Inference of Potential Genetic Risks Associated with Large-Scale Releases of Red Sea Bream in Kanagawa Prefecture, Japan Based on Nuclear and Mitochondrial DNA Analysis

Since 1978, millions of hatchery-reared red sea bream (Pagrus major) juveniles have been released in Sagami Bay and Tokyo Bay in Kanagawa Prefecture, Japan. The stock enhancement program has contributed to total catch; however, no information regarding the genetic interactions with wild counterparts is available. Here, we combined 15 microsatellite loci and mitochondrial D-loop sequencing to characterize the genetic resources of red sea bream in Sagami Bay and Tokyo Bay and to elucidate the potential harmful genetic effects associated with fish releases. Both types of markers evidenced higher levels of genetic diversity in wild samples (SB and TB) compared with offspring before stocking (H07 and H08) as well as a hatchery-released sample recaptured in Sagami Bay (HR). Microsatellite F _ST estimates and Bayesian clustering analysis found significant genetic differences among samples (F _ST?=?0.013–0.054), except for the two wild samples (F _ST?=?0.002) and HR vs. H07 (F _ST?=?0.007). On the other hand, mitochondrial-based Ф _ST suggested haplotypic similarity between SB, H07, and HR. The low effective number of females contributing to the offspring over multiple generations may be responsible for the lack of haplotypic differentiation. Moreover, the putative hatchery origin to three fish (8 %) without deformity in the inter-nostril epidermis was inferred for the first time. Our results showed the usefulness of combining nuclear and mitochondrial markers to elucidate genetic interactions between hatchery-released and wild red sea bream and warned about potential harmful genetic effects should interbreeding takes place.     

Microsatellite assessment of the genetic diversity in indigenous populations of curimba (<Emphasis Type="Italic">Prochilodus argenteus</Emphasis>) in the São Francisco river (Brazil)

The freshwater fish curimba (Prochilodus argenteus) is an endemic species of the São Francisco River basin, with great aquaculture potential. The construction of several hydroelectric power dams along the river, and the pulsed releases of water from these dams altered and degraded the native fish habitats, which led to the development of a hatchery-reared fingerling restocking program. A comprehensive genetic baseline evaluation of the indigenous populations of curimba and of a hatchery stock was done using microsatellite markers. Pairwise F _ST values, Bayesian analysis and the number of migrants per generation were used to illustrate the genetic structure of the curimba populations along almost 3000 km of the river, suggesting the existence of three units of conservation: one in the Upper, a second in the Middle and a third including part of the Middle, Submiddle and Lower stretches. We have analyzed the genetic contribution of hatchery stock releases in two stretches of the river using individual admixture coefficients; and the results showed that admixture makes a negligible contribution to indigenous recruitment. We discussed about supplementation programs for this river from the perspective of three units of conservation and the risks associated with using domesticated fish.     

Do hatchery-reared sea urchins pose a threat to genetic diversity in wild populations?

In salmonids, the release of hatchery-reared fish has been shown to cause irreversible genetic impacts on wild populations. However, although responsible practices for producing and releasing genetically diverse, hatchery-reared juveniles have been published widely, they are rarely implemented. Here, we investigated genetic differences between wild and early-generation hatchery-reared populations of the purple sea urchin Paracentrotus lividus (a commercially important species in Europe) to assess whether hatcheries were able to maintain natural levels of genetic diversity. To test the hypothesis that hatchery rearing would cause bottleneck effects (that is, a substantial reduction in genetic diversity and differentiation from wild populations), we compared the levels and patterns of genetic variation between two hatcheries and four nearby wild populations, using samples from both Spain and Ireland. We found that hatchery-reared populations were less diverse and had diverged significantly from the wild populations, with a very small effective population size and a high degree of relatedness between individuals. These results raise a number of concerns about the genetic impacts of their release into wild populations, particularly when such a degree of differentiation can occur in a single generation of hatchery rearing. Consequently, we suggest that caution should be taken when using hatchery-reared individuals to augment fisheries, even for marine species with high dispersal capacity, and we provide some recommendations to improve hatchery rearing and release practices. Our results further highlight the need to consider the genetic risks of releasing hatchery-reared juveniles into the wild during the establishment of restocking, stock enhancement and sea ranching programs.     

