Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet,Southeast Alaska

Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska. In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks.     

Evidence for competition at sea between Norton Sound chum salmon and Asian hatchery chum salmon

Increasing production of hatchery salmon over the past four decades has led to concerns about possible density-dependent effects on wild Pacific salmon populations in the North Pacific Ocean. The concern arises because salmon from distant regions overlap in the ocean, and wild salmon populations having low productivity may compete for food with abundant hatchery populations. We tested the hypothesis that adult length-at-age, age-at-maturation, productivity, and abundance of a Norton Sound, Alaska, chum salmon population were influenced by Asian hatchery chum salmon, which have become exceptionally abundant and surpassed the abundance of wild chum salmon in the North Pacific beginning in the early 1980s. We found that smaller adult length-at-age, delayed age-at-maturation, and reduced productivity and abundance of the Norton Sound salmon population were associated with greater production of Asian hatchery chum salmon since 1965. Modeling of the density-dependent relationship, while controlling for other influential variables, indicated that an increase in adult hatchery chum salmon abundance from 10 million to 80 million adult fish led to a 72% reduction in the abundance of the wild chum salmon population. These findings indicate that competition with hatchery chum salmon contributed to the low productivity and abundance of Norton Sound chum salmon, which includes several stocks that are classified as Stocks of Concern by the State of Alaska. This study provides new evidence indicating that large-scale hatchery production may influence body size, age-at-maturation, productivity and abundance of a distant wild salmon population.     

Straying of hatchery salmon in Prince William Sound,Alaska

The straying of hatchery salmon may harm wild salmon populations through a variety of ecological and genetic mechanisms. Surveys of pink (Oncorhynchus gorbuscha), chum (O. keta) and sockeye (O. nerka) salmon in wild salmon spawning locations in Prince William Sound (PWS), Alaska since 1997 show a wide range of hatchery straying. The analysis of thermally marked otoliths collected from carcasses indicate that 0–98% of pink salmon, 0–63% of chum salmon and 0–93% of sockeye salmon in spawning areas are hatchery fish, producing an unknown number of hatchery-wild hybrids. Most spawning locations sampled (77%) had hatchery pink salmon from three or more hatcheries, and 51% had annual escapements consisting of more than 10% hatchery pink salmon during at least one of the years surveyed. An exponential decay model of the percentage of hatchery pink salmon strays with distance from hatcheries indicated that streams throughout PWS contain more than 10% hatchery pink salmon. The prevalence of hatchery pink salmon strays in streams increased throughout the spawning season, while the prevalence of hatchery chum salmon decreased. The level of hatchery salmon strays in many areas of PWS are beyond all proposed thresholds (2–10%), which confounds wild salmon escapement goals and may harm the productivity, genetic diversity and fitness of wild salmon in this region     

Some consequences of Pacific salmon hatchery production in Kamchatka: changes in age structure and contributions to natural spawning populations

Aggregate hatchery production of Pacific salmon in the Kamchatka region of the Russian Federation is very low (< 0.5% of total harvest, with five hatcheries releasing approximately 41 M juvenile salmon annually), but contributions in certain rivers can be substantial. Enhancement programs in these rivers may strongly influence fitness and production of wild salmon. In this paper we document significant divergence in demographic traits in hatchery salmon populations in the Bolshaya River and we estimate the proportion of hatchery chum salmon in the total run in the Paratunka River to demonstrate the magnitude of enhancement in this system. We observed a reduction in the expression of life history types in hatchery populations (ranging from 1 to 9 types) compared to wild populations (17 types) of sockeye salmon in the Bolshaya River. We found similar trends in Chinook salmon in the same river system. This reduced life history diversity may make these fish less resilient to changes in habitat and climate. We estimate hatchery chum salmon currently contribute 17-45% to the natural spawning population in the Paratunka River. As hatchery fish increase in numbers at natural spawning sites, this hatchery production may affect wild salmon production. It is important to investigate the risk of introgression between hatchery and wild salmon that can lead to reduction in salmon fitness in Kamchatka rivers, as well as the potential of ecological interactions that can have consequences on status of wild salmon and overall salmon production in this region.     

