking.
Releases of hatchery fish can also attract predators and thus may cause the intensity of predation on naturally produced fish to increase.
The effects that released hatchery fish can impose on naturally produced fish should make us cautious toward implementing stocking programs to compensate for habitat degradation and to increase fisheries. Indeed, under certain scenarios, theoretical models suggest that long-term stocking may lead to extinction of the native population. Existing empirical studies clearly show that fish density in stocked streams may not show the desired positive response to releases. In fact, in some cases a negative trend in population density has been associated with releases. Perhaps the best evidence for such an effect comes from a controlled study where populations of coho salmon were monitored for five years in 15 stocked and 15 unstocked streams. Stocked streams had higher densities of juveniles after stocking, but the number of adults returning to the two types of streams did not differ. Furthermore, spawning success of released fish was reduced, causing a lower density of juveniles in the stock streams than in the unstocked ones one generation later.
The performance of hatchery fish and their interactions with wild fish appear to be of such a character as to suggest that many of the current stocking practices may be detrimental to the recipient population. The present synthesis should incite caution in our attempts to mitigate negative effects of habitat degradation by releasing hatchery -produced fish.
A critical question we might ask ourselves is whether something can be done to avoid negative ecological effects of stocking. The answer to this question is yes and no. Better broodstock collection and mating protocols, more-natural rearing conditions, wild-fish-friendly release strategies and more focus on local broodstocks can improve the quality of hatchery fish released and reduce their impacts on wild fish. Released juveniles should be within the size range of wild juveniles, if not of a similar size distribution. The number of fish released should not exceed the carrying capacity of the environment, which varies spatially within the river and through time.
However, as Waples points out, it is a myth to believe that these changes will make the problems disappear altogether. This is because (1) environmental and genetic changes to fish in hatcheries cannot be avoided entirely; and (2) many of the risks are negatively correlated, so efforts to reduce one risk simultaneously increases another. Clearly we need to, first and foremost, be cautious in our use of hatcheries, particularly when releases are to be used in supplementing wild populations.
ABILITY OF HATCHERY SALMONIDS TO CONTRIBUTE TO THE NATURAL PRODUCTIVITY OF WILD POPULATIONS

Fleming, Ian A. and Erik Peterson. 2001. Nordic J. Freshw. Res. 75: 71-98.

ABSTRACT:
The success and implications of hatchery release programmes are intimately tied to the reproductive capabilities of the hatchery fish in the wild. Moreover, reproductive interactions are important in understanding the ecological and genetic threats that hatchery fish may pose to wild populations. Reproductive success is a key to self-sustainability, shaping natural and sexual selection, and influencing the genetic diversity of populations. In this paper, we review the determinants of breeding success in natural populations and the implications of parental traits and decisions for offspring survival and success. We then address how rearing and release programmes affect the reproductive traits and performance of fish. A review of such programmes reveals that in the few cases where adequate assessments have been made released fish frequently fail to attain self-sustainability and/or contribute significantly to populations. Clearly, new approaches based on sound scientific research are needed and these need to be tailored specifically to the management objectives.

INTRODUCTION:
Deliberate releases of salmonid fishes appear to take two main forms: (1) fisheries releases to increase population size for fisheries; and (2) conservation releases to save populations at risk of extinction…
One of the main premises/goals upon which many of the above concepts of fish releases are built upon is that they can provide a positive long-term benefit to natural populations. Yet, there appears to have been little or no attempt to find out whether this goal is achieved.
The role of fish releases in the conservation of wild salmon populations is intimately linked to understanding the dynamics of breeding and ultimately, reproductive success between wild and hatchery released salmon. The aim of this paper is to review the determinates of breeding success and its close link with offspring success (reproductive success) in salmonid fishes…
We examine the close relation between reproductive success and the desired goals of release programs, and how they may affect the reproductive traits and performance of fish. Finally, we provide an analysis of release programs where direct and indirect information about the reproductive success of released salmonids and their potential effect on natural productivity exist.

REPRODUCTIVE PATTERNS OF RELEASED FISH:
Hatchery adults appear to show reduced expressions of morphological characters important during breeding, such as secondary sexual characters (color, kype). Such reduced expressions of secondary sexual characters can have negative consequences for natural breeding success.
For hatchery females in competition with wild females, indicators of inferior competitive ability include delays in the onset of breeding, fewer nests, and greater retention of eggs. Ultimately, the breeding success of hatchery fish is frequently inferior to that of wild females.
The breeding behavior of males appears more strongly affected by hatchery rearing than that of females, reflecting the greater intensity of selection on male competitive ability during this period. Hatchery males tend to be less aggressive and less active courting females and ultimately achieve fewer spawnings than wild males. Hatchery males suffer more from inferior breeding performance than hatchery females. This pattern also appears to carry over into the wild, where gene flow between cultured and wild salmonids is sex based…

REPRODUCTIVE SUCCESS OF WILD AND HATCHERY FISH: The most common form of release program is aimed at the supplementation of wild populations, i.e. the intentional integration of hatchery and natural production, with the goal of improving the status of an existing natural population. Such integration, however, entails significant ecological and genetic risks to the wild population. …Despite large-scale releases…the supplementation programs must be deemed failures. In none of the studies reporting significant introgression, is there information on whether the release program resulted in improved natural production of the population.
All ecological evidence points to diminished lifetime reproductive success and abilities of hatchery-released salmonids to contribute to natural productivity… released fish have approximately a tenth the ability of wild fish to contribute to natural productivity.

CONCLUSIONS:
If the goal is to re-establish or rebuild wild populations for conservation purposes (i.e. conservation releases), current hatchery practices appear to result in competitively and reproductively inferior fish that limit their effectiveness. Long-term application of such releases will moreover inhibit local adaptation and thus natural productivity. On the other hand, if the goal is to supplement wild populations to increase fisheries (i.e. fisheries releases) while reducing impacts on the wild populations, such reproductive inferiority could be advantageous, limiting the negative effects of introgression. However, the threats of ecological interference and altered selection regimes associated with the introduction of hatchery fish remain.
Poorly managed hatchery programs can alter or even destroy biological diversity of species/populations.