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Cool‐water habitats provide increasingly vital refuges for cold‐water fish living on the margins of their historical ranges; consequently, efforts to enhance or create cool‐water habitat are becoming a major focus of river restoration practices. However, the effectiveness of restoration projects for providing thermal refuge and creating diverse temperature regimes at the watershed scale remains unclear. In the Klamath River in northern California, the Karuk Tribe Fisheries Program, the Mid‐Klamath Watershed Council, and the U.S. Forest Service constructed a series of off‐channel ponds that recreate floodplain habitat and support juvenile coho salmon (Oncorhynchus kisutch) and steelhead (O. mykiss) along the Klamath River and its tributaries. We instrumented these ponds and applied multivariate autoregressive time series models of fine‐scale temperature data from ponds, tributaries, and the mainstem Klamath River to assess how off‐channel ponds contributed to thermal regime diversity and thermal refuge habitat in the Klamath riverscape. Our analysis demonstrated that ponds provide diverse thermal habitats that are significantly cooler than creek or mainstem river habitats, even during severe drought. Wavelet analysis of long‐term (10 years) temperature data indicated that thermal buffering (i.e. dampening of diel variation) increased over time but was disrupted by drought conditions in 2021. Our analysis demonstrates that in certain situations, human‐made off‐channel ponds can increase thermal diversity in modified riverscapes even during drought conditions, potentially benefiting floodplain‐dependent cold‐water species. Restoration actions that create and maintain thermal regime diversity and thermal refuges will become an essential tool to conserve biodiversity in climate‐sensitive watersheds. [ABSTRACT FROM AUTHOR]

Objective: This study compares the probability of detecting juvenile Coho Salmon Oncorhynchus kisutch using both environmental DNA (eDNA) techniques and underwater visual count (UVC) surveys in northern California rivers. Here, UVC surveys commonly have detection probabilities (p) surpassing 0.90, providing an ideal setting to examine the performance of newer eDNA methods. We also evaluate the potential for using eDNA concentrations to predict the count of Coho Salmon within pool habitats. Methods: We conducted paired eDNA and UVC surveys in 96 pools across 25 stream reaches within the Smith River basin, California. Method-specific p and the effect of environmental covariates were estimated using multiscale occupancy modeling. We used generalized linear models to evaluate the relationship of fish counts to eDNA concentrations and habitat covariates. Result: The eDNA and UVC methods showed a high degree of agreement in detecting the presence of Coho Salmon within a pool (93% agreement) and survey reach (80% agreement). Detection probabilities for eDNA (peDNA) and for UVC (pUVC) were similar and high at median levels of pool residual depth and contributing basin area (peDNA = 91%, pUVC = 89%). Contributing basin area (a proxy for discharge) had a strong, negative effect that was more pronounced for peDNA than for pUVC (e.g., in the largest basins, peDNA = 34% whereas pUVC = 77%). We did not find eDNA concentrations to be a good predictor of Coho Salmon counts in small pools. Conclusion: This study demonstrates that eDNA methods yielded nearly identical results to UVC surveys in catchments <36 km2 and can provide a highly effective approach for determining the distribution of Coho Salmon. However, additional investigation is required before eDNA could be used to estimate relative abundance in small pools. [ABSTRACT FROM AUTHOR]

Along the northeast Pacific coast, the salmon-eating southern resident killer whale population (SRKW, Orcinus orca) have been at very low levels since the 1970s. Previous research have suggested that reduction in food availability, especially of Chinook salmon (Oncorhynchus tshawytscha), could be the main limiting factor for the SRKW population. Using the ecosystem modelling platform Ecopath with Ecosim (EwE), this study evaluated if the decline of the Pacific salmon populations between 1979 and 2020 may have been impacted by a combination of factors, including marine mammal predation, fishing activities, and climatic patterns. We found that the total mortality of most Chinook salmon populations has been relatively stable for all mature returning fish despite strong reduction in fishing mortality since the 1990s. This mortality pattern was mainly driven by pinnipeds, with increases in predation between 1979 and 2020 mortality ranging by factors of 1.8 to 8.5 across the different Chinook salmon population groups. The predation mortality on fall-run Chinook salmon smolts originating from the Salish Sea increased 4.6 times from 1979 to 2020, whereas the predation mortality on coho salmon (Oncorhynchus kisutch) smolts increased by a factor of 7.3. The model also revealed that the north Pacific gyre oscillation (NPGO) was the most important large-scale climatic index affecting the stock productivity of Chinook salmon populations from California to northern British Columbia. Overall, the model provided evidence that multiple factors may have affected Chinook salmon populations between 1979 and 2020, and suggested that predation mortality by marine mammals could be an important driver of salmon population declines during that time. [ABSTRACT FROM AUTHOR]

