Insights on the concept of indicator populations derived from parentage‐based tagging in a large‐scale coho salmon application in British Columbia,Canada

For Pacific salmon, the key fisheries management goal in British Columbia (BC) is to maintain and restore healthy and diverse Pacific salmon populations, making conservation of salmon biodiversity the highest priority for resource management decision‐making. Salmon status assessments are often conducted on coded‐wire‐tagged subsets of indicator populations based on assumptions of little differentiation within or among proximal populations. In the current study of southern BC coho salmon (Oncorhynchus kisutch) populations, parentage‐based tagging (PBT) analysis provided novel information on migration and life‐history patterns to test the assumptions of biological homogeneity over limited (generally < 100 km) geographic distances and, potentially, to inform management of fisheries and hatchery broodstocks. Heterogeneity for location and timing of fishery captures, family productivity, and exploitation rate was observed over small geographic scales, within regions that are, or might be expected to be, within the area encompassed by a single‐tagged indicator population. These results provide little support for the suggestion that information gained from tagged indicator populations is representative of marine distribution, productivity, and exploitation patterns of proximal populations.     

Fecundity and egg size variation in North American Pacific salmon (Oncorhynchus)

We examined regional and latitudinal variation in fecundity and egg weight for five species of Pacific salmon ( Oncorhynchus ) along the Pacific coast of North America. Data were examined for 24 chum salmon, 15 pink salmon, 34 sockeye salmon, 44 chinook salmon, and 40 coho salmon populations from published sources, unpublished Canadian hatchery records, our own laboratory investigations, and other unpublished sources. Substantial regional variation in fecundity and egg weight was observed, with salmon on the Queen Charlotte Islands and Vancouver Island in British Columbia generally having lower fecundity and larger egg size than nearby mainland populations. The relative distance of freshwater migration to the spawning grounds generally had a marked effect on both fecundity and egg size, with populations spawning in the upper portions in the drainages of large rivers like the Fraser River in British Columbia having reduced fecundity and egg size compared with coastal spawning populations. Fecundity was generally higher and egg size generally lower in more northern populations of sockeye, chinook, and coho salmon compared with southern ones. We suggest that egg size tends to be lower in northern populations of some species as a result of increased fecundity due to their older ages at maturity and a limited amount of energy that can be expended on egg production.     

Genetic versus Rearing-Environment Effects on Phenotype: Hatchery and Natural Rearing Effects on Hatchery- and Wild-Born Coho Salmon

With the current trends in climate and fisheries, well-designed mitigative strategies for conserving fish stocks may become increasingly necessary. The poor post-release survival of hatchery-reared Pacific salmon indicates that salmon enhancement programs require assessment. The objective of this study was to determine the relative roles that genotype and rearing environment play in the phenotypic expression of young salmon, including their survival, growth, physiology, swimming endurance, predator avoidance and migratory behaviour. Wild- and hatchery-born coho salmon adults (Oncorhynchus kisutch) returning to the Chehalis River in British Columbia, Canada, were crossed to create pure hatchery, pure wild, and hybrid offspring. A proportion of the progeny from each cross was reared in a traditional hatchery environment, whereas the remaining fry were reared naturally in a contained side channel. The resulting phenotypic differences between replicates, between rearing environments, and between cross types were compared. While there were few phenotypic differences noted between genetic groups reared in the same habitat, rearing environment played a significant role in smolt size, survival, swimming endurance, predator avoidance and migratory behaviour. The lack of any observed genetic differences between wild- and hatchery-born salmon may be due to the long-term mixing of these genotypes from hatchery introgression into wild populations, or conversely, due to strong selection in nature—capable of maintaining highly fit genotypes whether or not fish have experienced part of their life history under cultured conditions.     

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.     