Genetic differences between wild and hatchery populations of red sea cucumber (Stichopus japonicus) inferred from microsatellite markers: implications for production and stocking programs design

Red sea cucumber Stichopus japonicus is the most important and valuable commercial sea cucumber species in Korea. Its farming and stock enhancement started in the early 2000s and is still rapid expansion in Korea. Therefore, the analyses of genetic status of wild and hatchery populations are necessary to maintain the genetic diversity of this valuable marine resource. In this study, possible genetic similarity and differences between the wild population and hatchery population in Jeju, Korea were accessed using multiplex assays with eight highly polymorphic microsatellite loci. High levels of polymorphism were observed between the two populations. A total of 93 different alleles were found. Although a considerable loss of unique alleles and relatively high inbreeding coefficient value were observed in the hatchery samples, no statistically significant reductions were found in heterozygosity or allelic diversity in the hatchery population, compared with the wild population. However, significant genetic heterogeneity was found between two populations. These results suggest that genetic drift has probably promoted differentiation between populations, and stocking intensity in wild populations may correlate with loss of genetic integrity. Therefore, the sustainable exploitation plans of the fishery resource should be developed by applying basic genetic principles combined with molecular monitoring. This genetic baseline information of Korean red sea cucumber has important implications for designing of genetically sustainable restocking programs and more efficient conservation management guidelines for these valuable genetic materials.     

Genetic structure of the Korean black scraper Thamnaconus modestus inferred from microsatellite marker analysis

The Korean black scraper, Thamnaconus modestus, is one of the most economically important maricultural fish species in Korea. However, the annual catch of this fish has been continuously declining over the past several decades. In this study, the genetic diversity and relationships among four wild populations and two hatchery stocks of Korean black scraper were assessed based on 16 microsatellite (MS) markers. A total of 319 different alleles were detected over all loci with an average of 19.94 alleles per locus. The hatchery stocks [mean number of alleles (N _A) = 12, allelic richness (A _R) = 12, expected heterozygosity (He) = 0.834] showed a slight reduction (P > 0.05) in genetic variability in comparison with wild populations (mean N _A = 13.86, A _R = 12.35, He = 0.844), suggesting a sufficient level of genetic variation in the hatchery populations. Similarly low levels of inbreeding and significant Hardy–Weinberg equilibrium deviations were detected in both wild and hatchery populations. The genetic subdivision among all six populations was low but significant (overall F _ST = 0.008, P < 0.01). Pairwise F _ST, a phylogenetic tree, and multidimensional scaling analysis suggested the existence of three geographically structured populations based on different sea basin origins, although the isolation-by-distance model was rejected. This result was corroborated by an analysis of molecular variance. This genetic differentiation may result from the co-effects of various factors, such as historical dispersal, local environment and ocean currents. These three geographical groups can be considered as independent management units. Our results show that MS markers may be suitable not only for the genetic monitoring of hatchery stocks but also for revealing the population structure of Korean black scraper populations. These results will provide critical information for breeding programs, the management of cultured stocks and the conservation of this species.     

Fine-scale genetic structure derived from stocking black sea bream, Acanthopagrus schlegelii (Bleeker, 1854), in Hiroshima Bay, Japan

Black sea bream ( Acanthopagrus schlegelii ) is an important commercial and sport fishing species inhabiting Hiroshima Bay, where an intensive stock enhancement program is carried out for this species. In order to clarify the fine-scale genetic effects of the releases, black sea bream specimens were collected at five locations (Ninoshima, Atatajima, Miyajima, Oonasamijima and Kurahashi) in Hiroshima Bay. High homogeneity was observed among locations. The sample from Ninoshima, where stocking was most intense, presented the lowest number of alleles per locus (13.5) and showed significant differences in the pairwise F _ST value compared to the fish at Atatajima, Miyajima and Oonasamijima, but not significantly different from those collected at Kurahashi. However, all differences disappeared once analysis was performed standardizing the age-classes of all samples. The results suggest an important effect of the releases on genetic diversity of A. schlegelii in Hiroshima Bay. Moreover, the observed genetic population substructure is presumed to be related to the year-class composition of the samples at each location.     

Determination of genetic diversity of wild and cultured topmouth culter (Culter alburnus) inhabiting China using mitochondrial DNA and microsatellites

The topmouth culter (Culter alburnus) is one of the most commercially important freshwater fish species inhabiting China. However, very limited information is available regarding its genetic diversity and population structure, thus hindering the effective management of this fish stock. Understanding the genetic diversity of wild and cultured topmouth culter populations is highly relevant for successful hatchery management. This study evaluated the genetic diversity and structure of five wild and two cultured populations of topmouth culter in China by using microsatellites and mitochondrial DNA. The genetic diversity of wild populations was found to be lower than that of cultured populations. This finding indicates that wild topmouth culter resources should be protected to prevent further degeneration and extinction. Moreover, it demonstrated that cultured populations have greater breeding potential than wild ones. Subdivisions among wild populations were observed, which should be considered as different units for conservation and hatchery management.     

