Landscape ecotoxicology of coho salmon spawner mortality in urban streams

In the Pacific Northwest of the United States, adult coho salmon (Oncorhynchus kisutch) returning from the ocean to spawn in urban basins of the Puget Sound region have been prematurely dying at high rates (up to 90% of the total runs) for more than a decade. The current weight of evidence indicates that coho deaths are caused by toxic chemical contaminants in land-based runoff to urban streams during the fall spawning season. Non-point source pollution in urban landscapes typically originates from discrete urban and residential land use activities. In the present study we conducted a series of spatial analyses to identify correlations between land use and land cover (roadways, impervious surfaces, forests, etc.) and the magnitude of coho mortality in six streams with different drainage basin characteristics. We found that spawner mortality was most closely and positively correlated with the relative proportion of local roads, impervious surfaces, and commercial property within a basin. These and other correlated variables were used to identify unmonitored basins in the greater Seattle metropolitan area where recurrent coho spawner die-offs may be likely. This predictive map indicates a substantial geographic area of vulnerability for the Puget Sound coho population segment, a species of concern under the U.S. Endangered Species Act. Our spatial risk representation has numerous applications for urban growth management, coho conservation, and basin restoration (e.g., avoiding the unintentional creation of ecological traps). Moreover, the approach and tools are transferable to areas supporting coho throughout western North America.     

Physiological responses of free-swimming adult coho salmon to simulated predator and fisheries encounters

The responses of free-swimming adult coho salmon (Oncorhynchus kisutch) to simulated predator and fisheries encounters were assessed by monitoring heart rate (f(H)) with implanted data loggers and periodically taking caudal blood samples. A 10- or 30-min corralling treatment was conducted to simulate conspecifics being cornered by a predator or corralled by fisheries gear without physical contact. Corralling rapidly doubled f(H) from ～31 beats min(-1) to a maximum of ～60 beats min(-1), regardless of the duration of the corralling. However, recovery of f(H) to precorralling levels was significantly faster after the 10-min corralling (7.6 h) than after the 30-min corralling (11.5 h). An exhaustive-exercise treatment (chasing for 3 min, with physical contact) to simulate a predator chasing a fish to exhaustion or a fish becoming exhausted after encountering fisheries gear resulted in increased f(H) (to 60 beats min(-1)), plasma lactate, glucose, sodium, osmolality, and cortisol (males only) and a significant decrease in mean corpuscular hemoglobin concentration. Recovery of f(H) and most blood variables was complete about 16 h after exhaustive exercise and handling. The results illustrate a clear relationship between the intensity of exercise and the duration required for recovery of f(H). Changes in f(H) were significantly correlated with those in plasma lactate, chloride, and sodium at 1 h after the exercise treatment protocols. Thus, measurements of f(H) may provide an accurate indication of the general physiological response of salmonids to exhaustive exercise in the natural environment.     

Embryo survival and smolt to adult survival in second‐generation outbred coho salmon

Outbreeding depression was not detectable in observations of embryonic survival and of survival of smolts to adulthood relative to controls in coho salmon Oncorhynchus kisutch experimentally outbred over two generations by crossing fish from three widely separated populations. Survival in outbred coho salmon was not detectably less than that in second‐generation hybrid controls or second‐generation parental controls. Variation of embryonic survival was affected by the maternal source population and by individual females but not by the paternal source population or by individual males. Survival of smolts to adulthood at sea was greater in one second‐generation control group than in two others, but survival in second‐generation outbred groups was no less than in parental controls or hybrid controls.     

Comparison of allopatric cutthroat trout stocks with those sympatric with coho salmon and sculpins in small streams

Synopsis Juvenile stocks of allopatric (upstream of barrier falls) cutthroat troutSalmo clarki and those sympatric (downstream of barrier falls) with coho salmonOncorhynchus kisutch and sculpinsCottus spp., were sampled during the late summer period of low flows in six small coastal streams in British Columbia. The objective was to obtain and compare information on pattern of habitat use and fish size distribution of these two trout types. In most instances, density (n m^–2; g m^–2) of cutthroat trout was considerably greater in pools and glides in the allopatric than in the sympatric stocks. The sympatric salmonids were dominated by juvenile coho salmon in pools and cutthroat trout in riffles. Sympatric cutthroat trout constituted from 7 to 45 % of the salmonids present in pools and from 50 to 90% in riffles. Glides were areas of intermediate densities for both salmonids, although coho salmon was the more abundant species in most instances. The density of sculpins was high in all three habitat types, and frequently it exceeded that of coho salmon and cutthroat trout combined. Sympatric cutthroat trout consisted primarily of underyearling fish, whereas allopatric cutthroat trout consisted primarily of two or more age classes with a large proportion of them living in pools. When tested in a laboratory stream both types of cutthroat trout had similar habitat preferences and agonistic behaviours, with the exception that allopatric trout made greater use of cover and defended pools more intensely than sympatric trout when the flow was increased. The results of this study provide insight of potential impact of coho salmon juvenile transplants into stream segments supporting allopatric cutthroat trout.     