An overview of salmon enhancement and the need to manage and monitor natural spawning in Hokkaido, Japan

The chum and pink salmon catches in Hokkaido, Japan have increased dramatically since the 1970s and the 1990s, respectively. In contrast, masu salmon catches have been steadily decreasing. Despite intensive hatchery development in Hokkaido, naturally spawning salmon populations persist based on results from a recent river survey. This paper focuses on the challenges of maintaining hatchery salmon populations while protecting natural chum, pink and masu salmon populations in Hokkaido. Two important initiatives related to meeting this ambitious goal are managing hatcheries in a way that minimizes negative interactions between natural and hatchery salmon populations, and initiating new efforts at restoring and rehabilitating degraded freshwater habitats. In addition, in order to maintain a balance of demand and supply in the domestic market through the exportation of extra salmon, Hokkaido has decided to enter full assessment to gain Marine Stewardship Council (MSC) certification of the Hokkaido chum salmon trap net fishery. This would involve a fundamental shift in fisheries management as practiced in Japan, specifically elevating the importance of managing the fishery in a way that conserves natural salmon populations. A key component of a new salmon management strategy is the establishment of a zone management framework based on the designation of stream units to spatially separate natural salmon from hatchery salmon to minimize negative effects of hatchery fish and to utilize effectively hatchery salmon for commercial fisheries. This effort is allied with similar initiatives in other Pacific Rim countries that are focusing on management reform to restore natural ecosystem function and maintain the coexistence of wild and hatchery salmon.     

Migration of Pacific Rim Chum Salmon on the High Seas: Insights from Genetic Data

Wild stocks of chum salmon, Oncorhynchus keta, have experienced recent declines in some areas of their range. Also, the release of hatchery chum salmon has escalated to nearly three billion fish annually. The decline of wild stocks and the unknown effects of hatchery fish combined with the uncertainty of future production caused by global climate change have renewed interest in the migratory patterns of chum salmon on the high seas. We studied the composition of high-seas mixtures of maturing and immature individuals using baseline data for 20 allozyme loci from 356 populations from throughout the Pacific Rim. Composition estimates were made from three time series. Two of these time series were from important coastal migratory corridors: the Shumagin Islands south of the Alaska Peninsula and the east coast of the Kamchatka Peninsula. The third was from chum salmon captured incidentally in the Bering Sea trawl fishery for walleye pollock. We also analyzed geographically dispersed collections of chum salmon captured in the month of July. The time series show dynamic changes in stock composition. The Shumagin Island corridor was used primarily by Northwest Alaskan and Asian populations in June; by the end of July stocks from the Alaska Peninsula and southern North America dominated the composition. The composition along the Kamchatka coast changed dramatically from primarily Russian stocks in May to primarily Japanese stocks in August; the previously undocumented presence of stocks from the Alaska Peninsula and Gulf of Alaska was also demonstrated. Immature chum salmon from throughout the Pacific Rim, including large proportions of southern North American stocks, contributed to the Bering Sea bycatch during the months of September and October. The migration routes of North American stocks is far more widespread than previously observed, and the Bering Sea is an important rearing area for maturing and immature chum salmon from throughout the species' range.     

Differential Reproductive Success of Sympatric, Naturally Spawning Hatchery and Wild Steelhead, Oncorhynchus mykiss

Hatchery propagation of salmonids has been practiced in western North America for over a century. However, recent declines in wild salmon abundance and efforts to mitigate these declines through hatcheries have greatly increased the relative abundance of fish produced in hatcheries. The over-harvest of wild salmon by fishing mixed hatchery and wild stocks has been of concern for many years but genetic interactions between populations, such as hybridization, introgression and outbreeding depression, may also compromise the sustainability of wild populations. Our goal was to examine whether a newly established hatchery population of steelhead trout successfully reproduced in the wild and to compare their rate of reproductive success to that of sympatrically spawning native steelhead. We used eight microsatellite loci to create allele frequency profiles for baseline hatchery and wild populations and assigned the smolt (age 2) offspring of this parental generation to a population of origin. Adults originating from a generalized hatchery stock artificially selected for early return and spawning date were successful at reproducing in Forks Creek, Washington. Although hatchery females (N = 90 and 73 in the two consecutive years of the study) produced offspring that survived to emigrate as smolts, they produced only 4.4–7.0% the number produced per wild female (N = 11 and 10). This deficit in reproductive success implies that the proportion of hatchery genes in the mixed population may diminish since deliberate releases into the river have ceased. This hypothesis is being tested in a long-term study at Forks Creek.     

