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Age‐at‐release, size, and maturation status influence residualism in hatchery steelhead trout, Oncorhynchus mykiss
... The present study evaluated in-culture performance and reproductive contributions from conservation hatchery practices that differed in important ways from typical programs, including (i) naturally spawned embryos were collected, (ii) juveniles were reared to smolt in two years rather than one, (iii) rearing occurred at two different facilities, and (iv) post-smolt rearing continued in both fresh and seawater until final sexual maturity when the fish were released. The trade-offs associated with embryo collections and age-2 smolt rearing have been fairly well detailed in previous studies (Tatara et al. 2019), as have details of the reproductive behavior of captively reared anadromous salmonids Venditti et al. 2013) and trade-offs associated with multiple different release strategies for endangered salmon populations (Johnson et al. 2020). The present study adds that (i) ARG females contributed to production of parr and smolts, (ii) presmolt and post-smolt culture environments (fresh water vs. seawater) influence survival, maturation, and body size, (iii) body size at maturation was positively correlated with reproductive performance of released adults, and (iv) ARG offspring exhibited early marine survival that was roughly the same as offspring of naturally returning parents. ...
Conservation hatcheries designed to aid in recovery of imperiled fish population often implement atypical rearing and release strategies. We evaluated a conservation hatchery program for steelhead (Oncorhynchus mykiss) that hydraulically removed naturally spawned eggs, and captively reared them in different freshwater hatcheries to the smolt stage, and reared smolts in both freshwater and seawater to sexual maturity, before releasing the sexually maturing adults onto the spawning grounds. The adult steelhead added to the spawning population, accounting for most of the adults observed during snorkel observations. They produced 32% of the juvenile offspring sampled, and females were 2.9 times more successful than males. Reproductive success was positively correlated with female body size, which was influenced by pre-smolt and post-smolt rearing conditions and their effects on growth rate and age-at-maturity. Juvenile offspring of the released adults showed size and age differences from offspring of naturally returning steelhead, but exhibited very similar early marine survival rates.
... Genetic males were identified by the presence of the male sex determining gene, sdY [32], following the procedure described in [33]. Briefly, genomic DNA was PCR amplified using the sdY primers as described by [32]. ...
Genetic selection is often implicated as the underlying cause of heritable phenotypic differences between hatchery and wild populations of steelhead trout (Oncorhynchus mykiss) that also differ in lifetime fitness. Developmental plasticity, which can also affect fitness, may be mediated by epigenetic mechanisms such as DNA methylation. Our previous study identified significant differences in DNA methylation between adult hatchery- and natural-origin steelhead from the same population that could not be distinguished by DNA sequence variation. In the current study, we tested whether hatchery-rearing conditions can influence patterns of DNA methylation in steelhead with known genetic backgrounds, and assessed the stability of these changes over time. Eyed-embryos from 22 families of Methow River steelhead were split across traditional hatchery tanks or a simulated stream-rearing environment for 8 months, followed by a second year in a common hatchery tank environment. Family assignments were made using a genetic parentage analysis to account for relatedness among individuals. DNA methylation patterns were examined in the liver, a relatively homogeneous organ that regulates metabolic processes and somatic growth, of juveniles at two time points: after eight months of rearing in either a tank or stream environment and after a subsequent year of rearing in a common tank environment. Further, we analyzed DNA methylation in the sperm of mature 2-year-old males from the earlier described treatments to assess the potential of environmentally-induced changes to be passed to offspring. Hepatic DNA methylation changes in response to hatchery versus stream-rearing in yearling fish were substantial, but few persisted after a second year in the tank environment. However, the early rearing environment appeared to affect how fish responded to developmental and environmental signals during the second year since novel DNA methylation differences were identified in the livers of hatchery versus stream-reared fish after a year of common tank rearing. Furthermore, we found profound differences in DNA methylation due to age, irrespective of rearing treatment. This could be due to smoltification associated changes in liver physiology after the second year of rearing. Although few rearing-treatment effects were observed in the sperm methylome, strong family effects were observed. These data suggest limited potential for intergenerational changes, but highlight the importance of understanding the effects of kinship among studied individuals in order to properly analyze and interpret DNA methylation data in natural populations. Our work is the first to study family effects and temporal dynamics of DNA methylation patterns in response to hatchery-rearing.
The effects of domestication selection on fitness are of serious concern for hatchery‐reared anadromous salmonids, which often experience selection for rapid growth and associated deviations from natural agonistic and feeding behaviors. Consequently, steelhead (Oncorhynchus mykiss) hatchery programs with recovery or conservation goals may change fish culture practices to minimize domestication selection. We raised steelhead from a common broodstock to smolt at age 1 or age 2 by manipulating ration (age 1 high ration, age 2 low ration). It is probable that the high rations used to raise age‐1 smolts and the reduced rations used to produce age‐2 smolts could result in very different behavioral tactics and social dynamics of competition in hatchery tanks. The study investigated how feeding rate (proportion of presented food items successfully captured) and relative competitive ability (ability to monopolize food items in small groups) of age‐1 and age‐2 steelhead corresponded to feeding location (surface or bottom) and growth rate in hatchery rearing tanks. The age‐1 treatment had lower feeding rate than the age‐2 treatment. Feeding rate was positively correlated with both body size and with growth rate in rearing tanks at both rations. Age‐2 steelhead were more likely to be detected at a single feeding location than age‐1 fish, which were more frequently detected at both locations. More competitive age‐1 fish were more frequently detected at both feeding locations and less competitive fish at only one location. Relative competitive ability was not associated with feeding location in the age‐2 treatment, nor with growth rate in either treatment. Age‐2 steelhead detected only at the bottom or at both feeding locations had higher growth rates than those detected only at the surface, suggesting greater scramble competition near the point of food delivery under the restricted ration. Feeding location was not associated with growth rate in the age‐1 treatment. The results indicate that ration directly affects feeding rate and that ration and relative competitive ability interact to influence feeding rate. Because feeding rate was positively associated with growth rate at both ration levels in hatchery tanks, behaviors associated with feeding motivation may be an important trait under selection in salmonid hatcheries.
Female steelhead trout (Oncorhynchus mykiss) reared for one year (traditional, ‘S1’) and two years (experimental ‘S2’) in captivity in the Methow River Basin, WA, produced very similar numbers of offspring in replicate spawning channels over three consecutive years. In contrast, S1 anadromous males outcompeted S2 males for access to nesting females, and as a result, produced significantly more offspring. Male dominance was positively associated with body mass, but body mass did not account for differences between S1 and S2 males. Much smaller precocious S2 males that matured during rearing in hatchery raceways sired offspring in all six breeding groups. Contributions from precocious males were nearly always the result of sneak spawning events, although on rare occasions, precocious males were able to stimulate females to spawn in the absence of an anadromous male. Similarities in female breeding success suggest that S1 and S2 hatchery steelhead should exhibit similar productivity under natural conditions, and S1 male steelhead may result in greater rates of gene flow from hatchery to natural populations.