Preferable summering habitat of returning adult masu salmon in the natal stream

The preferable summering habitat of returning adult masu salmon Oncorhynchus masou Brevoort was examined in 31 study pools of a small stream in northern Hokkaido, Japan. A total of 23 salmon were captured and were present in only 10 of the study pools. Female salmon were found to be significantly larger than male salmon. Habitat characteristics were expressed by six environmental variables: mean water depth, maximal cover size, mean current velocity, pool volume, substratum coarseness and cover area. There were no significant differences between the pools with salmon and those without salmon in terms of substratum coarseness and cover area. However, significant differences were found in mean water depth, maximal cover size, mean current velocity and pool volume. The analysis found that the pools with salmon were discriminated from those without salmon at a level of 93.5% which was determined by the six environmental variables. Our results revealed that the returning adult salmon selectively used the pools with greater depth, large cover and slow current velocity as their preferable summering habitat. The results also found that the summering habitat of salmon can be estimated by measuring only six environmental variables. Therefore, these variables can be considered useful parameters in determining the summering habitat components of returning adult masu salmon and can contribute to the conservation and restoration strategy of this species by providing a better understanding of the relationship between fish and their habitat.     

Microdistribution of macroinvertebrates in lowland streams

Summary Most benthic macroinvertebrate species are related to substrates types. Three main groups of species can be distinguished, each consisting of species with a similar preference for coarse mineral substrate (gravel), fine mineral substrate (sand) and organic material (leaves and/or coarse detritus), respectively. The particle size of the mineral component of the substrate, as well as the amount and the nature of the organic detritus, and the various combinations of both components, influence the microdistribution of most of the investigated species. Factors related to the substrate (e.g. oxygen and current conditions and food availability) are also important.     

Prevalence and analysis of Renibacterium salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha in North Puget Sound

Renibacterium salmoninarum causes bacterial kidney disease (BKD), a chronic and sometimes fatal disease of salmon and trout that could lower fitness in populations with high prevalences of infection. Prevalence of R. salmoninarum infection among juvenile Chinook salmon Oncorhynchus tshawytscha inhabiting neritic marine habitats in North Puget Sound, Washington, USA, was assessed in 2002 and 2003. Fish were collected by monthly surface trawl at 32 sites within 4 bays, and kidney infections were detected by a quantitative fluorescent antibody technique (qFAT). The sensitivity of the qFAT was within an order of magnitude of the quantitative real-time PCR (qPCR) sensitivity. Prevalence of infection was classified by fish origin (marked/hatchery vs. unmarked/likely natural spawn), month of capture, capture location and stock origin. The highest percentages of infected fish (63.5 to 63.8%) and the greatest infection severity were observed for fish collected in Bellingham Bay. The lowest percentages were found in Skagit Bay (11.4 to 13.5%); however, there was no difference in prevalence between marked and unmarked fish among the capture locations. The optimal logistic regression model of infection probabilities identified the capture location of Bellingham Bay as the strongest effect, and analysis of coded wire tagged (CWT) fish revealed that prevalence of infection was associated with the capture location and not with the originating stock. These results suggest that infections can occur during the early marine life stages of Chinook salmon that may be due to common reservoirs of infection or horizontal transmission among fish stocks.     

Pheromones and the water source preferences of adult coho salmon Oncorhynchus kisutch Walbaum

It has been proposed that population-specific pheromones released by juvenile salmonids guide the adults on their homing migration (Nordeng, 1977). To evaluate this hypothesis, adult coho salmon, Oncorhynchus kisutch , were tested in a two-choice apparatus with a variety of water sources. Coho salmon preferred home water without coho odours over an unfamiliar water source (city water). Adults preferred water conditioned by juveniles of their own population over plain city water, but did not prefer water conditioned by juveniles of their own population over that of another.     