Minisatellite DNA variation and stock identification of coho salmon

Geographic variation in minisatellite DNA variation was examined in 18 stocks of coho salmon Oncorhynchus kisutch from British Columbia and three stocks from Kamchatka or Western Alaska. Genomic DNA was restricted with Mbo I or Hae III and hybridized with two minisatellite probes (p Ssa -A34, Ots PBS-1). Allele frequencies and DNA band counts derived from the two probes were combined with band counts from the probe Ssa to show a regional stock structure. In British Columbia, stocks from the Fraser River were distinct from those on Vancouver Island, and all were differentiated from those on the mainland of British Columbia. Average heterozygosity at the Ssa -A34 locus was 71%. Compared with a previous study of British Columbia coho salmon population structure in which variation at 26 allozyme loci was examined, greater population differentiation and higher heterozygosity were observed at minisatellite loci. Estimated stock compositions of simulated mixtures of fishery samples from British Columbia stocks were accurate and precise, with the potential of identifying stocks within the drainage basin of a major river, the Fraser River. Minisatellite DNA variation may provide accurate and precise estimates of stock composition in actual fishery applications, and has the potential of identifying individual fish to region or stock of origin.     

Have Native Coho Salmon (Oncorhynchus Kisutch) Persisted in the Nooksack and Samish rivers Despite Continuous Hatchery Production Throughout the Past Century?

For over a century, Washington State Department of Fish and Wildlife has implemented hatchery programs as a means to boost salmon abundance. Concerns have developed that native populations may be replaced by hatchery strains, decreasing the genetic diversity required to respond to environmental changes. We report a comparison of microsatellite DNA variation in wild-spawning and hatchery-strain coho salmon from the Nooksack and Samish rivers in northern Puget Sound. Significant heterogeneity in genotype frequencies was detected between wild-spawning coho salmon from the upper North Fork (NF) Nooksack River and hatchery-strain coho salmon from the Nooksack River (descendants of primarily Nooksack River broodstock). Little difference in genotype frequencies was detected between wild-spawning coho salmon from the Samish River and hatchery-strain coho salmon from the Nooksack River. The 13-locus suite provided high resolution: in assignment tests over 85% of wild-spawning coho salmon from the upper NF Nooksack River were assigned to source. Wild-spawning coho salmon collected below hatcheries in the Nooksack River and 50% of wild-spawning Samish River coho salmon were assigned to hatchery collections. The genetic divergence of wild-spawning coho salmon in the upper NF Nooksack River is remarkable given the extensive stocking history and proximity of a hatchery. We suggest that these upper river fish are native coho salmon and that wild spawners in the lower Nooksack and Samish River are descendants of hatchery productions. We attribute divergence to earlier run timing in upper NF Nooksack River wild spawners, availability of extensive spawning and rearing habitat upstream of a hatchery in the upper NF Nooksack River, and a longer stocking history in the Samish River.     

Temporal patterns in adult salmon migration timing across southeast Alaska

Pacific salmon migration timing can drive population productivity, ecosystem dynamics, and human harvest. Nevertheless, little is known about long‐term variation in salmon migration timing for multiple species across broad regions. We used long‐term data for five Pacific salmon species throughout rapidly warming southeast Alaska to describe long‐term changes in salmon migration timing, interannual phenological synchrony, relationships between climatic variation and migratory timing, and to test whether long‐term changes in migration timing are related to glaciation in headwater streams. Temporal changes in the median date of salmon migration timing varied widely across species. Most sockeye populations are migrating later over time (11 of 14), but pink, chum, and especially coho populations are migrating earlier than they did historically (16 of 19 combined). Temporal trends in duration and interannual variation in migration timing were highly variable across species and populations. The greatest temporal shifts in the median date of migration timing were correlated with decreases in the duration of migration timing, suggestive of a loss of phenotypic variation due to natural selection. Pairwise interannual correlations in migration timing varied widely but were generally positive, providing evidence for weak region‐wide phenological synchrony. This synchrony is likely a function of climatic variation, as interannual variation in migration timing was related to climatic phenomenon operating at large‐ (Pacific decadal oscillation), moderate‐ (sea surface temperature), and local‐scales (precipitation). Surprisingly, the presence or the absence of glaciers within a watershed was unrelated to long‐term shifts in phenology. Overall, there was extensive heterogeneity in long‐term patterns of migration timing throughout this climatically and geographically complex region, highlighting that future climatic change will likely have widely divergent impacts on salmon migration timing. Although salmon phenological diversity will complicate future predictions of migration timing, this variation likely acts as a major contributor to population and ecosystem resiliency in southeast Alaska.     