Wild and hatchery reproduction of pink and chum salmon and their catches in the Sakhalin-Kuril region,Russia

In the Sakhalin-Kuril region hatchery culture of pink and chum salmon is of great importance compared to other regions of the Russian Far East. During the last 30 years the number of hatcheries increased two-fold, and significant advances were made in hatchery technologies. As a result, chum salmon capture in regions where hatcheries operate (southwestern and eastern Sakhalin coasts, and Iturup Island) was 9 times as high during 2006–2010 than during 1986–1990, whereas wild chum salmon harvest markedly declined. Recent dynamics in pink salmon catch appear to track trends in natural spawning in monitored index rivers, suggesting natural-origin pink salmon play a dominant role in supporting the commercial fishery. It remains uncertain as to whether hatcheries have substantially supplemented commercial catch of pink salmon in this region, and I recommend continued research (including implementing mass marking and recovery programs) before decisions are made regarding increasing pink salmon hatchery production. Location of hatcheries in spawning river basins poses problems for structuring a management system that treats hatchery and wild populations separately. Debate continues regarding the existence and importance of density-dependent processes operating in the ocean environment and the role hatcheries play in these processes. Loss of critical spawning habitat for chum salmon in the Sakhalin-Kuril region has lead to significant declines in their abundance. I conclude by recommending increases in releases of hatchery chum salmon numbers in the region to help recover depressed wild populations and provide greater commercial fishing benefits in the region.     

Comparison of maturation timing,egg size and fecundity between hatchery lines of chinook salmon and their wild donor stocks

Increasing concern has been expressed about the genetic effects of cultured salmonid fishes on natural populations. Avoidance of extreme negative outcomes was one reason for the establishment of a genetic management policy for the State of Alaska. However, domestication within the hatchery may still cause divergence from the wild donor population. This divergence could potentially lead to adverse impacts on wild stocks through straying and introgression. This study examines potential domestication in two Alaskan chinook salmon stocks. The Little Port Walter (LPW) Hatchery Chickamin River stock resulted from a small collection of wild broodstock in 1976. The LPW Unuk stock was founded with a larger number of individuals in 1976 and has had subsequent infusion of wild gametes. These lines have been maintained at LPW through ocean ranching of tagged smolts. Comparisons are made between the hatchery lines, progeny of wild chinook collected from the Chickamin and Unuk Rivers, and hybrids between the hatchery and wild groups. Mature ocean‐ranched female chinook salmon returning to the facility were periodically graded for ripeness and spawned. Body size and meristic measurements were collected from these mature spawners. Maturation timing, fecundity, and individual egg size of these fourth generation hatchery fish are compared with that of offspring of wild fish from the same donor stock. Stock of origin is confirmed for all spawners and offspring using microsatellite DNA analysis.     

Consequences to fitness‐related traits of hybridization between farmed and wild Atlantic salmon, Salmo salar

Increasing concern has been expressed about the genetic effects of cultured salmonid fishes on natural populations. Avoidance of extreme negative outcomes was one reason for the establishment of a genetic management policy for the State of Alaska. However, domestication within the hatchery may still cause divergence from the wild donor population. This divergence could potentially lead to adverse impacts on wild stocks through straying and introgression. This study examines potential domestication in two Alaskan chinook salmon stocks. The Little Port Walter (LPW) Hatchery Chickamin River stock resulted from a small collection of wild broodstock in 1976. The LPW Unuk stock was founded with a larger number of individuals in 1976 and has had subsequent infusion of wild gametes. These lines have been maintained at LPW through ocean ranching of tagged smolts. Comparisons are made between the hatchery lines, progeny of wild chinook collected from the Chickamin and Unuk Rivers, and hybrids between the hatchery and wild groups. Mature ocean‐ranched female chinook salmon returning to the facility were periodically graded for ripeness and spawned. Body size and meristic measurements were collected from these mature spawners. Maturation timing, fecundity, and individual egg size of these fourth generation hatchery fish are compared with that of offspring of wild fish from the same donor stock. Stock of origin is confirmed for all spawners and offspring using microsatellite DNA analysis.     