Objective: In the western United States, juvenile salmon Oncorhynchus spp. and steelhead O. mykiss are especially vulnerable to streamflow depletion in the dry season. Releasing water from off‐channel storage into small streams is a novel restoration strategy to offset impacts from anthropogenic flow alteration on salmonid fishes. To date, no studies have evaluated the ecological effects of small‐scale flow augmentations. Here, we quantify the effects of one such augmentation project on habitat connectivity, water quality, invertebrate drift, and juvenile salmonid movement and survival. Methods: Our study took place in a northern California stream and included an unusually wet summer (2019) and a more typical dry summer (2020). We used categorical and time‐series analyses in a before–after, control–impact (BACI) design, along with capture–mark–recapture methods to evaluate the ecological impacts of a 13.9‐L/s flow augmentation. Result: We found that differences in ambient streamflows between the two years mediated the physical and ecological effects of the flow augmentation treatment. In the dry year, habitat connectivity and dissolved oxygen markedly increased at sites over 1.5 km downstream from the point of augmentation, whereas during the wet year, the effects on those variables were negligible. In both years, invertebrate drift marginally increased after augmentation. Interpool movement of wild juvenile steelhead and stocked Coho Salmon O. kisutch increased after augmentation during the dry summer but not during the wet summer. Flow augmentation increased the survival probability for salmonids, with a larger effect during the dry summer (24% higher survival for Coho Salmon and 20% higher survival for steelhead) than during the wet summer (no effect was observed for steelhead survival, and Coho Salmon survival increased by 11%). Conclusion: This study indicates that appropriately designed small‐scale flow augmentations can improve conditions for rearing salmonids in small streams, particularly during dry years. More broadly, it provides empirical evidence that efforts to restore summer streamflow in small, salmon‐bearing streams can yield significant ecological benefits. Impact statementThere is growing interest in using novel approaches to offset human‐caused impacts on freshwater ecosystems. One approach involves releasing water from off‐channel storage directly into small, flow‐impaired streams to benefit endangered fishes—especially during the driest times of the year. This study explores how one of these "flow augmentation" projects affects the habitat, prey, and survival of threatened salmon and steelhead in a small coastal California stream. [ABSTRACT FROM AUTHOR]

Prolonged migration windows buffer migratory animal populations against uncertainty in resource availability. Understanding how intensifying droughts from climate change influence the migration window is critical for biodiversity conservation in a warming world. We explored how drought affects the seaward migration of endangered coho salmon (Oncorhynchus kisutch) near the southern extent of their range in California, USA. We tracked stream departures of juvenile coho, measuring streamflow and temperature in seven streams over 13 years, spanning a historic drought with extreme dry and warm conditions. Linear mixed effects models indicate that, over the range of observations, a decrease in seasonal streamflow (from 4.5 to 0.5 mm/day seasonal runoff) contracted the migration window by 31% (from 11 to 7 weeks). An increase from 10.2 to 12.8°C in mean seasonal water temperature hastened the migration window by three weeks. Pacific salmon have evolved to synchronize ocean arrival with productive ocean upwelling. However, earlier and shorter migration windows during drought could lead to mismatches, decreasing fitness and population stability. Our study demonstrates that drought‐induced low flows and warming threaten coho salmon in California and suggests that environmental flow protections will be needed to support the seaward migration of Pacific salmon in a changing climate. [ABSTRACT FROM AUTHOR]

Pacific salmon (Oncorhynchus spp.) are important to the ecology, economy, and cultures of the Pacific Northwest. Many populations of Pacific salmon in the Pacific Northwest are declining because of poor marine survival. We evaluated the role of Steller (Eumetopias jubatus) and California (Zalophus californianus) sea lions as predators of Pacific salmon. Roughly, half of the 1330 metric tons (t) of Pacific salmon eaten by Steller sea lions per year and of the 1220 t of Pacific salmon eaten by California sea lions per year in northwest Washington during 2010-2013 were coho salmon (O. kisutch). The response of Steller and California sea lions to the large run of pink salmon (O. gorbuscha) in 2011 was less than expected. Sea lions of these species rarely ate large (roughly ≥50 cm in total length) Chinook salmon (O. tshawytscha), indicating that they have limited direct competition for prey with the southern resident distinct population segment of killer whales (Orcinus orca). Combined, California and Steller sea lions in northwest Washington consumed a mass of coho salmon similar to that landed by commercial fisheries in Washington State. More work on modeling the effect of the predation by California and Steller sea lions on salmon populations, particularly for coho salmon, is needed to better evaluate the conservation and productivity of Pacific salmon. [ABSTRACT FROM AUTHOR]