Mitochondrial DNA variation and population genetic structure in the small yellow croaker at the coast of Yellow Sea and East China Sea

Small yellow croaker is one of the most important fishery species in China. The mass–scale artificial propagation of this fish species was initially developed in 2015 with the aim of facilitating the fish production stock enhancement and aquaculture programs in the future. In the present study, the wild broodfish and its corresponding progeny along with three other wild populations were sampled and subjected to sequence analysis of the mitochondrial cytochrome c oxidase subunit I gene. The genetic diversity and population genetic structure were evaluated with a total sample size of 141 individuals representing the populations of the Yellow Sea (Qingdao and Lvsi populations) and the East China Sea (Xiangshan and Ningde populations). The wild populations were characterized by high haplotype diversity (0.925–0.976) and low nucleotide diversity (0.376%–0.560%). The hierarchical analysis of molecular variance (AMOVA) analysis and the values of pairwise Ф-statistics (Ф_ST) indicated non-significant genetic differentiation among the four wild populations. The hatchery stock XSH exhibited lower indices of genetic diversity compared with the wild populations that could be attributed to the small effective population size. The findings of the present study have valuable insight to the sustainable management and utilization of this resource.     

Genetic interactions between marine finfish species in European aquaculture and wild conspecifics

The principal species of marine aquaculture in Europe are Atlantic salmon (Salmo salar), sea bass (Dicentrarchus labrax) and sea bream (Sparus auratus). For Atlantic salmon and sea bass, a substantial part of total genetic variation is partitioned at the geographical population level. In the case of sea bream, gene flow across the Azores/Mediterranean scale appears to be extensive and population structuring is not detected. For Atlantic salmon and sea bass, natural population structure is at risk from genetic interaction with escaped aquaculture conspecifics. The locally adaptive features of populations are at risk from interbreeding with non‐local aquaculture fish. Wild populations, generally, are at risk from interactions with aquaculture fish that have been subject to artificial selection or domestication. Atlantic salmon is the main European aquaculture species and its population genetics and ecology have been well‐studied. A general case regarding genetic interactions can be based on the information available for salmon and extended to cover other species, in the appropriate context. A generalized flow chart for interactions is presented. Salmon escape from aquaculture at all life stages, and some survive to breed among wild salmon. Reproductive fitness in the escaped fish is lower than in native, wild fish because of behavioural deficiencies at spawning. However, as the number of salmon in aquaculture greatly exceeds the number of wild fish, even small fractional rates of escape may result in the local presence of large numbers, and high frequencies, of escaped fish. At present, policy and legislation in relation to minimizing genetic interactions between wild and aquaculture fish is best developed for Atlantic salmon, through the recommendations of the Oslo Agreement developed by the North Atlantic Salmon Conservation Organization and subsequent agreements on their implementation. In future, the potential use of genetically modified fish in aquaculture will make additional policy development necessary. Improved containment is recommended as the key to minimizing the numbers and therefore the effects of escaped fish. Emergency recovery procedures are recommended as a back‐up measure in the case of containment failure. Reproductive sterility is recommended as a future key to eliminating the genetic potential of escaped fish. The maintenance of robust populations of wild fish is recommended as a key to minimizing the effects of escaped fish on wild populations.     

The genetic structure of endangered indigenous populations of the amago salmon, <Emphasis Type="Italic">Oncorhynchus</Emphasis><Emphasis Type="Italic">masou</Emphasis><Emphasis Type="Italic">ishikawae</Emphasis>, in Japan