Effect of hatchery environment on cranial morphology and developmental stability of Atlantic salmon (Salmo salar L.) from North‐West Russia

The study addresses the effect of hatchery rearing on morphological variation and developmental stability of Atlantic salmon parr from North‐West Russia. Totally, we collected nine samples. Four wild samples were collected from each of the rivers Kola, Umba, Keret’ and Shuia. Five samples of hatchery‐reared parr were the first‐generation progeny of wild adults from these rivers reared separately at the four hatcheries (one hatchery was represented by two samples). Ten meristic and 48 morphometric cranial characters were analysed. We studied the morphological divergence between wild and hatchery fishes of the same river of origin. To analyze developmental stability we used fluctuating asymmetry (random deviations from perfect bilateral symmetry). It was found that hatchery‐reared parr significantly differ from wild parr in both meristic characters and the shape of cranial bones. Different hatcheries caused similar effect on morphological variation in all populations. Fluctuating asymmetry in morphometric characters was significantly higher in hatchery fish than in wild from the Shuia River, indicating a higher level of developmental instability. However, wild parr from the Keret’ River had significantly higher fluctuating asymmetry than cultivated parr of the same origin, possible due to a high infection pressure of the parasite Gyrodactylus salaris Malmberg which has led to significant decline of the wild salmon population in this river, or from genetic changes caused by cultivation. The obtained results indicate a notable effect of hatchery environment on Atlantic salmon’s phenotype.     

Compensatory releases reduce genetic differentiation among Atlantic salmon populations in the Baltic Sea: evidence from the River Ume‐Vindelälven

About 90% of salmon smolts in the Baltic Sea derive from hatchery enhancement programmes designed to compensate for loss of catches and genetic resources due to the damming of salmon rivers. The potential threat of genetic homogenization from extensive hatchery releases, however, has not been thoroughly investigated. We provide evidence that straying from deliberate releases poses a threat to indigenous populations by identifying the origin of 127 fin‐clipped (hatchery) salmon caught in the River Ume‐Vindelälven during 1997 to 2000, using mtDNA and six microsatellite loci. The analysis of eight potential donor stocks revealed that compensatory releases from the R. Ångerman and R. Luleälven hatcheries have resulted in a significant amount of straying to the river Ume‐Vindelälven (at least 10 and 12 migrants per year). As predicted to due to increased migration, the analysis of temporal samples from the wild population of R. Vindelälven showed a decreasing trend in genetic differentiation estimates (measured as Fst) relative to hatchery the hatchery strains of R. Ångermanälven and R. Luleälven. Our results suggest that gene flow from compensatory releases poses a serious threat to the genetic makeup of the existing wild populations in the Baltic.     

Extensive immigration from compensatory hatchery releases into wild Atlantic salmon population in the Baltic sea: spatio-temporal analysis over 18 years

Genetic homogenization has been recognized as a serious threat in an increasing number of species, including many salmonid fishes. We assessed the rate and impact of immigration from the main hatchery stocks of Atlantic salmon in the Gulf of Bothnia into one of the largest wild salmon populations in the Baltic Sea, the River Vindel?lven, within a temporal framework of 18 years (from 1985-2003). We provide genetic evidence based on mtDNA and microsatellite markers, using mixed-stock analysis, that a large proportion (66%) of fin-damaged spawners (n=181) caught in the Ume/Vindel?lven during 1997-2003 originated from the hatcheries in the Rivers Angerman?lven, Lule?lven and Ljusnan. The maximum-likelihood estimate of immigration rate from these hatcheries into the wild Vindel?lven population was 0.068 (95% CI 0.021-0.128) over the studied time period (1985-2003) and reached up to a quarter (m=0.249, 95% CI 0.106-0.419) of the total population during 1993-2000. This resulted in significant (P<0.01) genetic homogenization trend between the wild Vindel?lven population and hatchery stocks of the Angerman?lven and Lule?lven. Our results demonstrate extensive straying from geographically distant hatchery releases into wild salmon population and emphasize the genetic risks associated with current large-scale stocking practices in the Baltic Sea.     

Variation in migration pattern,broodstock origin,and family productivity of coho salmon hatchery populations in British Columbia,Canada, derived from parentage‐based tagging

In salmonid parentage‐based tagging (PBT) applications, entire hatchery broodstocks are genotyped, and subsequently, progeny can be nonlethally sampled and assigned back to their parents using parentage analysis, thus identifying their hatchery of origin and brood year (i.e., age). Inter‐ and intrapopulation variability in migration patterns, life history traits, and fishery contributions can be determined from PBT analysis of samples derived from both fisheries and escapements (portion of a salmon population that does not get caught in fisheries and returns to its natal river to spawn). In the current study of southern British Columbia coho salmon (Oncorhynchus kisutch) populations, PBT analysis provided novel information on intrapopulation heterogeneity among males in the total number of progeny identified in fisheries and escapements, the proportion of progeny sampled from fisheries versus escapement, the proportion of two‐year‐old progeny (jacks) produced, and the within‐season return time of progeny. Fishery recoveries of coho salmon revealed heterogeneity in migration patterns among and within populations, with recoveries from north and central coast fisheries distinguishing “northern migrating” from “resident” populations. In northern migrating populations, the mean distance between fishery captures of sibs (brothers and sisters) was significantly less than the mean distance between nonsibs, indicating the possible presence of intrapopulation genetic heterogeneity for migration pattern. Variation among populations in productivity and within populations in fish catchability indicated that population selection and broodstock management can be implemented to optimize harvest benefits from hatcheries. Application of PBT provided valuable information for assessment and management of hatchery‐origin coho salmon in British Columbia.     