Genetic diversity underpins species conservation and management goals, and ultimately determines a species' ability to adapt. Using freshwater environmental DNA (eDNA) samples, we examined mitochondrial genetic diversity using multigene metabarcode sequence data from four Oncorhynchus species across 16 sites in Oregon and northern California. Our multigene metabarcode panel included targets commonly used in population genetic NADH dehydrogenase 2 (ND2), phylogenetic cytochrome c oxidase subunit 1 (COI) and eDNA (12S ribosomal DNA) screening. The ND2 locus showed the greatest within‐species haplotype diversity for all species, followed by COI and then 12S rDNA for all species except Oncorhynchus kisutch. Sequences recovered for O. clarkii clarkii were either identical to, or one mutation different from, previously characterized haplotypes (95.3% and 4.5% of reads, respectively). The greatest diversity in O. c. clarkii was among coastal watersheds, and subsets of this diversity were shared with fish in inland watersheds. However, coastal streams and the Umpqua River watershed appear to harbour unique haplotypes. Sequences from O. mykiss revealed a disjunction between the Willamette watershed and southern watersheds suggesting divergent histories. We also identified similarities between populations in the northern Deschutes and southern Klamath watersheds, consistent with previously hypothesized connections between the two via inland basins. Oncorhynchus kisutch was only identified in coastal streams and the Klamath River watershed, with most diversity concentrated in the coastal Coquille watershed. Oncorhynchus tshawytscha was only observed at one site, but contained multiple haplotypes at each locus. The characterization of genetic diversity at multiple loci expands the knowledge gained from eDNA sampling and provides crucial information for conservation actions and genetic management. [ABSTRACT FROM AUTHOR]

Recent droughts raise global concern over potential biodiversity loss and mitigating impacts to vulnerable species has become a management priority. However, drought impacts on populations are difficult to predict, in part, because habitat refuges can buffer organisms from harsh environmental conditions. In a global change context, more extreme droughts may turn previously suitable habitats into ecological traps, where vulnerable species can no longer persist. Here, we explore the impacts of California's recent record‐breaking drought on endangered juvenile Coho salmon. We estimated the variability of cumulative salmon survival using mark–recapture of nearly 20,000 tagged fish in intermittent stream pools during a 7‐year period encompassing drought and non‐drought conditions. We then determined the relative importance of physical habitat, streamflow, precipitation, landscape, and biological characteristics that may limit survival during drought. Our most striking result was an increase in the number of pools with reduced or zero survival during drought years and a coincident increase in spatial variability in survival among study reaches. In nearly half of the stream pools, salmon survival during drought was similar to mean survival of pools assessed during non‐drought years, indicating some pools had remarkable resistance (ability to withstand disturbance) to extreme drought. Lower survival was most attributable to longer duration of disconnection between upstream and downstream habitats, a consequence of increasing drought severity. Our results not only suggest that many pools sustain juvenile salmon in non‐drought years transition into ecological traps during drought but also highlight that some pools serve as refuges even under extreme drought conditions. Projected increases in drought severity that lead to longer droughts and greater habitat fragmentation could transform an increasing proportion of suitable habitats into ecological traps. Predicting future impacts of drought on Coho salmon and other sensitive species will require identification and protection of drought refuges and management strategies that prevent further habitat fragmentation. [ABSTRACT FROM AUTHOR]