The amago salmon, Oncorhynchus masou ishikawae, is an endemic subspecies of O. masou in Japan. Owing to the extensive stocking of hatchery fish throughout Japan, indigenous populations of O. m. ishikawae are now on the verge of extinction. We examined the genetic effects of stocking hatchery fish on wild populations in the River Koza, Japan, using microsatellite and mitochondrial DNA (mtDNA) markers. For mtDNA, haplotype mt1, which is common in wild populations, was present exclusively in isolated wild populations assumed to be unaffected by previous stocking, while it was never observed in hatchery fish. Genetic diversity was much higher in wild populations in the stocked area, which shared many mtDNA haplotypes with hatchery fish, than in isolated wild populations with haplotype mt1. Pairwise F _ST estimates based on microsatellites showed significant differentiation among the isolated populations with many microsatellite loci monomorphic. Significant deviation from Hardy–Weinberg equilibrium was observed in wild populations in the area subject to stocking, where a Bayesian-based assignment test showed a high level of introgression with hatchery fish. These results suggest that wild populations with haplotype mt1, which became isolated through anthropogenic environmental change in the 1950–1960s, represent indigenous populations of O. m. ishikawae in the River Koza. They have low genetic diversity, most likely caused by genetic bottlenecks following damming and environmental deterioration, while stocking of hatchery fish over the past 30 years apparently had a large impact on the genetic structure of wild populations in the main channel of the River Koza.     

Randomly amplified polymorphic DNA analysis of four different populations of the Indian major carp, Labeo rohita (Hamilton)

The level of genetic variation provides the raw material for selective improvement of a stock. Random amplified polymorphic DNA (RAPD) assay was used to assess the genetic variation in three rivers: the Halda, the Jamuna and the Padma as well as in one hatchery population of the commercially important Indian major carp, Labeo rohita. RAPD markers were amplified from DNA samples of 35 fish from each of the four populations using six decamer random primers. The polymorphic loci proportions were 0.33, 0.28, 0.28 and 0.26 and Nei's gene diversity values were 0.06, 0.07, 0.06 and 0.05 for the Halda, the Jamuna, the Padma and the hatchery populations, respectively. The pairwise population differentiation (F_ST) values indicated a low level of genetic differentiation between the population pairs. From the unweighted pair group method of arithmetic mean (UPGMA) dendrogram based on Nei's genetic distances a correlation between genetic affinities and geographical area was found. The populations were segregated into two groups: the Halda in one group and the Jamuna, the Padma and the hatchery in another group. Overall, the RAPD technique can be introduced as a tool in the population genetics of the rohu fish to provide information on their genetic stock structure.     

Genetic diversity and differentiation of the Korean starry flounder (Platichthys stellatus) between and within cultured stocks and wild populations inferred from microsatellite DNA analysis

The Korean starry flounder, Platichthys stellatus, is economically valuable coastal resident fish species. However, the annual catch of this fish has fluctuated and suffered major declines in Korea. We examined the genetic diversity and population structure for four wild populations and three hatchery stocks of Korean starry flounder to protect its genetic integrity using nine microsatellites. A group of 339 genotypes belonging to seven populations were screened. High degrees of polymorphism at the microsatellite loci were observed within both the wild and hatchery populations. Compared to the wild populations, genetic changes, including reduced genetic diversity and highly significant differentiation, have occurred in cultured stocks. Significant population differentiation was also observed in wild starry flounder populations. Similar degrees of inbreeding and significant Hardy–Weinberg equilibrium deviations were detected in both the wild and the hatchery populations. The genetic connectivity pattern identified four distinct metapopulations of starry flounder in Korea by clustering in the phylogenetic tree, Bayesian analyses, molecular variance analysis, PCA and multidimensional scaling analysis. A pattern of isolation-by-distance was not significant. This genetic differentiation may be the result of the co-effects of various factors, such as historic dispersal, local environment or anthropogenic activities. These results provide useful information for the genetic monitoring of P. stellatus hatchery stocks, for the genetic improvement of this species by selective breeding and for designing suitable management guidelines for the conservation of this species.     

Molecular dating of a marine species,Eriocheir japonica (Decapoda: Grapsidae), corroborates cenozoic tectonic events and sea level fluctuation

Changes of coastal topography for Cenozoic Himalayan orogeny complicated the phylogeographical structure of marine species and deepened their divergences. To test the association between divergence and Cenozoic tectonic events, we analyzed the phylogeographical structure of Eriocheir japonica by combining molecular data and geographical environment events. The four distinct lineages obtained through phylogenetic reconstruction and network analysis demonstrated the significant genetic divergence among geographical populations. Furthermore, the divergence time between E. j. japonica in Japan and E. j. sinensis in China was about 10.5–11.5 mya, which was coincident with the opening of the Sea of Japan. The north-south divergence time (15.5–17.5 mya) was in the range of the occurrence of the Himalaya movement. We hypothesize that coastal topography, including the formation of Taiwan in the Himalaya movement and the opening of the Sea of Japan, contributed to the geographical subspeciation of marine species. Mitten crabs were inferred to originate from one ancient population with the oldest haplotype H6 and subsequently divide into northern and southern populations. Furthermore, the Japan lineage derived from northern population in China for the opening of the Sea of Japan.     