Changes in Size and Age of Chinook Salmon Oncorhynchus tshawytscha Returning to Alaska

The average sizes of Pacific salmon have declined in some areas in the Northeast Pacific over the past few decades, but the extent and geographic distribution of these declines in Alaska is uncertain. Here, we used regression analyses to quantify decadal trends in length and age at maturity in ten datasets from commercial harvests, weirs, and spawner abundance surveys of Chinook salmon Oncorhynchus tshawytscha throughout Alaska. We found that on average these fish have become smaller over the past 30 years (~6 generations), because of a decline in the predominant age at maturity and because of a decrease in age-specific length. The proportion of older and larger 4-ocean age fish in the population declined significantly (P < 0.05) in all stocks examined by return year or brood year. Our analyses also indicated that the age-specific lengths of 4-ocean fish (9 of 10 stocks) and of 3-ocean fish (5 of 10 stocks) have declined significantly (P < 0.05). Size-selective harvest may be driving earlier maturation and declines in size, but the evidence is not conclusive, and additional factors, such as ocean conditions or competitive interactions with other species of salmon, may also be responsible. Regardless of the cause, these wide-spread phenotypic shifts influence fecundity and population abundance, and ultimately may put populations and associated fisheries at risk of decline.     

Atlantic salmon straying from the River Imsa

Mean estimated straying rate for Atlantic salmon Salmo salar L. leaving the River Imsa as smolts during 1976–1999 was 15% for hatchery fish and 6% for wild conspecifics. Hatchery Atlantic salmon selected for production traits during four or more generations strayed >50%. The straying rate was higher for Atlantic salmon staying 2 rather than 1 year at sea before attaining maturity. For spawning, 96% of the strays entered streams within 420 km from the River Imsa, and c . 80% entered streams within 60 km of the mouth of the River Imsa, whether the fish were wild or hatchery released. Within the 60 km zone, the number of strays caught in a river increased with the Atlantic salmon catch in that river, but there was no significant relationship between straying rate and water discharge or distance from the river to the River Imsa. The observed straying rate of hatchery Atlantic salmon decreased with increasing number of fish entering the River Imsa. Sexual maturation as parr did not influence the tendency to stray. The results suggest that the establishment of temporary zones, free of fish farms, outside important Atlantic salmon rivers by the fisheries authorities in Norway should be large, whole fjords, to be effective.     

Understanding the adaptive consequences of hatchery-wild interactions in Alaska salmon

About 31% of salmon harvested in Alaska comes from the hatchery production of hundreds of millions of pink and chum salmon and smaller numbers of sockeye, Chinook, and coho salmon. The numbers of hatchery-reared juveniles released in some areas are greater than the numbers of juveniles from wild populations. However, virtually nothing is known about the effects of hatchery fish on wild populations in Alaska. Possible effects of these interactions can be inferred from studies of salmonids in other areas, from studies of other animals, and from theory. Numerous studies show a complex relationship between the genetic architecture of a population and its environment. Adaptive responses to nature and anthropogenic selection can be influenced by variation at a single gene, or more often, by the additive effects of several genes. Studies of salmonids in other areas show that hatchery practices can lead to the loss of genetic diversity, to shifts in adult run timing and earlier maturity, to increases in parasite load, to increases in straying, to altered levels of boldness and dominance, to shifts in juvenile out-migration timing, and to changes in growth. Controlled experiments across generations show, and theory predicts, that the loss of adaptive fitness in hatchery salmon, relative to fitness in wild salmon, can occur on a remarkably short time scale. All of these changes can influence survival and impose selective regimes that influence genetically based adaptive traits. The preservation of adaptive potential in wild populations is an important buffer against diseases and climate variability and, hence, should be considered in planning hatchery production levels and release locations. The protection of wild populations is the foundation for achieving sustained harvests of salmon in Alaska.     