Like many rivers and streams in forests of the Pacific Northwest, California north coast rivers and streams have been depleted of downed wood through timber harvest and direct wood removal. Due to the important role of wood in creating and maintaining salmonid habitat, wood augmentation has become a common element of stream restoration. Restoration efforts in North America often focus on building anchored, engineered wood structures at the site scale; however, these projects can fail to meet restoration goals at the watershed scale, do not closely mimic natural wood loading processes or dynamics, and can be expensive to implement. For critically imperiled populations of Coho SalmonOncorhynchus kisutchin California, there is a strong impetus to achieve as much habitat restoration as possible in priority watersheds in the shortest time and with limited resources, so cost-efficient techniques are necessary. In this multi-site project, we investigated unanchored techniques for wood loading to evaluate cost and contribution to salmonid habitat in Mendocino County, California. Over a period of 6 years, 72.4 km of stream were treated with 1,973 pieces of strategically placed wood. We found that unanchored wood loading techniques were much less costly than commonly used anchored techniques, reliably improved habitat, and retained wood at high rates (mean = 92%) in small- to moderate-sized streams, at least over the short term (<6 years). The average cost of design and construction for the unanchored projects was US$259 per log, equivalent to 22% of the cost associated with the anchored wood augmentation methods examined here. Our results suggest that this unanchored wood loading approach has the potential to increase the pace and scale at which wood augmentation projects are implemented in the Pacific Northwest and beyond. Received January 22, 2014; accepted June 25, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT Elevated stream temperature is a primary factor limiting the coho salmon ( Oncorhynchus kisutch) population in California's Shasta River Basin. Understanding the mechanisms driving spatial and temporal trends in water temperature throughout the Shasta River is critical to prioritising river restoration efforts aimed at protecting this threatened species. During the summer, the majority of streamflow in the Shasta River comes from large-volume, cold-water springs at the head of the tributary Big Springs Creek. In this study, we evaluated the initial character of this spring water, as well as the downstream fate and transport of these groundwater inflows during July and August 2008. Our results indicated that Big Springs Creek paradoxically provided both cool and warm waters to the Shasta River. During this period, cool groundwater inflows heated rapidly in the downstream direction in response to thermal loads from incoming solar radiation. During the night time, groundwater inflows did not appreciably heat in transit through Big Springs Creek. These diurnally varying water temperature conditions were inherited by the Shasta River, producing longitudinal temperature patterns that were out of phase with ambient meteorological conditions up to 23 km downstream. Findings from this study suggest that large, constant temperature spring sources and spring-fed rivers impart unique stream temperature patterns on downstream river reaches that can determine reach-scale habitat suitability for cold-water fishes such as coho salmon. Recognising and quantifying the spatiotemporal patterns of water temperature downstream from large spring inflows can help identify and prioritize river restoration actions in locations where temperature patterns will allow rearing of cold-water fishes. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Coho salmon ( Oncorhynchus kisutch) of the Southern Oregon/Northern California Coast (SONCC) Evolutionarily Significant Unit (ESU) is federally listed as a threatened species. The Trinity River Restoration Program (TRRP) is rehabilitating the Trinity River to restore coho salmon (coho) and other salmonid populations. In order to evaluate the program's actions, several studies of movements and behavior of coho in the Trinity River were conducted from 2006 to 2009, including snorkel surveys and mark-recapture techniques based on Passive Integrated Transponder (PIT) tags, elastomer tags, and radio transmitters. Catch, recapture, and condition of natural sub-yearlings, along with site fidelity and emigration of hatchery-reared yearlings in rehabilitated and reference habitats, were studied. Location was important because coho were absent from the lower controlled and rehabilitated sites most of the time. However, rehabilitation did not have a significant effect on natural coho salmon at the site level. Apparent survival of radio-tagged, hatchery-reared yearling coho released downstream from Lewiston Dam was much lower in the first 10 km downstream from the release site than in other areas between Lewiston Dam and the Klamath River estuary. Estimated survival of yearling hatchery coho salmon per 100 km down to Blake's Riffle was estimated at 64 % over the distance of the 239 km study area. Migration primarily occurred at night in the upper Trinity River; however, as yearlings moved through the lower Trinity River towards the Klamath River, estuary nocturnal migration became less. Apparent survival was generally lowest in areas upstream from the North Fork of the Trinity River. [ABSTRACT FROM AUTHOR]

We monitored the movement of coho salmon ( Oncorhynchus kisutch) smolts with acoustic transmitters from freshwater, through the freshwater/estuary ecotone, through the estuary, and to ocean entry to determine residence time and habitat use in Humboldt Bay, California. Tagged fish were monitored with a fixed receiver network and mobile tracking conducted from a boat. Coho salmon observed during the two-year study resided in Humboldt Bay beginning at least as early as late April and resided through the beginning of July. Coho salmon smolts spent more time in the freshwater/estuary ecotone compared to the lower estuary and spent an average of 10-12 days migrating to Humboldt Bay. Coho salmon smolts resided in Humboldt Bay, a marine embayment, for an average of 15-22 days prior to leaving the bay for the open ocean. Coho salmon smolts, as observed from mobile tracking, used deep channels and channel margins more often than floating eelgrass mats, pilings, and docks. In addition, tagged fish were more often detected in the central portions of Humboldt Bay characterized by deep channels with narrow intertidal margins. There were fewer detections in other portions of the bay characterized by shallow channels with large intertidal mudflats and eelgrass meadows. Relatively short transmitter life (70 days) precluded determining the latest date of coho salmon smolt residency in Humboldt Bay. In addition, tag size limited use to the largest emigrating smolts and may not represent the behaviors of the smaller-sized smolts which were more abundant. [ABSTRACT FROM AUTHOR]

Coho salmon Oncorhynchus kisutch are a threatened species in California. In the Shasta River, they may be caught in an ecological trap that is exacerbating their decline. Adults appear to have equal preferences for spawning habitat that reduces the survival of their young and that of apparently similar quality where survival would be more likely. The primary cause of juvenile mortality is water withdrawals, which degrade summer water quality and create barriers to movement to habitats with more suitable rearing conditions. The situation has been exacerbated by the addition of gravel to support spawning fall-run Chinook salmon O. tshawytscha, creating habitat that is also attractive to spawning coho salmon in locations where juvenile coho salmon survival will be extremely low. The Shasta River acts as a conceptual model of how habitat degradation and ecologically naive restoration actions may combine to create severe ecological traps for nontarget species. Received March 10, 2011; accepted October 11, 2011 [ABSTRACT FROM AUTHOR]