Steelhead Trout (Oncorhynchus mykiss) display a varied life-history, including precocious male maturation at age-1 or age-2. In wild fish, precocious male maturation represents an important component of a diverse life-history portfolio. In hatchery programs, however, it is undesirable if rearing practices increase rates of early male maturation and reduce numbers of anadromous male adults. Our study aimed to develop endocrine and molecular markers for identifying males at early stages of maturation in the spring (prior to smolt release) and evaluated the potential use of these markers for quantifying early male maturation rates at a hatchery scale. In a laboratory study, Skookumchuck winter-run Steelhead Trout were reared at a high growth rate in order to increase the occurrence of precocious male maturation. Fish were lethally sub-sampled in February, prior to the time of smolt release; in May, at the time of smolt release; and in September, when 1+ age maturing males that would spawn the following spring were clearly identifiable based solely on gonadosomatic index (GSI). In February and May samples, we measured GSI, plasma 11-ketotestosterone (11KT), mRNAs for pituitary follicle stimulating hormone (fshb) and luteinizing hormone (lhb) beta subunits, and analyzed stage of spermatogenesis by testis histology. Additionally, in May, we measured testis anti-Müllerian hormone (amh) and insulin-like growth factor 3 (igf3) mRNA. Our primary goal was to evaluate the aforementioned maturation indices for their efficacy in forecasting the proportion of fish initiating early male maturation in the spring (approximately 1 year prior to spermiation), compared to the proportion that actually matured. Combining measures of GSI, plasma 11KT, and pituitary fshb and lhb mRNA expression provided a useful, but conservative, estimate of the proportion of males initiating maturation in the spring (21%) compared to the proportion that were ultimately destined to mature (37%) the following spring. These results suggest that maturation may be less synchronous than previously appreciated and some males may have initiated maturation after our census in May.
Hatchery programs for anadromous salmonids, including steelhead trout Oncorhynchus mykiss that are designed to aid recovery of natural populations require locally-derived, natural-origin broodstock. In such programs, achieving smoltification size thresholds may require extending hatchery rearing beyond age-1. We compared out-migration survival and travel rate of 142,990 age 1 (S1) and age 2 (S2) steelhead smolts implanted with passive integrated transponder (PIT) tags over five release years at Winthrop National Fish Hatchery (WNFH, Okanogan County, WA). A S2 rearing cycle produced larger smolts with more uniform size distributions, resulting in higher survival during the first portion of their out-migration than S1 smolts in three of five release years. The S2 smolts migrated more rapidly to the ocean than S1 smolts in all years except 2011, and arrived in the Columbia River estuary an average of 5.4 d earlier than the S1 smolts. S1 steelhead that did not leave during the volitional release were subsequently forced from the hatchery to measure their survival. These fish were smaller and had survival rates that were 2.3–66.3 times lower than S1 steelhead that left the hatchery on their own. The same was true for S2 steelhead, but the magnitude of the survival difference between migrants and fish forced from the raceways was less variable and ranged from 2.5–4.6 fold. We conclude that S2 rearing can be a successful strategy for producing smolts from local natural-origin broodstock with out-migration survival and travel times that are equivalent or better than those of S1 smolts produced from nonlocal broodstock.
Received 25 Jul 2016 accepted 31 Mar 2017 revised 27 Mar 2017
We investigated the effects of nonmigrant (residual) juvenile hatchery steelhead
(anadromous rainbow trout Oncorhynchus mykiss) on growth of wild rainbow trout and juvenile
spring chinook salmon O. tshawytscha to examine how increased densities of residual hatchery
steelhead might affect the growth of preexisting wild rainbow trout and chinook salmon. We used
screened enclosures in a natural stream to examine food utilization and physiological stress, factors
that might affect fish growth. The presence of residual hatchery steelhead led to reduced growth
of wild rainbow trout (1993: P = 0.019; 1994: P = 0.020) but not of spring chinook salmon (P
= 0.360). Enclosures did not reduce the total number of food items available but did influence
the species composition of aquatic and terrestrial invertebrates. The food habits of paired and
unpaired fish differed; however, the power of those tests was low. Cortisol level, a measure of
physiological stress, did not differ between paired and unpaired fish held in enclosures. Cortisol
levels were significantly lower in fish confined for 42 d than in wild fish outside the enclosures
at the end of the experiment. Our results suggest that adverse effects on wild rainbow trout growth
resulting from high densities (a doubling) of residual juvenile steelhead from hatchery releases
may be significant.
Steelhead trout (Oncorhynchus mykiss) reared under two different regimes: high food ration for 1 year (S1; typical strategy) or low ration for 2 years (S2) were subjected to a seawater challenge during the corresponding spring outmigration period. The S1 smolts were smaller and suffered greater seawater challenge mortality (23.9% compared with 0.7% for the S2 smolts) that was significantly and negatively related to body size. Heritability of body size was similar for the two treatments during the parr stage (fork length: S1 = 0.181, S2 = 0.245; mass: S1 = 0.372; S2 = 0.447), but higher for the S1 treatment during the smolt stage for length (S1 = 0.212, S2 = 0.002) and body mass (S1 = 0.145, S2 = 0.015). Strong family effects for both traits and significant family by environment interactions for parr mass and smolt length indicated significant phenotypic plasticity. A genetic response to size-selective mortality caused by insufficient growth opportunity in the S1 treatment is plausible and may affect fitness in the natural environment through effects on correlated traits.
The genetic underpinnings associated with the earliest stages of plant and animal domestication have remained elusive. Because a genome-wide response to selection can take many generations, the earliest detectable changes associated with domestication may first manifest as heritable changes to global patterns of gene expression. Here, to test this hypothesis, we measured differential gene expression in the offspring of wild and first-generation hatchery steelhead trout (Oncorhynchus mykiss) reared in a common environment. Remarkably, we find that there were 723 genes differentially expressed between the two groups of offspring. Reciprocal crosses reveal that the differentially expressed genes could not be explained by maternal effects or by chance differences in the background levels of gene expression among unrelated families. Gene-enrichment analyses reveal that adaptation to the novel hatchery environment involved responses in wound healing, immunity and metabolism. These findings suggest that the earliest stages of domestication may involve adaptation to highly crowded conditions.
The explosion of information on the distribution and impacts of whirling disease in the United States during the last decade has changed the way in which we view Myxobolus cerebralis. However, even a cursory review of whirling disease literature reveals that many of our concerns today have been expressed at some previous time in the history of our experience with this parasite. From the first description of M. cerebralis in Germany in 1893, it was recognized that whirling disease could severely affect the growing trout farming industry. During the first half of this century M. cerebralis was disseminated throughout Europe, especially following WWII when live rainbow trout Oncorhynchus mykiss were transferred freely. Between 1950 and 1970, the parasite began to appear at trout farms on other continents, and it was in the late 1950s that whirling disease first emerged in the United States. Nearly all reports of detection, both here and in Europe, were associated with artificial rearing facilities. Until the 1980s, the only references reporting infections in natural populations of salmonids are from Finland, Russia, and Michigan, and the reported infections were usually light. Clinical whirling disease was largely associated with culture of trout in earthen ponds, where the infective agent concentrated. In the period between 1970 and 1990, there were increasing reports of the parasite in hatcheries throughout Europe and the United States. In Europe, the perspective after many years of living with whirling disease was that eradication was not possible in most cases, but that we knew enough to reduce infection levels below the point where clinical disease occurs. In the United States, reports of whirling disease in hatcheries were often followed by destruction of any fish on the facility, but as it became apparent that proper management could reduce infection levels, and as there appeared to be no effects outside the bounds of the hatchery, these standards were relaxed. However, in the 1990s, clinical whirling disease was reported in free-ranging trout populations in Colorado and Montana, causing us, once again, to rethink how this disease can be controlled and managed.