Relationship of size at return with environmental variation,hatchery production,and productivity of wild pink salmon in Prince William Sound,Alaska: does size matter?

Pink salmon (Oncorhynchus gorbuscha) returning to Prince William Sound (PWS), Alaska, have increased to historically high levels of abundance in recent years, but average body size at return has declined. We examined how body size at return of PWS pink salmon was related to 10 biophysical factors, including the scale of hatchery production. We also examined the effect of body size at return on productivity of wild pink salmon in PWS. For the 1975–1999 brood years, we found that an index of total abundance of pink salmon in the Gulf of Alaska and sea surface temperature during the year of return best explained the variation in pink salmon body size over time. Body size at return was significantly correlated with productivity of wild pink salmon. We used stepwise-regression to fit a generalized linear version of the Ricker spawner-recruit model to determine if body size would explain significant variation in wild-stock productivity in context with other environmental variation, including hatchery production. The results indicate that variability in wild-stock productivity is primarily driven by density-independent factors in the marine environment, but that body size of wild spawners also significantly affects productivity of wild PWS pink salmon. We conclude that the success of large-scale enhancement increasing the total run in PWS may have contributed to the decline in body size because of density-dependent growth in the Gulf of Alaska. We used a simulation model to estimate the impact of hatchery-induced changes in adult body size on wild-stock production in PWS. We estimated an annual wild-stock yield loss of 1.03 million pink salmon, less than 5% of the annual hatchery return of 24.2 million adult pink salmon for brood years 1990–1999.     

Recent Salmon Declines: A Result of Lost Feeding Opportunities Due to Bad Timing?

As the timing of spring productivity blooms in near-shore areas advances due to warming trends in global climate, the selection pressures on out-migrating salmon smolts are shifting. Species and stocks that leave natal streams earlier may be favoured over later-migrating fish. The low post-release survival of hatchery fish during recent years may be in part due to static release times that do not take the timing of plankton blooms into account. This study examined the effects of release time on the migratory behaviour and survival of wild and hatchery-reared coho salmon (Oncorhynchus kisutch) using acoustic and coded-wire telemetry. Plankton monitoring and near-shore seining were also conducted to determine which habitat and food sources were favoured. Acoustic tags (n = 140) and coded-wire tags (n = 266,692) were implanted into coho salmon smolts at the Seymour and Quinsam Rivers, in British Columbia, Canada. Differences between wild and hatchery fish, and early and late releases were examined during the entire lifecycle. Physiological sampling was also carried out on 30 fish from each release group. The smolt-to-adult survival of coho salmon released during periods of high marine productivity was 1.5- to 3-fold greater than those released both before and after, and the fish''s degree of smoltification affected their downstream migration time and duration of stay in the estuary. Therefore, hatchery managers should consider having smolts fully developed and ready for release during the peak of the near-shore plankton blooms. Monitoring chlorophyll a levels and water temperature early in the spring could provide a forecast of the timing of these blooms, giving hatcheries time to adjust their release schedule.     

Source-Sink Estimates of Genetic Introgression Show Influence of Hatchery Strays on Wild Chum Salmon Populations in Prince William Sound,Alaska

The extent to which stray, hatchery-reared salmon affect wild populations is much debated. Although experiments show that artificial breeding and culture influence the genetics of hatchery salmon, little is known about the interaction between hatchery and wild salmon in a natural setting. Here, we estimated historical and contemporary genetic population structures of chum salmon (Oncorhynchus keta) in Prince William Sound (PWS), Alaska, with 135 single nucleotide polymorphism (SNP) markers. Historical population structure was inferred from the analysis of DNA from fish scales, which had been archived since the late 1960’s for several populations in PWS. Parallel analyses with microsatellites and a test based on Hardy-Weinberg proportions showed that about 50% of the fish-scale DNA was cross-contaminated with DNA from other fish. These samples were removed from the analysis. We used a novel application of the classical source-sink model to compare SNP allele frequencies in these archived fish-scales (1964–1982) with frequencies in contemporary samples (2008–2010) and found a temporal shift toward hatchery allele frequencies in some wild populations. Other populations showed markedly less introgression, despite moderate amounts of hatchery straying. The extent of introgression may reflect similarities in spawning time and life-history traits between hatchery and wild fish, or the degree that hybrids return to a natal spawning area. The source-sink model is a powerful means of detecting low levels of introgression over several generations.