Genetic differences between wild and hatchery populations ofDiplodus sargus andD. vulgaris inferred from RAPD markers: implications for production and restocking programs design

Restocking and stock enhancement programs are now recognized as an important tool for the management of fishery resources. It is important, however, to have an adequate knowledge on the genetic population structure of both the released stock and the wild population before carrying out such programs. In this study, random amplified polymorphic DNA (RAPD) markers were applied to assess genetic diversity and population structure of wild and hatchery populations of the white seabreamDiplodus sargus and the common two-banded seabreamD. vulgaris (Sparidae). The estimated values for intrapopulation genetic variation, measured using the percentage of polymorphic loci (%P), Shannon indexH’, and Nei’s gene diversity (h), showed high values for all populations. The percentage of genetic variation withinD. sargus andD. vulgaris populations, based on coefficient of gene differentiation, reached 82.5% and 90% of the total genetic variation, respectively. An undeniable decrease in genetic variation was found in both hatchery populations, particularly inD. sargus, compared to the wild ones. However, the high values of variation within all populations and the low levels of genetic variation among populations did not indicate inbreeding or depression effects, thus indicating a fairly proper hatchery management. Nevertheless, the results of this study highlight the importance of monitoring the genetic variation of hatchery populations, particularly those to be used in restocking programs. The creation of a genetic baseline database will contribute to a more efficient conservation management and to the design of genetically sustainable restocking programs.     

Genetic structure of three marine fishes from the Gulf of Pagasitikos (Greece) based on allozymes, RAPD, and mtDNA RFLP markers

In the present work we used three molecular techniques (allozymes, RAPDs and mtDNA RFLPs) in order to study the genetic structure of three commercial marine species (Mullus surmuletus, Mullus barbatus, and Pagellus erythrinus). Each species was sampled from three locations within the Gulf of Pagasitikos, Greece and from two neighbouring locations outside the Gulf (Trikeri and Alonissos). Values of genetic heterozygosity and nucleotide diversity for all populations studied were similar or above the mean values observed in marine fishes. None of the three types of molecular markers used revealed diagnostic patterns, which could allow the allocation of individuals to one of the populations. The analyses revealed that the three populations within Pagasitikos were homogenous representing thus a panmictic stock. However, there were evidences of genetic population subdivision between localities from inside and outside of the Pagasitikos Gulf. The results provide essential information for the design of a sustainable management plan of the Gulf of Pagasitikos and its demersal fish resources.     

Population genetics,conservation and evolution in salmonids and other widely cultured fishes: some perspectives over six decades

This paper explores my shifting understandings of interactions primarily between salmonid fish culture and fish conservation during the latter half of the 20th century. The idea that conspecific natural and cultured fish were largely interchangeable among phenotypically similar populations began to change with the advent of molecular genetic markers. With the gradual clarification of major geographic lineages beginning in the 1970s came awareness that translocations among anadromous lineages were generally destined for failure; in contrast, gene flow more readily occurred among non-anadromous lineages and sometimes, species. Within lineages, data concurrently were accumulating that showed adaptations to their respective environments distinguished cultured and wild populations. Reduced obstacles to gene flow at this level often resulted in homogenizations among wild and cultured fish in areas where widespread hatchery releases occurred; conversely, adaptive radiations in vacant habitats sometimes occurred over a few decades from single source hatchery releases. Current ideas relating to salmonid interbreeding, population substructure and culture evolved from these observations. Among lineages, resistance to gene flow is much greater between anadromous than purely freshwater populations or species. Within lineages, ease of gene flow in both anadromous and freshwater populations is problematical with regard to cultured and wild populations because large-scale supplementation programs erode local adaptations and fine-scale population substructures. At this level, a potential ability to regenerate natural substructure upon relaxation of supplementation is offset by uncertainties of time scales and intrinsic capabilities of homogenized populations. However, management that separates harvest and reproduction of wild and cultured subpopulations can minimize these losses. Some generality of this strategy to other fishes is supported by losses of local adaptations and outbreeding depression in black basses following population admixtures that parallel those observed in salmonids.     