We examined the incidental catches of American shad (Alosa sapidissima) taken during research cruises and in commercial and recreational landings along the Pacific coast of North America during over 30 years of sampling. Shad, an introduced species, was mainly found over the shallow continental shelf, and largest catches and highest frequency of occurrences were found north of central Oregon, along the coasts of Washington and Vancouver Island, and in California around San Francisco Bay. Migrations to the north off Washington and Vancouver were seen during spring to fall, but we found no evidence for large-scale seasonal migrations to the south during the fall or winter. The average weight of shad increased in deeper water. Sizes were also larger in early years of the study. Most were caught over a wide range of sea surface temperatures (11-17°C) and bottom temperatures (6.4-8.0°C). Abundance of shad on the continental shelf north of 44°N was highly correlated with counts of shad at Bonneville Dam on the Columbia River in the same year. Counts were negatively related to average weights and also negatively correlated with the survival of hatchery coho salmon (Oncorhynchus kisutch), indicating that survival of shad is favored by warm ocean conditions. Examining the catch during research cruises and commercial and recreational landings, we concluded that American shad along the Pacific coast have adapted to the prevailing environmental conditions and undertake only moderate seasonal migrations compared with the long seasonal migrations of shad along the Atlantic coast of North America. We suggest that the large spawning populations in the Columbia River and San Francisco Bay areas explain most of the distributional features along the Pacific coast. [ABSTRACT FROM AUTHOR]

Yearling juvenile coho and Chinook salmon were sampled on 28 cruises in June and September 1981-85 and 1998-07 in continental shelf and oceanic waters off the Pacific Northwest. Oceanographic variables measured included temperature, salinity, water depth, and chlorophyll concentration (all cruises) and copepod biomass during the cruises from 1998-07. Juvenile salmonids were found almost exclusively in continental shelf waters, and showed a patchy distribution: half were collected in ∼5% of the collections and none were collected in ∼40% of the collections. Variance-to-mean ratios of the catches were high, also indicating patchy spatial distributions for both species. The salmon were most abundant in the vicinity of the Columbia River and the Washington coast in June; by September, both were less abundant, although still found mainly off Washington. In June, the geographic center-of-mass of the distribution for each species was located off Grays Harbor, WA, near the northern end of our sampling grid, but in September, it shifted southward and inshore. Coho salmon ranged further offshore than Chinook salmon: in June, the average median depth where they were caught was 85.6 and 55.0 m, respectively, and in September it was 65.5 and 43.7 m, respectively. Abundances of both species were significantly correlated with water depth (negatively), chlorophyll (positively) and copepod biomass (positively). Abundances of yearling Chinook salmon, but not of yearling coho salmon, were correlated with temperature (negatively). We discuss the potential role of coastal upwelling, submarine canyons and krill in determining the spatial distributions of the salmon. [ABSTRACT FROM AUTHOR]

The article presents a study which discusses the use of surface water balance model to assess the effect of small water projects on stream flow in the Russian River basin in northern coastal California. It notes that the growing water needs of human has caused an increase small water project. The model was adapted to examine the impact of small instream diversion on the catchment discharge and its ecological effects. The evaluations were used to identify the possible effects of the projects on anadromous salmonids such as coho salmon Oncorhynchus kisutch. Results show the significant threat posed by direct instream diversion to aquatic ecosystem. It suggests the efficient use of surface water balance in examining the impact of decentralized water project on catchment stream flow.

We assessed the relative importance of various factors contributing to spawning site use by a population of threatened coho salmon Oncorhynchus kisutch in Freshwater Creek, California, and created a predictive model of spawning habitat selection based on logistic regression analysis. We excluded sampling sites that previous studies had established as unsuitable on the basis of depth and substrate criteria and asked why fish chose particular locations and not others in seemingly suitable habitat. We evaluated surface water velocity, depth, substrate size composition, gravel inflow rates, vertical hydraulic gradient, geomorphic channel units, hyporheic water physicochemistry, cover, and proximity to other redds not in sampling sites during the 2004-2005 spawning season. In univariate comparisons with unused sites, coho salmon selected sites with a smaller median particle diameter, a larger percentage of gravel-pebble substrate, and higher gravel inflow rates. Based on multivariate logistic regression, the probability of a site's being used for spawning was best modeled as a positive function of the gravel-pebble fraction of the substrate, location at a pool or run tail, and the presence of existing redds in close proximity to the site. This model explained 38% of the variation in the data and was a better predictor of spawning habitat use than a more traditional model based on depth, velocity, and substrate. Our results highlight the potential importance of social behavior in contributing to habitat selection by spawning salmonids. [ABSTRACT FROM AUTHOR]