Idiosyncratic responses of Pacific salmon species to land cover,fragmentation, and scale

Salmon are critical to the ecology and livelihood of the Pacific Northwest, and are declining throughout much of their range. While much of their life cycle occurs in open ocean, freshwater conditions also contribute to population trends. Because stream habitats are connected to uplands by water flow, salmon can be influenced by the characteristics of terrestrial systems. We analyzed the relationships between the population trends of Pacific salmon (1953–2006) and land cover, fragmentation, and forest age derived from remotely‐sensed, landscape level datasets. Analyses included 425 populations of all native salmon species in 156 watersheds on Vancouver Island, British Columbia, Canada. Vancouver Island salmon escapements exhibited general patterns of decline, which may be largely controlled by broad‐scale marine conditions. The spatial variation in these population trends was related to landscape variables at watershed and riparian scales with regression trees. Results were found to be species specific, but characteristics indicating a legacy of historic and current forest management (such as fragmented forests and non‐forested or early‐successional forest cover) generally had negative effects, driven by a small subset of highly fragmented watersheds. Chum and coho had strong negative relationships with fragmentation, pink had a strong positive relationship with wetland abundance, and Chinook and sockeye were most closely related to geomorphology. There was no ‘single best’ scale of analysis. Salmon trends were generally more closely related to variables estimated over the entire watershed, however, the relative importances of watershed and riparian level predictors varied by both variable and species. Efforts to restore salmon habitat will be complicated by marine and freshwater processes, terrestrial conditions throughout watersheds, and the idiosyncratic requirements of each species.     

Using parentage analysis to estimate rates of straying and homing in Chinook salmon (Oncorhynchus tshawytscha)

We used parentage analysis based on microsatellite genotypes to measure rates of homing and straying of Chinook salmon (Oncorhynchus tshawytscha) among five major spawning tributaries within the Wenatchee River, Washington. On the basis of analysis of 2248 natural‐origin and 11594 hatchery‐origin fish, we estimated that the rate of homing to natal tributaries by natural‐origin fish ranged from 0% to 99% depending on the tributary. Hatchery‐origin fish released in one of the five tributaries homed to that tributary at a far lower rate than the natural‐origin fish (71% compared to 96%). For hatchery‐released fish, stray rates based on parentage analysis were consistent with rates estimated using physical tag recoveries. Stray rates among major spawning tributaries were generally higher than stray rates of tagged fish to areas outside of the Wenatchee River watershed. Within the Wenatchee watershed, rates of straying by natural‐origin fish were significantly affected by spawning tributary and by parental origin: progeny of naturally spawning hatchery‐produced fish strayed at significantly higher rates than progeny whose parents were themselves of natural origin. Notably, none of the 170 offspring that were products of mating by two natural‐origin fish strayed from their natal tributary. Indirect estimates of gene flow based on F_ST statistics were correlated with but higher than the estimates from the parentage data. Tributary‐specific estimates of effective population size were also correlated with the number of spawners in each tributary.     

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.     

Overview of salmon stock enhancement in southeast Alaska and compatibility with maintenance of hatchery and wild stocks

Modern salmon hatcheries in Southeast Alaska were established in the 1970s when wild runs were at record low levels. Enhancement programs were designed to help rehabilitate depressed fisheries and to protect wild salmon stocks through detailed planning and permitting processes that included focused policies on genetics, pathology, and management. Hatcheries were located away from significant wild stocks, local sources were used to develop hatchery broodstocks, and juveniles are marked so management can target fisheries on hatchery fish. Initially conceived as a state-run system, the Southeast Alaska (SEAK) program has evolved into a private, non-profit concept centered around regional aquaculture associations run by fishermen and other stakeholders that pay for hatchery operations through landing fees and sale of fish. Today there are 15 production hatcheries and 2 research hatcheries in SEAK that between 2005 and 2009 released from 474 to 580 million (average 517 million) juvenile salmon per year. During this same period commercial harvest of salmon in the region ranged from 28 to 71 million salmon per year (average 49 million). Contributions of hatchery-origin fish to this harvest respectively averaged 2%, 9%, 19%, 20%, and 78% for pink, sockeye, Chinook, coho, and chum salmon. Both hatchery and wild salmon stocks throughout much of Alaska have experienced high marine survivals since the 1980s and 1990s resulting in record harvests over the past two decades. Although some interactions between hatchery salmon and wild salmon are unavoidable including increasing concerns over straying of hatchery fish into wild salmon streams, obvious adverse impacts from hatcheries on production of wild salmon populations in this region are not readily evident.     