Prevalence of larval Anisakis simplex in pen-reared and wild-caught salmon (Salmonidae) from Puget Sound, Washington

The abundance of parasites of public health significance in pen-reared salmon and wild-caught salmon was compared. Two hundred eighty-seven salmon from Puget Sound, Washington, were examined for third-stage larvae of Anisakis simplex. Of these fish, 237 Atlantic salmon (Salmo salar), coho salmon (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) were reared in commercial salmon pens and 50 sockeye salmon (O. nerka) were caught during their spawning migration. All wild-caught salmon were found to be infected with larval A. simplex; conversely, all pen-reared fishes lacked such infections. Edible musculature of wild salmon were infected with 581 (87%) nematode larvae. Of other salmon parasites known to infect humans, one Diphyllobothrium sp. plerocercoid was collected from each of three of the 50 wild-caught salmon. The study showed that farmed salmon may increase the margin of safety for consumers of raw seafood.     

Response of meiobenthos to migrating ripples in sandy lowland streams

Hydrobiologia - Stream sediments move at low flow forming migrating ripples. These ripples can cover substantial areas where benthic communities experience erosion-resting cycles of sand grains....     

Adaptive trade-offs in juvenile salmonid metabolism associated with habitat partitioning between coho salmon and steelhead trout in coastal streams

1. Adaptive trade-offs are fundamental to the evolution of diversity and the coexistence of similar taxa and occur when complimentary combinations of traits maximize efficiency of resource exploitation or survival at different points on environmental gradients. 2. Standard metabolic rate (SMR) is a key physiological trait that reflects adaptations to baseline metabolic performance, whereas active metabolism reflects adaptations to variable metabolic output associated with performance related to foraging, predator avoidance, aggressive interactions or migratory movements. Benefits of high SMR and active metabolism may change along a resource (productivity) gradient, indicating that a trade-off exists among active metabolism, resting metabolism and energy intake. 3. We measured and compared SMR, maximal metabolic rate (MMR), aerobic scope (AS), swim performance (UCrit) and growth of juvenile hatchery and wild steelhead and coho salmon held on high- and low-food rations in order to better understand the potential significance of variation in SMR to growth, differentiation between species, and patterns of habitat use along a productivity gradient. 4. We found that differences in SMR, MMR, AS, swim performance and growth rate between steelhead trout and coho salmon were reduced in hatchery-reared fish compared with wild fish. Wild steelhead had a higher MMR, AS, swim performance and growth rate than wild coho, but adaptations between species do not appear to involve differences in SMR or to trade-off increased growth rate against lower swim performance, as commonly observed for high-growth strains. Instead, we hypothesize that wild steelhead may be trading off higher growth rate for lower food consumption efficiency, similar to strategies adopted by anadromous vs. resident brook trout and Atlantic salmon vs. brook trout. This highlights potential differences in food consumption and digestion strategies as cryptic adaptations ecologically differentiating salmonid species. 5. We hypothesize that divergent digestive strategies, which are common and well documented among terrestrial vertebrates, may be an important but overlooked aspect of adaptive strategies of juvenile salmonids, and fish in general.     

Genetic variation of vertebral fusion patterns in coho salmon

The distribution of vertebral fusions along the spinal column differed significantly among crosses from two hatchery stocks of coho salmon, indicating a genetic basis for this character.     

The relationship between river flow and entry to the Aberdeenshire Dee by returning adult Atlantic salmon

One hundred and nine returning adult salmon were radio-tagged in the estuary of the Aberdeenshire Dee, Scotland between February and August 1985 to 1989 and the times when 62 fish entered the river were recorded. Elapsed times between tagging and river entry were significantly greater during periods of lower than average river flows in all months where there were sufficient data to allow statistical comparison. The degree of association between river entry and particular levels of river discharge rate varied seasonally. The proportion of days associated with river entry declined at the lower end of the range of flows available to tagged fish in the summer months. Absolute levels of river discharge played a significant role in modifying the response of salmon to changing flows. During periods of lower than average seasonal flow, river entry was closely associated with days when flow had increased since the previous day. During periods of higher than average flow, river entry was not significantly associated with such periods of increased flow. The results suggest that models which relate river entry by salmon to absolute discharge rates alone are unlikely to be generally reliable.     