The feeding habits of juvenile coho salmon, Oncorhynchus kisutch, in the northern California Current were examined using samples from two different time periods (1980–85 and 1998–2003) of highly contrasting oceanographic conditions. The goal was to test the influence of interannual and interdecadal changes in taxonomic composition of prey, feeding intensity, and size spectra of teleost prey. Analyses were done for samples taken both early in the summer (June) shortly after the salmon enter the ocean, and also in late summer (September) following some ocean residency. Fish prey dominated coho salmon diets by weight during most years, but this trend was more pronounced during the 1980–85 sampling period. In terms of numerical composition, the diets were more variable on an interannual basis, but decapod larvae and euphausiids were important prey in most years. Pteropods and copepods were important prey during weak upwelling or El Niño years, whereas euphausiids were important during strong upwelling or otherwise highly productive years. Hyperiid amphipods comprised a substantial proportion of the diets only in 2000. Coho salmon showed highly significant differences in prey composition among years or between decades both in weight and numerical composition. The percentage of empty stomachs was highly variable by year in both June and September, but was significantly different only for September between decades. In contrast, an index of feeding intensity did not show many significant changes in either comparison. However, the relative size ratios for fish prey consumed were highly variable by year, and larger than average fish prey were consumed during 1998, leading to the highest feeding intensity observed. [ABSTRACT FROM AUTHOR]

Kaczynski and Alvarado (2006) have challenged the established southern boundary of coho salmon (Oncorhynchus kisutch) at the San Lorenzo River. They conclude that it is improbable coho salmon maintained self-sustaining populations south of San Francisco Bay, based primarily on evidence from early museum collections and literature, the archaeological record, analyses of ocean conditions, and suitability of habitat. They suggest that hatchery plantings were the source of these coho salmon south of San Francisco Bay. Using the same and new information, we are able to counter these statements. Our examination of existing records found no reason to discount the coho salmon collections made in 1895 from streams south of San Francisco. Early distributional records state that coho salmon were abundant from San Francisco northward, but did not indicate coho salmon were absent south of San Francisco. Recent archeological evidence documents the presence of coho salmon in middens south of San Francisco prior to European habitation of the region. Furthermore, we found no creditable climatic, oceanographic, or ecological evidence for habitat differences between areas immediately north and south of San Francisco Bay. In fact, we believe that there is a more reasonable habitat and faunal break south of the San Lorenzo River, encompassing the allegedly controversial southern range of the coho salmon. [ABSTRACT FROM AUTHOR]

California coho salmon (Oncorhynchus kisutch) are under legal protection owing to significant declines in abundance over the last decades. Previously, California coho salmon were characterized as having low genetic diversity and weak population subdivision, attributable potentially to homogenization by out-of-basin hatchery releases. Here, diversity at seven highly polymorphic microsatellite DNA markers is assessed within and among 32 collections of coho salmon from 16 California watersheds. In 71% of local populations, genotypic composition deviates significantly from that expected under the assumption of random mating. We develop and apply methods to adjust for two potential causes of deviation from random mating expectations: (i) Wahlund effects, owing to heterogeneous collections of individuals, and (ii) the "Allendorf–Phelp's effect", owing to closely related juveniles in samples. Such population-level "adjustments" reduce within-region and increase among-region variance; after adjustment, we find strong concordance of genetic and geographic distances. We conclude that stock transfers have had minimal impact on population structure and that California coho salmon populations likely comprise small numbers of endemic breeders, potentially experiencing high levels of genetic drift and inbreeding. [ABSTRACT FROM AUTHOR]

Pacific salmon species including the U.S. federally endangered coho salmon (Oncorhynchus kisutch) and the U.S. federally threatened steelhead trout (Oncorhynchus mykiss) have declined at an alarming rate in the last 40 years. Two of the main causes for the decline in coastal coho populations include increases in temperature and contaminant loads in coastal watersheds. Zinc, in particular, is one of the most common contaminants in aquatic systems. Using an experimental mesocosm design, we examined physiological, biochemical, and behavioral responses of coho salmon to excess dietary zinc and increased temperatures, with the ultimate goal of relating results to wild populations of coho salmon and steelhead in the Navarro River, California. Fish were obtained from a hatchery and divided into four treatments: low water temperature-no dietary zinc, high temperature-no zinc, low temperature-zinc, and high temperature-zinc. Each treatment had four replicate tanks. Zinc concentrations in liver increased during exposure to a high zinc diet. Iron concentrations in liver increased during simultaneous exposure to high zinc diet and increased temperature, and growth was reduced in this experimental treatment. Expression of hsp-70 was not significantly different between treatments, but showed decreasing trends with high dietary zinc and high temperature. Feeding rate increased with exposure to a high zinc diet. Comparison with steelhead trout samples from the Navarro River, California, showed levels of zinc, iron, and hsp-70 greater than those found in the experimental Coho salmon. All comparisons between the hatchery coho salmon and wild steelhead should be viewed with caution due to the differences between species, the laboratory and natural environment, and the genetic differences between wild and hatchery fish. [ABSTRACT FROM AUTHOR]