Using grizzly bears to assess harvest-ecosystem tradeoffs in salmon fisheries

Implementation of ecosystem-based fisheries management (EBFM) requires a clear conceptual and quantitative framework for assessing how different harvest options can modify benefits to ecosystem and human beneficiaries. We address this social-ecological need for Pacific salmon fisheries, which are economically valuable but intercept much of the annual pulse of nutrient subsidies that salmon provide to terrestrial and aquatic food webs. We used grizzly bears, vectors of salmon nutrients and animals with densities strongly coupled to salmon abundance, as surrogates for "salmon ecosystem" function. Combining salmon biomass and stock-recruitment data with stable isotope analysis, we assess potential tradeoffs between fishery yields and bear population densities for six sockeye salmon stocks in Bristol Bay, Alaska, and British Columbia (BC), Canada. For the coastal stocks, we find that both bear densities and fishery yields would increase substantially if ecosystem allocations of salmon increase from currently applied lower to upper goals and beyond. This aligning of benefits comes at a potential cost, however, with the possibility of forgoing harvests in low productivity years. In contrast, we detect acute tradeoffs between bear densities and fishery yields in interior stocks within the Fraser River, BC, where biomass from other salmon species is low. There, increasing salmon allocations to ecosystems would benefit threatened bear populations at the cost of reduced long-term yields. To resolve this conflict, we propose an EBFM goal that values fisheries and bears (and by extension, the ecosystem) equally. At such targets, ecosystem benefits are unexpectedly large compared with losses in fishery yields. To explore other management options, we generate tradeoff curves that provide stock-specific accounting of the expected loss to fishers and gain to bears as more salmon escape the fishery. Our approach, modified to suit multiple scenarios, provides a generalizable method to resolve conflicts over shared resources in other systems.     

Salmon species, density and watershed size predict magnitude of marine enrichment in riparian food webs

Resource subsidies across habitat boundaries can structure recipient communities and food webs. In the northern Pacific region, bears Ursus spp. foraging on anadromous salmon Oncorhynchus spp. provide a key link between marine and terrestrial ecosystems, with salmon density, fish size and watershed size as potential predictors of the magnitude of marine subsidy to terrestrial habitats. We use nitrogen and carbon stable isotopes to provide an assessment of the patterns of marine‐enrichment in riparian plants (11 species, 4 guilds) and litter invertebrates (4 guilds) sampled from 27 watersheds in coastal British Columbia, Canada. Watersheds occurred in three geographical regions (Vancouver Island, mainland midcoast and Haida Gwaii) and varied in size, and in biomass (kg m^?1 of spawning length) and species of salmon (chum O. keta, pink O. gorbuscha and coho O. kisutch). δ¹⁵N values in all plant species and invertebrate guilds were positively predicted by total salmon biomass (kg m^?1) and negatively predicted by watershed size. We observed replicated parallel slopes among plant species and invertebrate guilds across the gradient in salmon biomass, with differences in means hypothesized to be due to plant fractionation and animal trophic position. As such, we derived a watershed δ¹⁵N‐index averaged across guilds, and using an information theoretic approach we find that the biomass of chum salmon is a much stronger predictor of the δ¹⁵N‐index than either pink or coho salmon, or the sum biomass of all species. The top linear model contained chum biomass and watershed size. Chum salmon biomass independently predicted δ¹⁵N‐index variation in all three regions of British Columbia. Chum salmon are larger than pink or coho and provide an energetic reward for bears that facilitates carcass transfer, tissue selective foraging, and nutrient distribution by insect scavengers. Analyses of biodiversity and habitat data across many watersheds moves towards a long‐term goal in fisheries ecology to better integrate ecosystem values in salmon conservation.     