We reared juvenile Oncorhychus mykiss with low and high standard metabolic rates (SMR) under alternative thermal regimes to determine how these proximate factors influence life histories in a partially migratory salmonid fish. High SMR significantly decreased rates of freshwater maturation and increased rates of smoltification in females, but not males, after 1 year of rearing. Warmer water temperatures significantly decreased rates of freshwater maturation and increased rates of smoltification in both sexes. Variation in individual growth influenced the probability of adopting anadromy or freshwater residency as life histories, but produced paradoxical results. Individuals with the highest growth performance within their respective temperature treatments had a higher probability of freshwater maturation, but warmer temperatures decreased freshwater maturation despite significantly increasing somatic growth. Whole-body lipid content was significantly lower for fish reared in the warm temperature treatment, which may explain the decreased probability of freshwater maturation for individuals exposed to warmer temperatures. Our results indicate that changes in somatic growth induced by altered thermal regimes can influence the relationship between body size and the probability of maturation. Accordingly, somatic growth may not be a robust predictor of shifts in the prevalence of anadromy and residency in partially migratory salmonids when compared across thermal regimes.
Oncorhynchus mykiss form partially migratory populations with anadromous fish that undergo marine migrations and residents that complete their life cycle in fresh water. Many populations’ anadromous components are threatened or endangered, prompting interest in understanding ecological and evolutionary processes underlying anadromy and residency. In this paper, we synthesize information to better understand genetic and environmental influences on O. mykiss life histories, identify critical knowledge gaps, and suggest next steps. Anadromy and residency appear to reflect interactions among genetics, individual condition, and environmental influences. First, an increasing body of literature suggests that anadromous and resident individuals differ in the expression of genes related to growth, smoltification, and metabolism. Second, the literature supports the conditional strategy theory, where individuals adopt a life history pattern based on their conditional status relative to genetic thresholds along with ultimate effects of size and age at maturation and iteroparity. However, except for a generally positive association between residency and high lipid content plus a large attainable size in fresh water, the effects of body size and growth are inconsistent. Thus, individuals can exhibit plasticity in variable environments. Finally, patterns in anadromy and residency among and within populations suggested a wide range of possible environmental influences at different life stages, from freshwater temperature to marine survival. Although we document a number of interesting correlations, direct tests of mechanisms are scarce and little data exist on the extent of residency and anadromy. Consequently, we identified as many data gaps as conclusions, leaving ample room for future research. © 2015, National Research Council of Canada. All rights reserved.
Wild steelhead (Oncorhynchus mykiss) returning to the Hood River in Oregon, USA, show a strongly female-biased sex ratio (average of 63 % female from brood years 1992 to 2004) while first-generation hatchery steelhead (created using local, wild broodstock) display an even sex ratio (51 % female). We considered four hypotheses to explain the difference in sex ratio between populations. First, it is well established that wild male O. mykiss adopt the resident (non-anadromous) life history phenotype at a higher rate than do females, and that the propensity to become resident is under genetic and environmental influence. Therefore, the simplest explanation for the difference in sex ratio between anadromous wild and hatchery fish is that hatchery males adopt the resident life history at a lower rate than do wild males. However, alternative explanations include (1) sex reversal of female hatchery fish to phenotypic males, (2) selection against hatchery females or (3) selection against wild males. The possibility of sex reversal in the hatchery was of particular interest given increased temperature has been shown to skew sex ratios to a male bias. Using a Y-chromosome specific marker (OmyY1 locus) and samples of wild and hatchery fish from various life stages, we were able to reject alternative hypotheses 1, 2 and 3. Hatchery fish were sampled at three life stages (onset of exogenous feeding, 1-year of age and returning adult). Phenotypic and chromosomal sex matched in all 1-year old and adult hatchery samples. Therefore, we see no evidence for sex reversal in the hatchery population. Furthermore, hatchery fish at all three life stages exhibited a 50:50 chromosomal (OmyY1 marker) sex ratio. Therefore, selection against hatchery females while in captivity or after release can be ruled out. The chromosomal sex ratio in a sample of wild smolts was female-biased and matched the sex ratio in returning adults from the same cohort. Therefore, we can also rule out selection against wild males at sea. Given no evidence for sex reversal or selection against either sex it seems most plausible that the greater female bias in wild, compared to hatchery, steelhead from the Hood River results from differential life history expression in males. Wild males appear to become resident (non-anadromous) at a higher rate than do hatchery males.
Hatchery-reared steelhead Oncorhynchus
mykiss that do not emigrate as smolts shortly after release
may harm wild fish communities through ecological interactions.
We used systematic, stratified snorkeling surveys
to document the relative abundance of wild rainbow
trout (nonanadromous O. mykiss), bull trout Salvelinus
confluentus, and westslope cutthroat trout O. clarki lewisi
as well as the upstream limit of residual hatchery steelhead
(hatchery-reared steelhead that had failed to emigrate
by June 1). Our objective was to determine whether
residual hatchery steelhead had migrated upstream from
their release point into an area containing westslope cutthroat
trout and a threatened population of bull trout.
Hatchery steelhead made up a larger proportion of the
salmonid community in the sites near their release location
and constituted a lower proportion as distance
upstream from the release location increased. However,
residual hatchery steelhead had migrated over 12 km
upstream into an area containing westslope cutthroat
trout and a threatened stock of bull trout.
Adaptation of plants or animals to captivity is a risk associated with any captive breeding program that has the intent of returning organisms to the wild. The risk is particularly acute for species that are captively bred and released on a large scale, as is the case for many species of fish. Several studies, particularly in salmonids, have reported rapid adaptation of populations to captivity, but the mechanisms of such adaptations are not always clear. We evaluated a large three-generation pedigree of an artificially supplemented salmon population, and found that the fish with the highest reproductive success in captivity produce early maturing male offspring that have lower than average reproductive success in the wild. In contrast to an earlier study of steelhead trout, we found little evidence that parental origin of the captive spawners influenced the subsequent reproductive success of their naturally spawning progeny.
We classified juvenile hatchery summer steelhead Oncorhynchus mykiss released from Wells Hatchery, Washington, from three brood years (2002–2004) as those that migrated volitionally (VM) from rearing ponds or as those that were forced out of rearing ponds after volitional migration concluded (NM). Fish were implanted with PIT tags prior to release and we used recreational angling equipment to recapture tagged fish to estimate the relative contribution rates of VM and NM release groups to the stream-resident population of juvenile hatchery summer steelhead in the Twisp River. We also evaluated the survival for each group from release to McNary Dam, and from release to adult return (SAR) at Bonneville and Wells dams on the Columbia River. Overall, we estimated that 82% of stream-resident hatchery juvenile summer steelhead originated from releases of NM fish. The probability of survival from release to McNary Dam was significantly greater for VM groups (mean, 0.4817; SE, 0.023) than for NM groups (mean, 0.2182; SE, 0.021) within each year. The mean SAR to Bonneville and Wells dams was 1.54% and 1.26%, respectively, for VM fish and 0.37% and 0.32%, respectively, for NM fish; the differences were significant between groups within each year. As an index of release strategy performance, VM releases resulted in one stream-resident fish recaptured for every 7.8 adults returned, while NM releases produced one stream-resident fish recaptured for every 0.48 adults returned. These results suggest that managers employ a volitional release strategy to significantly reduce the abundance of stream-resident juvenile hatchery steelhead by not releasing NM fish into waters inhabited by anadromous fishes, thereby reducing negative ecological interactions between hatchery residual steelhead and wild salmonids at little cost to adult returns.Received February 25, 2013; accepted July 8, 2013
In partially migratory species, such as Oncorhynchus mykiss, the emergence of life history phenotypes is often attributed to fitness trade-offs associated with growth and survival. Fitness trade-offs can be linked to reproductive tactics that vary between the sexes, as well as the influence of environmental conditions. We found that O. mykiss outmigrants are more likely to be female in nine populations throughout western North America (grand mean 65% female), in support of the hypothesis that anadromy is more likely to benefit females. This bias was not related to migration distance or freshwater productivity, as indicated by latitude. Within one O. mykiss population we also measured the resident sex ratio and did not observe a male bias, despite a high female bias among outmigrants in that system. We provide a simulation to demonstrate the relationship between sex ratios and the proportion of anadromy and show how sex ratios could be a valuable tool for predicting the prevalence of life history types in a population.