Distribution of benthic diatoms in relation to environmental variables in lowland streams

The composition (% relative abundance) of diatom assemblages from soft bottom sediments was studied at 75 sites situated in 46 rivers, brooks, and ditches in the islands of Hiiumaa and Saaremaa and in the lowland of West Estonia. Although the total number of recorded taxa was 205, the studied diatom assemblages consisted of 54, 55, 48, and 50 constant species in the drainage basin of Moonsund, the Gulf of Riga, Hiiumaa, and Saaremaa, respectively. The habitats of the dominating taxa were heterogenous and the most widespread species were Achnanthidium minutissimum, Martyana martyi, Meridion circulare, Cocconeis placentula, Planothidium lanceolatum, and Amphora pediculus. The Shannon–Weaver diversity (H) index varied from 2.09 to 4.63. Multivariate analyses were used to identify the environmental variables governing the composition and structure of the benthic diatom assemblage. Principal Component Analysis (PCA) and Redundancy Analysis (RDA), based on 56 most abundant taxa, indicated differences in the composition and structure of diatom assemblages between different drainage basins as well as between the upper and lower stream courses. In the headwaters there prevailed small epipsammic diatoms (Martyana, Planothidium, Staurosira, Staurosirella). Different motile epipelic species from the genera Amphora, Navicula, Nitzschia, etc. were distributed abundantly in the lower courses of the streams. There was a positive correlation between order of the stream site and trophic level of water (R=0.35; p<0.05). Along a river system, the increasing order of the stream was accompanied by higher trophic level of water.     

Effects of treated sewage on the availability of cadmium to coho salmon

Abstract

Juvenile coho salmon exposed for 30 days to dilutions of sewage treatment plant effluent (STPE) with approximately 2 μg Cd L^?1 showed increased Cd in liver, gill, and kidney tissues. In the liver the increase was unrelated to concentration of STPE, whereas in the gills some treatment effects were apparent in the lower dilutions. In the kidneys, Cd concentration varied inversely with percentage of STPE and levels of total alkalinity as well as total organic carbon in test solutions. It would appear that the ligands in STPE complex Cd and thereby reduce the amount available to bioconcentrate. Neither the average concentration of total Cd nor that of Chelex-labile Cd in the test solutions was indicative of Cd bioavailability in this work.     

Genetic analysis of song dialect populations in Puget Sound white-crowned sparrows

The relationship between cultural variation and biological variationamong natural populations has been the subject of both theoreticaland empirical study. Zonotrichia leucophrys pugetensis is oneof three subspecies of white-crowned sparrow known to form geographicalsong dialects. We investigated whether these dialects correspondto genetic differences among Z. l. pugetensis populations. Wecompared allele frequencies at four microsatellite loci in malesfrom 11 sites spanning six dialects over the subspecies' rangein Oregon and Washington. Cluster analysis and genotype assignmenttests indicated no tendency for sample sites within dialectareas to be genetically more similar than are sites from differentdialect areas. AMOVA tests revealed high within-site variationand low but significant cross-site and cross-dialect-area variation.Finally, genetic distance between sites was not correlated withdialect differences when the effect of geographic distance wascontrolled statistically. We compare our finding of low geneticdifferentiation among Z. l. pugetensis dialect populations toresults of previous studies on Z. l. nuttalli and Z. l. oriantha.Because genetic structuring appears weaker than cultural (songdialect) structure in this species, we discuss the behavioralmechanisms underlying dialect maintenance in the presence ofapparent gene flow.     

Spatio-temporal dynamics of alternative male phenotypes in coho salmon populations in response to ocean environment