Genetic population structure of central Oregon Coast coho salmon (<Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis>)

We surveyed microsatellite variation from 22 spawning populations of coho salmon (Oncorhynchus kisutch) from the Oregon Coast to help identify populations for conservation planning. All of our samples were temporally replicated, with most samples obtained in 2000 and 2001. We had three goals: (1) to confirm the status of populations identified on the basis of spawning location and life history; (2) to estimate effective population sizes and migration rates in order to determine demographic independence at different spatial scales; and (3) to determine if releases of Washington hatchery coho salmon in the 1980's into Oregon Coast streams resulted in measurable introgression into nearby wild Oregon Coast coho populations. For the last question, our study included a hatchery broodstock sample from 1985, after the Puget Sound introduction, and a 1975 sample taken from the same area prior to the introduction. Our results generally supported previously hypothesized population structure. Most importantly, we found unique lake-rearing groups identified on the basis of a common life-history type were genetically related. Estimates of immigrant fraction using several different methods also generally supported previously identified populations. Estimates of effective population size were highly correlated with estimates of spawning abundance. The 1985 hatchery sample was genetically similar to contemporary Washington samples, and the contemporary Oregon Coast samples were similar to the 1975 Oregon Coast sample, suggesting that introductions of Washington coho salmon did not result in large scale introgression into Oregon populations.     

Discriminating coho salmon (Oncorhynchus kisutch) populations within the Fraser River, British Columbia, using microsatellite DNA markers

Three microsatellite loci were used to examine genetic variation among 16 coho salmon ( Oncorhynchus kisutch ) populations within the Fraser River drainage system, in British Columbia, Canada. Each locus was highly polymorphic with 30 alleles at the Ots 101 locus, 15 alleles at the Ots 3 locus and 38 alleles at the Ots 103 locus. Average observed heterozygosities were 86.1%, 70%, and 56.1%, respectively. With the exception of the Dunn and Lemieux River populations, Chi-square tests and F _ST values indicated that all populations had significantly different allele frequencies. Two distinct population groups within the Fraser River drainage were observed. Lower Fraser River populations were strongly differentiated from populations spawning in the upper Fraser River, which includes the Thompson River (a tributary flowing into the upper Fraser) and the portion of the Fraser River beyond the precipitous Fraser River canyon. This regional population structure may have resulted from colonization of the upper and lower Fraser River regions by different founder populations following Pleistocene glaciation, and be maintained by adaptive differences between the two groups of coho salmon. Coho salmon populations in the upper Fraser and Thompson River drainages form an evolutionarily significant unit (ESU) of importance for conservation of biodiversity in coho salmon. Microsatellite DNA loci show promise as technically simple and highly informative genetic markers for coho salmon population management.     

Juvenile Salmon Usage of the Skeena River Estuary

Migratory salmon transit estuary habitats on their way out to the ocean but this phase of their life cycle is more poorly understood than other phases. The estuaries of large river systems in particular may support many populations and several species of salmon that originate from throughout the upstream river. The Skeena River of British Columbia, Canada, is a large river system with high salmon population- and species-level diversity. The estuary of the Skeena River is under pressure from industrial development, with two gas liquefaction terminals and a potash loading facility in various stages of environmental review processes, providing motivation for understanding the usage of the estuary by juvenile salmon. We conducted a juvenile salmonid sampling program throughout the Skeena River estuary in 2007 and 2013 to investigate the spatial and temporal distribution of different species and populations of salmon. We captured six species of juvenile anadromous salmonids throughout the estuary in both years, and found that areas proposed for development support some of the highest abundances of some species of salmon. Specifically, the highest abundances of sockeye (both years), Chinook in 2007, and coho salmon in 2013 were captured in areas proposed for development. For example, juvenile sockeye salmon were 2–8 times more abundant in the proposed development areas. Genetic stock assignment demonstrated that the Chinook salmon and most of the sockeye salmon that were captured originated from throughout the Skeena watershed, while some sockeye salmon came from the Nass, Stikine, Southeast Alaska, and coastal systems on the northern and central coasts of British Columbia. These fish support extensive commercial, recreational, and First Nations fisheries throughout the Skeena River and beyond. Our results demonstrate that estuary habitats integrate species and population diversity of salmon, and that if proposed development negatively affects the salmon populations that use the estuary, then numerous fisheries would also be negatively affected.     