Abstract – Differential rates of anadromy between males and females are common in partially migratory salmonid populations, but this pattern is not fully clear for Oncorhynchus mykiss (rainbow trout/steelhead) from the limited but mixed data available. In particular, there are very few data on sex ratios of juvenile and nonanadromous (resident) fish to help assess sex composition of various life stages and life‐history types. We used a recently developed Y‐chromosome genetic marker to assess sex ratio of stream‐dwelling (i.e., juvenile and nonanadromous) O. mykiss in a small coastal basin in central California, USA. We analysed 384 samples collected from three contiguous study reaches over 3 years. Sex ratio was 1:1 among juvenile‐sized O. mykiss (O. mykiss and other species.
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.
Avoiding negative effects of competition from released hatchery salmonids on wild fish is a primary concern for recovery efforts and fisheries management. Several factors affect competition among juvenile salmonids including: (1) whether competition is intra- or interspecific, (2) duration of freshwater cohabitation of hatchery and wild fish, (3) relative body size, (4) prior residence, (5) environmentally induced developmental differences, and (6) fish density. Intraspecific competition is expected to be greater than interspecific because of greater niche overlap between conspecific hatchery and wild fish. Competition is expected to increase with prolonged freshwater cohabitation. Hatchery smolts are often larger than wild, and larger fish are usually superior competitors. However, wild fish have the advantage of prior residence when defending territories and resources in natural streams. Hatchery-induced developmental differences are variable and can favor both hatchery and wild fish. Although all these factors influence competitive interactions, fish density of the composite population (wild + hatchery fish) in relation to habitat carrying capacity likely exerts the greatest influence. The extent of competition and relative competitive ability of wild and hatchery fish can be determined by additive and substitutive experimental designs, respectively, and the limited body of substitutive experiments suggests that the relative competitive ability of hatchery and wild fish is approximately equal when measured as growth. Conducting substitutive experiments becomes difficult as the spatial and temporal scales increase. Large-scale experiments comparing supplemented and control reaches or streams hold some promise for quantifying the effects of released hatchery fish on wild fish behavior, growth and survival.
Differences in selection regimes between hatchery and natural environments and environmental stimuli, among other factors, have the potential to cause differences in predator avoidance ability between hatchery and wild steelhead trout fry (Oncorhynchus mykiss). In two separate laboratory experiments, fry raised from eggs of wild Quinault River steelhead trout survived predation by prickly sculpin (Cottus asper) significantly better than size-matched offspring of a locally derived hatchery population, which were reared under similar conditions. Wild fry also survived predation better than hatchery fry in natural stream enclosures over a 3-day test period. Experience, in the form of 50-min visual exposure to sculpin predation on "sacrificial" steelhead trout, improved the ability of fry from both populations to avoid predation by;sculpin. Wild-experienced fry were eaten in the fewest number of trials followed by wild-naive, hatchery-experienced, and hatchery-naive fry. The results of this study are consistent with the hypothesis that innate predator avoidance ability has been negatively altered through domestication and that attempts to condition hatchery-reared steelhead to avoid predators may be limited for domesticated populations.
Competition between hatchery-reared and wild salmonids in streams has frequently been described as an important negative ecological interaction, but differences in behavior, physiology, and morphology that potentially affect competitive ability have been studied more than direct tests of competition. We review the differences reported, designs appropriate for testing different hypotheses about competition, and tests of competition reported in the literature. Many studies have provided circumstantial evidence for competition, but the effects of competition were confounded with other variables. Most direct experiments of competition used additive designs that compared treatments in which hatchery fish were introduced into habitats containing wild fish with controls without hatchery fish. These studies are appropriate for quantifying the effects of hatchery fish at specific combinations of fish densities and stream carrying capacity. However, they do not measure the relative competitive ability of hatchery versus wild fish because the competitive ability of hatchery fish is confounded with the increased density that they cause. We are aware of only two published studies that used substitutive experimental designs in which density was held equal among treatments, thereby testing for differences in competitive ability. Additional substitutive experiments will help managers to better understand the ecological risk of stocking hatchery fish.
Artificial culture may relax the selective pressures from predators, thereby altering behavioural and heart rate responses to predation risk. Culture may also impose new selection that adapts fish to confinement. Predictions from these hypotheses were tested by comparing seventh-generation farm Atlantic salmon (Salmo salar) with wild Atlantic salmon from the principal founder population of the farm strain. Wild age 1+ salmon had higher standard heart rates and showed a more pronounced flight and heart rate response to a simulated predator attack than did farmed salmon. However, wild fish were closer to the model predator at attack, which may have accentuated these differences. Both strains habituated to the threat, showing less response to the second attack than to the first. In contrast with age 1+ fish, wild age 2+ salmon had lower standard heart rates than farmed fish. Moreover, in age 2+ salmon, domestication effects were less clear and the response to predation threat considerably weaker, suggesting that environmental effects of culture override genetic effects as time in captivity increases. Domestication selection may thus alter reaction norms of farmed animals over environmental gradients and time. This should be considered when attempting to predict the consequences of release or escape of domesticated animals in the wild.
Rainbow trout (Oncorhynchus mykiss) have diverse life histories, including both freshwater-resident and anadromous "steelhead" life-history forms. Here, we demonstrate that female resident rainbow trout produce anadromous offspring that survive and return to spawn as adult steelhead. This study represents the first successful attempt to quantify steelhead production rates from female resident rainbow trout across a large watershed. Otolith microchemistry (Sr-87/Sr-86) techniques were used to determine the maternal life history (resident or anadromous) of 498 emigrating steelhead kelts in the Yakima Basin, Washington. Five geochemically distinct freshwater rearing regions were identified within the basin. All five regions were predicted to produce steelhead with resident maternal life histories. Basin-wide, 20% and 7% of steelhead collected in 2010 and 2011, respectively, had resident maternal life histories. Cross-life-history form production may be critical to persistence of anadromous life histories within partially anadromous salmonid populations, particularly in areas where anadromous fish abundance is low due to natural or anthropogenic influences.
Artificial culture may relax the selective pressures from predators, thereby altering behavioural and heart rate responses to predation risk. Culture may also impose new selection that adapts fish to confinement. Predictions from these hypotheses were tested by comparing seventh-generation farm Atlantic salmon (Salmo salar) with wild Atlantic salmon from the principal founder population of the farm strain. Wild age 1+ salmon had higher standard heart rates and showed a more pronounced flight and heart rate response to a simulated predator attack than did farmed salmon. However, wild fish were closer to the model predator at attack, which may have accentuated these differences. Both strains habituated to the threat, showing less response to the second attack than to the first. In contrast with age 1+ fish, wild age 2+ salmon had lower standard heart rates than farmed fish. Moreover, in age 2+ salmon, domestication effects were less clear and the response to predation threat considerably weaker, suggesting that environmental effects of culture override genetic effects as time in captivity increases. Domestication selection may thus alter reaction norms of farmed animals over environmental gradients and time. This should be considered when attempting to predict the consequences of release or escape of domesticated animals in the wild.