We used the average fork length of age-3 returning coho ( Oncorhynchus kisutch) and age-3 ocean-type and age-4 stream-type Chinook ( Oncorhynchus tshawytscha) salmon along the northeast Pacific coast to assess the covariability between established oceanic environmental indices and growth. These indices included the Multivariate El Niño-Southern Oscillation Index (MEI), Pacific Decadal Oscillation (PDO), Northern Oscillation Index, and Aleutian Low Pressure Index. Washington, Oregon, and California (WOC) salmon sizes were negatively correlated with the MEI values indicating that ultimate fish size was affected negatively by El Niño-like events. Further, we show that the growth trajectory of WOC salmon was set following the first ocean winter. Returning ocean-type British Columbia-Puget Sound Chinook salmon average fork length was positively correlated with the MEI values during the summer and autumn of return year, which was possibly a result of a shallower mixed layer and improved food-web productivity of subarctic Pacific waters. Size variation of coho salmon stocks south of Alaska was synchronous and negatively correlated with warm conditions (positive PDO) and weak North Pacific high pressure during ocean residence. [ABSTRACT FROM AUTHOR]

We investigated whether sand seals form in the upper egg pocket of salmonid redds and improve egg survival in a sediment-impacted coastal stream in northern California. Sand seals can potentially reduce infiltration of detrimental finer sand and silt into the lower egg pocket. We predicted sand seals would form when the redds were exposed to streamflows high enough to entrain coarse sand and form seals. Using artificial redds of coho salmon Oncorhynchus kisutch, we conducted sediment analyses of the upper and lower egg pockets and found that protective sand seals formed in redds when discharge was two or more times the flow that entrains the median particle size of the streambed. When the coarse sand in the upper egg pocket was incorporated into a two-stage model that predicted survival to hatching and emergence, it greatly improved predictions in years with higher flows in both natural and artificial redds. However, the sand seals provided little protection when suspended sediment flux was high from logging or road construction. We built the model used for these predictions with data from artificial redds and applied it to natural redds during 6 years of different flow regimes. Predictor variables included cumulative flow above the entrainment flow, peak discharge, coarse sand in the upper egg pocket, fine sediment in riffle gravel, coarse sand in the upper and entire egg pocket, suspended sediment flux, and presence of predaceous worms. The model explained 67% of the variance in egg survival to emergence in coho salmon natural redds. We suggest that managers consider the complex interactions of streamflow, sediment transport, formation of sand seals, and fine-sediment infiltration when estimating salmonid reproductive success in sediment-impacted streams. [ABSTRACT FROM AUTHOR]

Hatchery and wild juvenile populations of steelheadOncorhynchus mykissand coho salmonOncorhynchus kisutch, in a small coastal watershed in central California, were sampled throughout the year in a stream and at a hatchery. Both species grew faster in captivity than in the wild. Hatchery fish of both species had elevated gill Na+, K+-ATPase activity, and thus were ready to enter sea water when planted during the wild fish migration. Downstream migrant trapping and stream surveys indicated that hatchery smolts went to sea soon after planting, consequently avoiding the effects of competition and predation that commonly occur when hatchery-bred juveniles are released. Adult steelhead were also sampled throughout the watershed. The return of hatchery steelhead was highly synchronized with that of wild steelhead, indicating that hatchery propagation had no adverse effects on the timing of the run. A disproportionate number of hatchery steelhead returned to the tributary where the hatchery was located, despite being planted throughout the watershed. Hatchery steelhead did not differ in mean age or size from wild steelhead. Observations of spawning indicated that hatchery and wild steelhead interbreed. Competition for mates or spawning substratum was rarely observed between hatchery and wild steelhead. Many of the problems commonly associated with artificial propagation can be avoided in small coastal watersheds when wild broodstock are used and fish are released as smolts. [ABSTRACT FROM AUTHOR]