Strategies for reducing the ecological risks of hatchery programs: Case studies from the Pacific Northwest

The Pacific Northwest state and federal agencies and tribes that operate salmon and steelhead (Oncorhynchus sp.) hatcheries are authorized to develop and implement strategies to reduce the risks the programs pose to wild fish populations. This paper reviews five case studies from the states of Oregon and Washington, USA, where agencies and tribes have implemented or proposed programs that were intended to reduce ecological risks due to hatchery programs. The case studies are for Oregon coho salmon, Select Area terminal fisheries programs for Chinook and coho salmon in the lower Columbia River, Hood Canal chum salmon in Puget Sound Washington, Siletz River steelhead on the Oregon coast, and Okanogan River Chinook salmon in eastern Washington. The five case studies address a diversity of management objectives and species. They demonstrate some of the science and risk reduction strategies used to alleviate the ecological effects of hatcheries, and they document some of the results and outcomes of taking action. Elements of four of the case studies have been in place for nearly 20 years. The available science and the conservation ethic toward hatchery programs evolved significantly over this period, and management decisions and strategies have been influenced by public policy as well as by scientific information. Therefore the case studies also document some of the history, the evolution of ideas, the uncertainty, and the political controversy associated with the management of this risk factor. The paper concludes with six principles to help guide the development of future risk reduction programs.     

The use of chemical cues in the upstream migration of coho salmon, Oncorhynchus kisutch Walbaum

The migratory behaviour of coho salmon was studied in the field. Coho salmon, Oncorhynchus kisutch , exposed to synthetic odours in a hatchery and released into Lake Michigan as juveniles, were recaptured as migrating adults 18 months later. The movements of 43 individuals were followed in experiments examining the role of imprinted chemical cues in the homing migration. Movements in relation to controlled distributions of the imprinting odours revealed that chemical cues are used by the salmon in their upstream migration. Acting with the rheotactic response, fish were guided upstream by imprinting odours simulating their home stream. Coho salmon, in the absence of their imprinting odour, respond negatively to the current. Differential responses to current appear to serve in segregating fish imprinted to odours of different home streams.     

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     

Conservation planning for freshwater–marine carryover effects on Chinook salmon survival

Experiences of migratory species in one habitat may affect their survival in the next habitat, in what is known as carryover effects. These effects are especially relevant for understanding how freshwater experience affects survival in anadromous fishes. Here, we study the carryover effects of juvenile salmon passage through a hydropower system (Snake and Columbia rivers, northwestern United States). To reduce the direct effect of hydrosystem passage on juveniles, some fishes are transported through the hydrosystem in barges, while the others are allowed to migrate in‐river. Although hydrosystem survival of transported fishes is greater than that of their run‐of‐river counterparts, their relative juvenile‐to‐adult survival (hereafter survival) can be less. We tested for carryover effects using generalized linear mixed effects models of survival with over 1 million tagged Chinook salmon, Oncorhynchus tshawytscha (Walbaum) (Salmonidae), migrating in 1999–2013. Carryover effects were identified with rear‐type (wild vs. hatchery), passage‐type (run‐of‐river vs. transported), and freshwater and marine covariates. Importantly, the Pacific Decadal Oscillation (PDO) index characterizing cool/warm (i.e., productive/nonproductive) ocean phases had a strong influence on the relative survival of rear‐ and passage‐types. Specifically, transportation benefited wild Chinook salmon more in cool PDO years, while hatchery counterparts benefited more in warm PDO years. Transportation was detrimental for wild Chinook salmon migrating early in the season, but beneficial for later season migrants. Hatchery counterparts benefited from transportation throughout the season. Altogether, wild fish could benefit from transportation approximately 2 weeks earlier during cool PDO years, with still a benefit to hatchery counterparts. Furthermore, we found some support for hypotheses related to higher survival with increased river flow, high predation in the estuary and plume areas, and faster migration and development‐related increased survival with temperature. Thus, pre‐ and within‐season information on local‐ and broad‐scale conditions across habitats can be useful for planning and implementing real‐time conservation programs.