All salmonid species investigated to date have been characterized with a male heterogametic sex-determination system. However, as these species do not share any Y-chromosome conserved synteny, there remains a debate on whether they share a common master sex-determining gene. In this study, we investigated the extent of conservation and evolution of the rainbow trout (Oncorhynchus mykiss) master sex-determining gene, sdY (sexually dimorphic on the Y-chromosome), in 15 different species of salmonids. We found that the sdY sequence is highly conserved in all salmonids and that sdY is a male-specific Y-chromosome gene in the majority of these species. These findings demonstrate that most salmonids share a conserved sex-determining locus and also strongly suggest that sdY may be this conserved master sex-determining gene. However, in two whitefish species (subfamily Coregoninae), sdY was found both in males and females, suggesting that alternative sex-determination systems may have also evolved in this family. Based on the wide conservation of sdY as a male-specific Y-chromosome gene, efficient and easy molecular sexing techniques can now be developed that will be of great interest for studying these economically and environmentally important species.
After hatchery-reared salmonids are released into the wild, their survival and performance are frequently lower than those of wild conspecifics. Additionally, negative effects of hatchery fish on wild fish are cited as factors affecting the recovery of salmonid populations. Alternative hatchery rearing environments and release practices have been proposed to mitigate both problems. We investigated the postrelease growth, survival, habitat use, and spatial distribution of hatchery steelhead Oncorhynchus mykiss fry reared in conventional and enriched environments and compared their performance with that of naturally reared steelhead fry from the same parent population in two streams. Average instantaneous growth rates differed between streams but not among the three rearing groups. The survival of naturally reared fry was significantly greater than that of both types of hatchery fry (relative survival = 0.33) but did not differ between the conventional and enriched environments. Naturally reared fry grew and survived equally well regardless of the type of hatchery fry with which they were stocked. Supplementation increased fry population size in all stream sections but produced hatchery-biased populations. Steelhead fry preferred pool habitat within stream sections, but pool use was affected by an interaction between rearing environment and stream. Hatchery fry had more clumped spatial distributions than naturally reared fry, which were affected by a significant interaction between rearing type and stream. Hatchery rearing type and stream had no effect on the spatial distribution of naturally reared fry. We conclude that (1) hatchery steelhead fry released in streams grow as well as naturally reared fry but do not survive as well, (2) enriched hatchery environments do not improve postrelease growth or survival, and (3) upon release, fry raised in enriched hatchery environments affect the growth and survival of naturally reared fry in much the same way as fry reared in conventional hatchery environments.
Species interactions research was initiated in 1989 to investigate ecological interactions
among fish in response to proposed supplementation of salmon and steelhead in the upper Yakima
River basin. This is the sixth of a series of progress reports that address species interactions
research and pre-supplementation monitoring of fishes in the Yakima River basin. Data have been
collected prior to supplementation to characterize the ecology and demographics of non-target
taxa (NTT) and target taxon, predict the potential interactions that may occur as a result of
supplementation, and develop methods to monitor interactions and supplementation success.
Major topics of this report are associated with the ecology and life history of NTT, interactions
experimentation, methods for sampling, risk assessment, and risk minimization. This report is
organized into 14 chapters, with a general introduction preceding the first chapter. This annual
report summarizes data collected primarily by the Washington Department of Fish and Wildlife
(WDFW) between January 1, 1995 and December 31, 1997 in the Yakima basin, however these
data were compared to data from previous years to identify preliminary trends and patterns.
Major preliminary findings from each of the chapters included in this report are described below.
Juvenile phenotypes and fitness as indicated by survival were compared for naturally produced steelhead (Oncorhynchus mykiss), a new local hatchery stock, and an old nonlocal hatchery stock on the Hood River, Oregon, U.S.A. Although the new hatchery stock and the naturally produced fish came from the same parent gene pool, they differed significantly at every phenotype measured except saltwater age. The characteristics of the new hatchery stock were similar to those of the old hatchery stock. Most of the phenotypic differences were probably environmentally caused. Although such character changes would not be inherited, they may influence the relative fitness of the hatchery and natural fish when they are in the same environment, as selection responds to phenotypic distributions. A difference in fitness between the new hatchery stock and naturally produced fish was indicated by significant survival differences. Acclimation of the new hatchery stock in a "seminatural" pond before release was associated with a further decrease in relative smolt-to-adult survival with little increase in phenotypic similarity between the natural and hatchery fish. These results suggest that modified selection begins immediately in the first generation of a new hatchery stock and may provide a mechanism for genetic change.
Steelhead Oncorhynchus mykiss exhibit significant life history plasticity, including variation in freshwater residence time, age of smoltification, and maturation that are influenced by exceeding specific thresholds in size or body energy stores. Fish that do not reach minimum thresholds for smoltification or exceed thresholds for maturation may “residualize” in freshwater. Understanding life history diversity is important in steelhead hatchery programs. The objective of this investigation was to characterize life history diversity in Hood River, Oregon, hatchery winter-run steelhead prior to release. We used both morphological and physiological indices to assess degree of smoltification in both sexes and maturation in males. Smoltification was categorized by measuring size, visual smolt index, and gill Na⁺/K⁺-ATPase activity. All females were determined to be immature. Male reproductive development required histological staging of testes. Other indices of maturation—including gonadosomatic index, plasma 11-ketotestosterone, and pituitary fshb and lhb and testis ifg3 and amh gene expression—were also employed, with varying degrees of success. Five phenotypes were described: (1) immature male and female parr; (2) precociously mature male parr; (3) male smolts in early to mid-spermatogenesis that are likely to spawn after <1 year in the ocean; (4) males that might have attempted maturation, but failed; and (5) immature male and female smolts that could mature after >1 year in the ocean. Over three brood years, we estimated that 3–4% of the population could potentially residualize due to failure to smolt or precocious male maturation, 1–12% could mature after <1 year in the ocean (one salt male), and 84–95% could mature after >1 year in the ocean (two to three salt males and females). Based on previous studies conducted in the Hood River basin, the residualism rate estimated for this hatchery population is lower than that of naturally rearing Hood River steelhead.
This chapter describes the different aspects of the physiology of smolting salmonids. Many salmonids—the fish of the genera, Oncorhynchus, Salmo, and Salvelinus—are anadromous and undergo a distinct transformation prior to seaward migration. Several morphological and physiological changes occur during smolting. Silvering is because of the synthesis of two purines–guanine and hypoxanthine. The needle-like crystals of these substances are deposited in two distinct skin layers: one directly beneath the scales and the other deep in the dermis adjacent to the muscles. The salmonids, as many other temperate-zone animals, have a seasonally changing physiology that is manifested in the cycles of growth, precisely timed migrations, and the seasons of reproduction geared to the most favorable seasons for the birth and development of the young. There is a circannual rhythm of physiological changes associated with the parr–smolt transformation. After juvenile salmon reach a certain critical size, they become smolts with a capacity to hypoosmoregulate and grow in seawater and behavioral changes result in a downstream migration.