• Examining correlations among indices helps to detect climate forcing factors. • Studied 43 freshwater, marine and climate indices; 72 sites in western USA. • Correlations among indices clustered by NW/SW regions and index types. • Correlations across short periods (10-year windows) often change over time. • Multiple climate indices switching phases together strengthen correlations. The common practice of incorporating environmental indices into population models has greatly advanced our understanding of ecological systems. Unfortunately, we are increasingly seeing published correlations between population indicators and environmental indices breaking down when tested with new data. Examining how the correlations among indices change over time could help explain underlying causal mechanisms, which ultimately strengthen the basis for prediction of population indicators. For migratory animals such as anadromous salmon (Oncorhynchus spp.), the habitat conditions they experience can affect their lifetime fitness and population viability. We analyzed 43 freshwater, marine, and climate indices associated with 72 river sites and five coastal ecoregions inhabited by Chinook and coho salmon (O. tshawytscha and O. kisutch) in the western USA. Utilizing long time series (ranging from 32 to 124 years), we examined spatial and temporal patterns in correlations through hierarchical clustering across sites and non-stationarity across time. Individual river sites clustered into two Northwest and one Southwest groups. Northwest sites generally showed stronger correlations between freshwater and climate indices, while Southwest sites showed stronger correlations within freshwater or within marine/climate indices. For a closer examination at shorter periods, we parsed the time series into 10-year windows and showed how pairwise correlations changed over time with spring–summer Pacific Decadal Oscillation index in the Northwest and with spring flow in the Southwest. Stronger correlations across multiple indices tended to occur when large-scale climatic events (e.g., Oceanic Niño and Pacific Decadal Oscillation indices) were in-phase, and phase transitions (e.g., from positive to negative) occurred in the same 10-year window. In a third analysis, we assessed how well indices provided unique vs. confounding/complex information and had consistent vs. varying relationships based on the mean and variance of 10-year correlations. Across index types, the variance in correlations tended to be lowest in marine vs. climate indices, higher among freshwater indices, and highest for freshwater vs. marine/climate indices. Yet, the mean strength of correlations for freshwater vs. marine/climate indices was still comparable to those among freshwater ones. Overall, identifying time periods when correlations tend to change will help interpret historical and projected population indicators. Spatial trends in the strength of correlations also indicate that the level of confounding effects among indices can differ regionally. We emphasize the importance of knowing the strength and variability of correlations among indices, and their representativeness of ecological processes in the context of combined phases of multiple climatic indices. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the predation of American bullfrogs on juvenile coho salmon in Humboldt County, California. It shows that a juvenile coho salmon was found on the stomach of a captured adult female bullfrog when it was dissected. It is believed that the juvenile coho salmon was from a trap that were used to capture migrating salmonid smolts in Freshwater Creek in Humboldt Bay, Humboldt County, California. The researchers highly suggest the implementation of local ecological requirements to limit the interaction between juvenile coho salmon and bullfrogs.

The myxozoan parasite Ceratonova shasta is an important pathogen that infects multiple species of Pacific salmonids. Ongoing genetic surveillance has revealed stable host-parasite relationships throughout the parasite's endemic range. We applied Bayesian phylogenetics to test specific hypotheses about the evolution of these host-parasite relationships within the well-studied Klamath River watershed in Oregon and California, USA. The results provide statistical support that different genotypes of C. shasta are distinct lineages of one species, which is related to two other Ceratonova species in the same ecosystems; Ceratonova X in speckled dace and C. gasterostea in threespine stickleback. Furthermore, we found strong support for the hypothesis that C. shasta type 0 in native steelhead trout and type I in Chinook salmon each evolved with a specialist host adaptation strategy, while C. shasta type II in coho salmon resulted from a generalist host adaptation strategy. Inferred date and host species of the most recent common ancestor of extant Klamath basin types indicate that it occurred between 14,000 and 21,000 years ago, and most likely infected a native steelhead or rainbow trout host. • Field-observed differences are revealed to be two distinct evolutionary adaptation strategies that are supported by statistically significant population genetic analyses. • The most recent common ancestor of extant types occurred between 14,000–21,000 years ago, infecting a native steelhead or rainbow trout host. [ABSTRACT FROM AUTHOR]

The article discusses the endangered status of coho salmon that occupy the Lagunitas Creek on the central California coast. The coho is thought to be on the brink of extinction as reflected by the institution of a species survival plan by the U.S. National Marine Fisheries Service (NMFS). Factors that may contribute to the declining coho population are noted including fresh-water impacts brought on by dams, mining, agriculture, and urbanization. NMFS geneticist John Carlos Garza is cited regarding the prospective use of coho hatcheries.

This article presents information about the efforts of conservationist Al Pisciotta for the survival of coho salmon fishes in California. The Lagunitas Creek Watershed, located just outside California's Point Reyes National Seashore, is home to 10-20% of all wild coho salmon in the state. It is the largest single population of salmon in California. Pisciotta, whose day job involves setting up conventions in San Francisco, works as a volunteer rescuer for the fish. Last summer, he saved 1400 tiny fishes. Pisciotta is also a member of the group Salmon Protection and Watershed Network (SPAWN). For the members of this group, the global biodiversity crisis has become a very up-close and personal issue. The group was founded in 1996 by Todd Steiner, a biologist who also works as the head of the Sea Turtle Restoration Project. SPAWN has had some successes. The group includes schoolchildren, software industry workers, and even one group of accountants. It counts a total of 14000 salmon and trout saved during Fish Rescue Days over the past 6 years.