Contrasting Genetic Structure among Populations of Two Amphidromous Fish Species (Sicydiinae) in the Central West Pacific

Both present-day and past processes can shape connectivity of populations. Pleistocene vicariant events and dispersal have shaped the present distribution and connectivity patterns of aquatic species in the Indo-Pacific region. In particular, the processes that have shaped distribution of amphidromous goby species still remain unknown. Previous studies show that phylogeographic breaks are observed between populations in the Indian and Pacific Oceans where the shallow Sunda shelf constituted a geographical barrier to dispersal, or that the large spans of open ocean that isolate the Hawaiian or Polynesian Islands are also barriers for amphidromous species even though they have great dispersal capacity. Here we assess past and present genetic structure of populations of two amphidromous fish (gobies of the Sicydiinae) that are widely distributed in the Central West Pacific and which have similar pelagic larval durations. We analysed sections of mitochondrial COI, Cytb and nuclear Rhodospine genes in individuals sampled from different locations across their entire known range. Similar to other Sicydiinae fish, intraspecific mtDNA genetic diversity was high for all species (haplotype diversity between 0.9–0.96). Spatial analyses of genetic variation in Sicyopus zosterophorum demonstrated strong isolation across the Torres Strait, which was a geologically intermittent land barrier linking Australia to Papua New Guinea. There was a clear genetic break between the northwestern and the southwestern clusters in Si. zosterophorum (φ_ST = 0.67502 for COI) and coalescent analyses revealed that the two populations split at 306 Kyr BP (95% HPD 79–625 Kyr BP), which is consistent with a Pleistocene separation caused by the Torres Strait barrier. However, this geographical barrier did not seem to affect Sm. fehlmanni. Historical and demographic hypotheses are raised to explain the different patterns of population structure and distribution between these species. Strategies aiming to conserve amphidromous fish should consider the presence of cryptic evolutionary lineages to prevent stock depletion.     

Variation in the Early Marine Survival and Behavior of Natural and Hatchery-Reared Hood Canal Steelhead

Background

Hatchery-induced selection and direct effects of the culture environment can both cause captively bred fish populations to survive at low rates and behave unnaturally in the wild. New approaches to fish rearing in conservation hatcheries seek to reduce hatchery-induced selection, maintain genetic resources, and improve the survival of released fish.

Methodology/Principal Findings

This study used acoustic telemetry to compare three years of early marine survival estimates for two wild steelhead populations to survival of two populations raised at two different conservation hatcheries located within the Hood Canal watershed. Steelhead smolts from one conservation hatchery survived with probabilities similar to the two wild populations (freshwater: 95.8–96.9%, early marine: 10.0–15.9%), while smolts from the other conservation hatchery exhibited reduced freshwater and early marine survival (freshwater: 50.2–58.7%, early marine: 2.6–5.1%). Freshwater and marine travel rates did not differ significantly between wild and hatchery individuals from the same stock, though hatchery smolts did display reduced migration ranges within Hood Canal. Between-hatchery differences in rearing density and vessel geometry likely affected survival and behavior after release and contributed to greater variation between hatcheries than between wild populations.

Conclusions/Significance

Our results suggest that hatchery-reared smolts can achieve early marine survival rates similar to wild smolt survival rates, and that migration performance of hatchery-reared steelhead can vary substantially depending on the environmental conditions and practices employed during captivity.     

Factors that contribute to the ecological risks of salmon and steelhead hatchery programs and some mitigating strategies

State and federal agencies in the United States annually release millions of hatchery salmon and steelhead into public waters. Many of the hatchery programs are located in areas where the wild populations are now listed under the U.S. Endangered Species Act (ESA) (16 U.S.C. §§ 1531–1544). These hatchery programs pose genetic and ecological risks to wild fish populations. Genetic risks occur when hatchery and wild fish interbreed and usually occur within a taxonomic species. Ecological risks occur when the presence of hatchery fish affects how wild fish interact with their environment or with other species and may affect whole species assemblages. This paper reviews some of the factors that contribute to ecological risks. Important contributing factors include the relative abundance of hatchery and wild fish in natural production areas, hatchery programs that increase density-dependant mortality, residual hatchery fish, some physical advantages that hatchery fish can have over wild fish, and life history characteristics that may make some species especially vulnerable to the effects of ecological risks. Many of these risk factors can be mitigated by management activities that reduce the level of interactions between hatchery and wild fish. This paper concludes by recommending twelve mitigation strategies that may be useful when agencies need to bring hatchery programs into compliance with the take provisions of the ESA.     

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.