In the coastal British Columbia stream adult runs averaged 922 (range 209-2730) with c10% repeat spawning incidence. Females repeat spawned more than males and were more abundant as kelts, but maiden run adults were equally male and female. The proportion of males returning after 1, 2 and 3 yr in the ocean averaged 3, 62 and 35%, respectively; 58 and 42% of females returned after 1, 2 and 3 yr, respectively. Adult age structure, smolt number, and smolt size varied biennially. Adult size decreased with freshwater age, but increased with ocean age of returns. Males were larger at each ocean age. Smolts were 2-5 yr old, and freshwater age 3 was most prevalent (average 56%). Mean survival from smolt to adult was 16% (7% from 1978 cohorts to 26% from 1982 cohorts). Survival was positively correlated with smolt length and weight, but 1982 cohorts had twice the survival of other cohorts, possibly related to El Nino. On average, freshwater age was inversely related to ocean age. -from Authors
1.Life-history strategies can buffer individuals and populations from environmental variability. For instance, it is possible that asynchronous dynamics among different life-histories can stabilize populations through portfolio effects. 2.Here we examine life-history diversity and its importance to stability for an iconic migratory fish species. In particular, we examined steelhead (Oncorhynchus mykiss), an anadromous and iteroparous salmonid, in two large, relatively pristine, watersheds, the Skeena and Nass, in northwestern British Columbia, Canada. We synthesized life-history information derived from scales collected from adult steelhead (N = 7227) in these watersheds across a decade. 3.These migratory fishes expressed 36 different manifestations of the anadromous life-history strategy, with 16 different combinations of freshwater and marine ages, 7.6% of fish performing multiple spawning migrations, and up to 4 spawning migrations. Furthermore, in the Nass watershed, different life-histories were differently prevalent through time-three different life-histories were the most prevalent in a given year and no life-history ever represented more than 45% of the population. These asynchronous dynamics among life-histories decreased the variability of numerical abundance and biomass of the aggregated population so that it was more than 20% more stable than the stability of the weighted average of specific life-histories, evidence of a substantial portfolio effect. Year of ocean entry was a key driver of dynamics; the median correlation coefficient of abundance of life-histories that entered the ocean the same year was 2.5 times higher than the median pairwise coefficient of life-histories that entered the ocean at different times. Simulations illustrated how different elements of life-history diversity contribute to stability and persistence of populations. 4.This study provides evidence that life-history diversity can dampen fluctuations in population abundances and biomass via portfolio effects. Conserving genetic integrity and habitat diversity in this and other large watersheds can enable a diversity of life-histories that increases stability to environmental variability. This article is protected by copyright. All rights reserved.
In Washington State, the approach to management of wild and hatchery steelhead trout Oncorhynchus mykiss has been to separate the timing of return and spawning by the two groups through selective breeding for early timing in hatchery fish. However, overlap in timing and spatial distribution could permit genetic and ecological interactions. To evaluate this man- agement approach, we compared the timing, spatial distribution, and size of adult steelhead in the wild and newly established hatchery populations of Forks Creek, Washington. Hatchery fish tended to return and spawn about 3 months before wild fish but there was some temporal overlap. Radio- tracking indicated that the spatial distributions of the populations overlapped considerably, per- mitting interbreeding and ecological interactions. However, the hatchery fish tended to stay closer to the hatchery, consistent with olfactory imprinting on the hatchery's water supply. Wild females were larger than hatchery females (median fork lengths were 670 and 644 mm, respectively), and wild males and females varied more in length than did hatchery fish of the same sex. In the first year in which naturally spawned offspring of hatchery fish might have returned, we observed a marked increase in early-returning unmarked (i.e., naturally spawned) adults, suggesting that some hatchery fish spawned successfully in the creek.
We investigated the distribution and predation activities of northern Squawfish Ptychocheilus oregonensis at three locations where hatchery-reared juvenile salmonids Oncorhynchus spp. were released in Bonneville Pool, a Columbia River reservoir. Significant increases in northern Squawfish catch rate occurred at all three locations after releases. The timing and duration of elevated catch rates appear to be closely related to the release and subsequent residence time of the hatchery-released fish in the sampling area. Northern Squawfish caught after salmonid releases had a significantly higher frequency of occurrence and mean number of juvenile salmonids in their diet compared with fish caught before releases. Consumption indices, relative measures of consumption rates, were also higher at each location after release, Our results suggest that northern Squawfish aggregate to feed on hatchery-released juvenile salmonids in the spring. Management activities to reduce predation on juvenile salmonids should consider (1) removing predators from areas where they concentrate to feed on juvenile salmonids, specifically near hatchery release points where the residence time of juveniles may be prolonged, (2) releasing hatchery fish that are larger, and (3) adopting hatchery release plans that reduce the residence time of hatchery fish at the release location.
Steelhead Onchorhynchus mykiss exhibit a wide range of life histories within and among stocks. Varying degrees of anadromy, length of freshwater life before emigration to the sea, and age at first maturity have been observed. Steelhead in the mid-Columbia River basin are at least partially descended from fish that were relocated to the major tributaries of the mid-Columbia River when Grand Coulee Dam was built. These fish do not spawn in the main-stem Columbia River and are strictly tributary spawners. Rearing conditions in these tributaries can be harsh. Researchers have observed a wide range of lengths and ages of juvenile O. mykiss (steelhead and nonanadromous rainbow trout) in these tributaries. This led to a need to document the age at migration of fish that were clearly smolts, as demonstrated by their downstream migration. Over 970 otoliths were collected from naturally produced steelhead smolts in 1988 and 1989 to determine the age at migration. Ages ranged from 1 to 7 years at Rock Island Dam and from 1 to 5 years at Rocky Reach Dam. These ages agreed with those estimated from adult otoliths. Age structure did not differ significantly between the two sampling sites, but length did, suggesting that fish emigrating from the Wenatchee River were shorter for a given age than fish produced above Rocky Reach Dam. Females made up 63.0% of the smolts collected at Rock Island Dam and were generally older than males, suggesting that males have a higher probability of remaining in freshwater. We attempt to explain the patterns observed in age and length of naturally produced steelhead smolts. We suggest that a more or less continuous downstream movement of juveniles occurs that takes them to areas with more adequate food supplies. Smoltification of individual fish appears to result as a threshold length is approached. Harsher growing conditions result in slower growth and older smolts, which may have implications for supplementation and introduction of steelhead where resident rainbow trout are present.
Hatchery and wild fish advocates often engage in lively debates about the ecological interactions between hatchery and wild fish. Many arguments about ecological interactions between hatchery and wild fish have been fueled by a variety of misconceptions, scientific uncertainties, and differences of unstated objectives. In order to reduce the frequency of unfruitful discussions, it is important to expose a variety of misconceptions and scientific uncertainties about ecological interactions and risk. In addition, it is necessary to synthesize what is currently known about ecological interactions. Seven misconceptions, three realities, and four of the most important scientific uncertainties are described. I conclude that ecological interactions between hatchery and wild fish will occur but whether those interactions are biologically significant, socially acceptable, and whether any impacts are statistically detectable are probably dependant upon the characteristics of the hatchery program, naturally-produced fish, natural environment where hatchery fish are released, and how interactions are evaluated. Large-scale experiments will be necessary to resolve existing scientific uncertainty, but in the mean time, risk assessments, weight-of-evidence and precautionary approaches, and separating technical and policy discussions can be used to improve evaluation and management of ecological interactions between hatchery and wild fish.
The practical difficulties in measuring the prevalence, incidence, and pathogenicity of diseases in wild Atlantic salmon populations cause serious problems in determining the possible implications of disease. Limited research has been undertaken on wild salmon disease associated with environmental effects of fish farming, or with the disease implications of possible changes to the genetic make-up of wild salmonid stocks as a consequence of farmed fish escaping. To date, no significant disease problems have been reported linked to these aspects. The greatest disease risk to both farmed and wild stocks is through the introduction of exotic pathogens into areas where local stocks have no innate resistance. National and international legislative controls are in existence to reduce this risk, but these have not afforded total protection. Serious epizootics of furunculosis and Gyrodacfylus saluris in stocks of salmon indicate the severe consequences of new disease outbreaks linked to movements of live fish for farming or restocking purposes. A wide mnge of infectious agents has been recorded from wild salmon and some of these (and from other species of wild fish) provide the primary source of infection leading to disease problems in fish farms. Although disease control has markedly improved in fish farms in recent years, problems still remain with some diseases, notably sea lice. It is likely that the lice population and other diseases in farms contribute infection to local wild stocks, but the extent and consequences of this have not been quantified. 0 British Crown copyright 1997
We conducted a literature review on predation by hatchery yearling salmonids on wild subyearling salmonids in the western
United States. The review included 14 studies from the Pacific Northwest and California. In most instances, predation by hatchery
yearling salmonids on wild subyearling salmonids occurred at low levels. However, when multiple factors contributing to the
incidence of predation were met, localized areas of heavy predation were noted. Total prey consumed ranged from 456 to 111
000 subyearlings for the few studies in which enough information was gathered to make the estimate. We examined two of these
studies in more detail: one detecting relatively low predation in four western Washington rivers and one detecting relatively
high predation in the Trinity River in northern California. In the case of the rivers in western Washington, over 70% of wild
subyearlings had migrated by the time hatchery steelhead were planted and those remaining had grown large enough to reduce
their vulnerability to predation. In the case of the Trinity River, less than 20% of wild subyearlings had migrated by the
time hatchery steelhead were planted and most were small enough to remain highly vulnerable to predation. We found that managers
can effectively minimize the predation rate of hatchery yearling salmonids by reducing the spatial or temporal overlap of
predator and prey. Unknown is the extent to which low predation rates, which likely occur in most places hatchery yearlings
are released, might still negatively impact prey populations that are at low abundance because of other anthropogenic factors.
In 2004 and 2005, steelhead (anadromous rainbow trout Oncorhynchus mykiss) reared at Winthrop National Fish Hatchery (Winthrop, Washington) were tagged with passive integrated transponders and subjected to a volitional or forced release. Gill Na, K-ATPase (NKA) activity, body size, condition factor (K), travel time, and apparent survival were compared between volitional migrants (VMs), forced-release migrants (FRMs), and volitional-release nonmigrants (VNMs). Gill NKA activity and body size were similar between VNM, VM, and FRM groups, but K varied by date and migrant group. However, by the end of the volitional-release period, all three groups had similar K. The VNMs consistently demonstrated lower apparent survival to McNary Dam on the Columbia River than did the VM and FRM groups, which had three to eight times greater survival than did VNMs. Volitional migrants had higher apparent survival to McNary Dam than did FRMs in 2005; however, apparent survival was similar between the two groups in 2004. Apparent survival between McNary and John Day dams was similar among all three groups in 2004 and 2005. Median travel time to McNary Dam was not consistently different among groups and differed between years. By combining results from VNMs and VMs, we were able to compare apparent survival between volitional- and forced-release strategies. In 2004, the forced-release group had a significantly higher apparent survival to McNary Dam than did volitionally released fish, whereas there was no difference in apparent survival between the two release strategies in 2005. There was little evidence for a survival-, size-, or physiology-related advantage of volitionally released fish over forced-release fish. The consistently lower apparent survival of VNMs does support the use of volitional release to screen fish that will fail to migrate downstream due either to low survival or residualization in the natal stream.
We developed and tested a release strategy designed to reduce the number of hatchery-reared steelhead Oncorhynchus mykiss that fail to migrate out of the Tucannon River (i.e., residualize) in southeast Washington. We also described the physical characteristics of those fish that failed to emigrate. Hatchery-reared steelhead that residualize may have negative effects on naturally produced salmonids through competition for food and space, predation, and the spread of disease. Steelhead residualism was reduced by retaining fish in the Curl Lake acclimation pond after volitional emigration had ceased. Fish that remained in the pond had a male : female ratio of 4: 1; 90% of these fish were a combination of transitional, parr, and precocious male stages. This method resulted in 2,022 residualized fish in the Tucannon River, 3.l% of the fish planted in Curl Lake. During the same year, 4,186 fish (14.0% of fish released) residualized in the Tucannon River from a direct river release. The 3.1 % residualism of the fish planted in Curl Lake in 1993 was significantly lower than the 14.0% residualism that occurred in 1993 from the direct river release and the 17.7% and 10.3% percent residualism for fish planted into Curl Lake in 1991 and 1992. By retaining 13,971 probable residual fish in Curl Lake in 1993, potential negative interactions in the natural river environment were substantially reduced. Fish remaining in Curl Lake were harvested by sport anglers after June 1, 1993, when the lake opened for sport fishing.
To aid in the recovery of depressed wild salmon populations, the operation of hatcheries must be changed to reduce interactions of juvenile hatchery fish with wild fish. Evidence suggests that productivity of wild populations can be reduced by the presence of large numbers of hatchery smolts in lower rivers and estuaries that attract predators. An index of productivity based on the density-independent rate of reproduction of wild coho salmon (Oncorhynchus kisutch) in 12 Oregon coastal river basins and two lake basins was negatively correlated with the average number of hatchery coho salmon smolts released in each basin. The index of productivity was not significantly correlated with the average proportion of hatchery coho salmon in each naturally spawning population or with habitat quality. Alterations to hatchery programs that could encourage recovery of wild populations include (i) avoiding release of large numbers of smolts in areas with high concentrations of wild fish, (ii) decreasing the number of smolts released, and (iii) using a volitional release strategy or a strategy that employs smaller release groups spread temporally.
The incidence of precocious steelhead trout (Salmo gairdneri) was determined in several Idaho hatchery steelhead populations. The range of incidence of precocious males was 0–64% of the sampled populations. This variation appeared to be related to age of the trout, water temperature, and photoperiod. The incidence of precocious males greatly exceeded the incidence (0.1% of the population when encountered) of precocious females. Precocious male steelhead trout are apparently lost from the migrating smolt population and display mating behavior similar to sea-run adult male steelhead. Precocious males maintained in laboratory conditions remained sexually mature for at least 6 mo of observation. This was reflected by mean gonadal weights and mean gonadosomatic indices from precocious male steelhead which differed significantly from nonprecocious juvenile male steelhead maintained under similar conditions. No consistent pattern of growth was observed among laboratory-maintained trout. Key words: steelhead trout, reproduction, precocious sexual maturation, age, photoperiod, temperature
In male Chinook Salmon Oncorhynchus tshawytscha, age of maturation is phenotypically plastic, occurring at age 1 (referred to as precocious parr or microjack), age 2 (minijack), age 3 (jack), age 4, or age 5. Microjacks and minijacks are thought to forego migration to the ocean as smolts, instead remaining in headwaters and employing a “sneaking” strategy to fertilize eggs. We compared the prevalence of minijacks (minijack rate) among hatchery- and natural-origin spring Chinook Salmon from the Yakima River, Washington, over seven brood years (2001–2007). We quantified minijack rates and sex ratios in the hatchery population prior to release and during out-migration at a trap located 230 km downstream. Within this time period, we also monitored minijack rates in a 3-year (brood years 2002–2004) growth study designed to reduce minijack production at the hatchery. Minijacks made up an average of 41% of the male population in the hatchery, but annual minijack rates varied in response to the growth rate or fish size at release. Average minijack rate was approximately 20% among out-migrating hatchery fish, about half the rate found prior to release. Among out-migrants, minijack rates of hatchery fish were approximately 10 times those of natural-origin fish, but sex ratios were significantly skewed toward females in both hatchery- and natural-origin groups. Data from this study and related studies suggest that the predominant age of early male maturation in the Yakima River and similar rivers is age 2 (minijack) in hatchery fish and age 1 (microjack) in natural-origin fish. Based on this and other studies, we now recognize three minijack life history types in spring Chinook Salmon: resident, fluvial, and anadromous, depending on the migration pattern exhibited in the spring and summer. Finally, we discuss the broader impacts that high minijack production may have on the establishment of size-at-release targets for salmon supplementation programs in the future.Received July 11, 2012; accepted November 13, 2012
Freshwater residualization, whereby anadromous juvenile salmonids fail to emigrate seawards within the primary migration period, causes considerable economic and ecological management concern. Previous studies have attempted to identify possible factors contributing to residualization, including both fish-related and release methodology-related attributes, in order to develop measures to reduce it. Here, we synthesize 48 previous estimates of the residualization rates of hatchery-reared steelhead Oncorhynchus mykiss from 16 studies and evaluate the cross-study effects of several factors that can be controlled by hatchery managers. The proportion of fish in hatchery release groups that residualized ranged from 0% to 17% (average, 5.6%). Characteristics of the release process were dominant in affecting residualization rates, while characteristics of individual steelhead primarily determined which, but not how many, individuals residualized. Releases of fewer fish and those located closer to the ocean or to a confluence with a major river produced fewer residuals than larger releases located further upstream. Acclimation ponds also appeared to reduce residualization, but there was no evidence of a release date effect across locations and years. Within a release year, individuals from endemic broodstock had higher residualization rates than those from hatchery-propagated broodstock while smaller individuals and larger males were more likely to residualize than individuals of intermediate size (similar to 213 mm fork length). To meet management objectives of reducing steelhead residualization, we recommend releases closer to an ocean or large river, particularly for releases of relatively few fish, in conjunction with the use of acclimation ponds. Management effort should focus on selective harvesting of hatchery residuals, a process which may be supported by rearing and release strategies. These objectives may trade off with conservation objectives; straying risk and genetic effects should especially be taken into account.
At two Washington State hatcheries in August 1999–2002, juvenile steelhead Oncorhynchus mykiss were size-graded and the largest fish (4.8–9.2% of the population) were coded-wire-tagged and mixed with small fish to determine whether the large fish were those that became precocious males. The results showed that the large fish in August at Merwin Hatchery tended to become precocious, although the mean lengths of the precocious and nonprecocious fish were similar at their time of release in April. At Abernathy Fish Technology Center (FTC), the large fish in August did not disproportionately become precocious, and the nonprecocious fish were significantly larger than the precocious fish at release. We suggest that precocious fish at Abernathy FTC may have committed to precocity before August whereas fish at Merwin Hatchery committed to precocity in August. Because only 0.82% of the large fish became precocious, removing the 5–10% largest fish in August at the Merwin Hatchery would be marginally successful in reducing the number of precocious males.
Residualism is the failure of some hatchery-reared salmonid juveniles to out-migrate as smolts with the rest of their cohort. We released hatchery-reared juveniles from domesticated- and wild-origin broodstock steelhead and measured their relative rates of residualism. The residualism rate exhibited by the offspring of wild broodstock was more than one order of magnitude greater than that of domesticated stock. Further, we experimentally manipulated the growth trajectories of juvenile offspring of wild broodstock to decrease the size variance among released fish. Our expectation was that fewer fish would be too small or too large to smolt as yearlings. Small fish placed on an aggressive rearing regimen (reared separately from larger fish, fed more food more often) residualized at a lower rate than did comparable control fish (reared with large fish without supplemental feeding). We saw no effect of a lower feeding regimen on the residualism rate of large fish, but the lower feeding regimen did not significantly affect size during rearing. Residual steelhead were bimodally distributed by size. Most residual fish were male; among these fish, 11-ketotestosterone levels and visual scores of gonadal development indicated that 42% were mature or maturing. All fish showed the expected patterns of change in gill Na,K-ATPase and insulin-like growth factor-I (IGF-I) associated with smoltification, and small fish placed on the aggressive rearing regimen showed slightly, but significantly, higher IGF-I levels than did comparable control fish.
Fish lengths have been measured in many different ways. The differences arise from choosing different reference points near the anterior end and near the posterior end of the fish, and from using different methods of making the measurement. Methods of making the measurement include using calipers; using a tape held along the curve of the body; laying the fish on a measuring board with the front end pressed against an upright piece; laying the fish on a board with a movable cross hair above it, attached to an indicator running along a scale. In theory, any combination of reference points and methods might be used, but practice is considerably more restricted. Some of the commoner combinations have special names; these are provided in the chapter, together with the reference points used. In addition to these methodological differences, length varies with the condition of the fish—for example, whether it is alive, recently killed, after rigor mortis has set in, or at different intervals of time after preservation in formalin or alcohol.
Backcalculated lengths at the end of the first growth season in wild Atlantic salmon Salmo salar differed significantly between parr smolting at age 1, 2 and 3 years over a period of 11 years (i.e. 1983–1993). Mean body lengths of the respective age groups at the end of the first growth period were 11·1, 6·2 and 4·7 cm, respectively. The mean percentage distribution of fish smolting at age 1, 2 and 3 was 14, 78 and 7%, and the mean smolt age was 1·95 years. Mean lengths at smolting of age groups 1, 2 and 3 were 13·6, 15·8 and 17·5 cm, respectively. Females outnumbered males among the downstream migrating smolts with a mean sex ratio (females/ males) estimated at 1·61, with a significant female surplus in 7 of the 11 years sampled. Of the smolts sampled, 14% exhibited enlarged gonads indicative of parr maturation, and all were males (37% of the parr males sampled). Mean annual smolt density from 1975 to 1996 was 13·4 individuals 100 m−2 ranging between 0·3–31 smolts 100 m−2. Mean densities (100 m−2) of the smolts aged 1, 2 and 3 years were 1·5, 9·3 and 0·9 fish, respectively. Mean annual biomass for the 22-year period (1975–1996) was estimated at 437 g 100 m−2, with a range of variation from 136 to 683 g 100 m−2. Smolt age 2 made up 81% of the mean annual biomass (355 g 100 m−2) and smolt age 1 and 3, 8% (35 g 100 m−2) and 11% (47 g 100 m−2), respectively.
Hatcheries have been built and operated to buffer salmon and trout populations from overfishing and to compensate for habitat lost or degraded by human activities. These facilities are now so prevalent that in some cases hatchery-produced salmon outnumber salmon produced in the wild. By default, this makes them an important component in the current ecology and evolution of salmonids. Hatcheries differ from natural environments in many ways, and among the most fundamental is the necessity that humans select fish for breeding instead of allowing natural processes of mate choice and competition. We examined the mating system for steelhead trout (Oncorhynchus mykiss) at Forks Creek Hatchery in southwest Washington and investigated factors affecting selection of individual steelhead for spawning by the hatchery staff. Despite efforts by the staff to not spawn selectively, data on steelhead spawned over 7 years revealed selection for large adult body size and early reproductive timing and a tendency for size-assortative mating (i.e., large with large). Selection on size was related to selection on reproductive timing because early returning fish tended to be larger than those returning later. To improve the fitness of both hatchery fish destined to spawn in the wild and hatchery fish designated to be spawned in the hatchery, a better understanding of factors associated with the range of reproductive success and mate-choice mechanisms in the wild is vital. This knowledge may then be applied to artificial propagation programs designed for conservation or enhancement.