1. The coexistence of alternative reproductive phenotypes will probably be shaped by spatial and temporal variability in the environment. However, the effects of such variability on coexistence and the scale at which it operates are seldom understood. 2. To quantify such effects, we examined spatial and temporal dynamics in the abundance and frequency of alternative phenotypes of male coho salmon, Oncorhynchus kisutch Walbaum, which mature as either large fighters (age-3 'hooknoses') or small sneakers (age-2 'jacks'). Using over 20 years of data on coded-wire tagged fish released from nine Oregon hatcheries, we tested for the effects of ocean environment independent of those due to freshwater rearing. 3. Annual fluctuations of the abundance of jack and hooknose males within populations were correlated strongly by brood year (cohort) but not by return year (breeding group). This occurred independently of significant effects of release practice (i.e. the number of fish released, body size at release and date of release), indicating that a synchronized fluctuation in mortality during the first year at sea was the predominant cause. As a result, the annual frequency of the alternative phenotypes at breeding varied considerably within populations. 4. Spatial patterns in the annual fluctuations of the two phenotypes were similar (i.e. synchronous among populations), except that jacks showed local spatial structure (decreased synchrony with distance) not evident among hooknoses. This suggests that oceanic processes affecting the two phenotypes operate at different spatial scales. Despite effects on salmon abundance, the ocean environment had little influence through its effects on salmon growth on the relative frequencies of the alternative phenotypes within and among populations. 5. The results provide insight into the evolutionary dynamics of alternative phenotypes, including an intragenerational time lag that increases annual variability in phenotype frequencies at breeding (return years) and the significance of local freshwater processes, rather than oceanic processes, on phenotype expression. Freshwater processes, such as juvenile growth, timing of migration and breeding competition, operating at evolutionary and intragenerational time-scales, are probably the predominant forces affecting phenotype frequency.     

Movements of hatchery-reared lingcod released on rocky reefs in Puget Sound

Fourteen sub-adult hatchery-reared lingcod (Ophiodon elongatus) were released onto reefs in South Puget Sound, Washington, USA to evaluate their movement behavior. Acoustic telemetry revealed variation in movement among individuals that was related to body size. Larger lingcod tended to leave the release reef sooner than smaller lingcod. Four lingcod left the reefs less than 10 days after release, while three lingcod left between one and 4 months after release. Seven lingcod remained at the release reefs for the entire 5-month study, though they did make apparent short-term (< 24 h duration) excursions away from the reefs. Data suggest that the frequency and duration of excursions increase with age and size in both wild and hatchery lingcod. Movement data from these hatchery lingcod and previously published studies on wild lingcod are compared.     

Ecological management of aquatic plants: effects in lowland streams

Recently, a significant increase in macrophyte growth has been observed in many lowland rivers in Flanders, mainly due to eutrophication and an improvement of the water quality. This growth strongly influences the channel roughness (Manning-n). The first purpose of the project was a better understanding of the complex relationship between biomass development and discharge capacity in lowland rivers. In order to avoid the backing up of water upstream, the whole vegetation body is usually mowed annually. This project also investigated a lighter ecological management of aquatic plants in which only a part of the vegetation is removed in separate and alternating blocks, seeking a compromise between sufficient discharge and conserving large parts of the macrophyte vegetation with all its functions. Beside laboratory experiments, field survey was undertaken in the Grote Caliebeek, a tributary of the Kleine Nete in Flanders, Belgium. The results indicated that the presence of macrophytes in lowland rivers slowed down the waterflow and resulted in a raised water level. The upstream water level followed biomass development at a certain discharge level. The mowing experiments and the field survey indicated that alternating weed cutting patterns can reduce fall in an effective way. This research emphasizes the possibilities of alternating weed cutting patterns in order to deal with water flow problems. In the long term there will be the need for a better understanding of the ecological relationships in the search for a sustainable integrated method of controlling aquatic vegetation.     

Metagenomic Profiling of Microbial Composition and Antibiotic Resistance Determinants in Puget Sound

Human-health relevant impacts on marine ecosystems are increasing on both spatial and temporal scales. Traditional indicators for environmental health monitoring and microbial risk assessment have relied primarily on single species analyses and have provided only limited spatial and temporal information. More high-throughput, broad-scale approaches to evaluate these impacts are therefore needed to provide a platform for informing public health. This study uses shotgun metagenomics to survey the taxonomic composition and antibiotic resistance determinant content of surface water bacterial communities in the Puget Sound estuary. Metagenomic DNA was collected at six sites in Puget Sound in addition to one wastewater treatment plant (WWTP) that discharges into the Sound and pyrosequenced. A total of ∼550 Mbp (1.4 million reads) were obtained, 22 Mbp of which could be assembled into contigs. While the taxonomic and resistance determinant profiles across the open Sound samples were similar, unique signatures were identified when comparing these profiles across the open Sound, a nearshore marina and WWTP effluent. The open Sound was dominated by α-Proteobacteria (in particular Rhodobacterales sp.), γ-Proteobacteria and Bacteroidetes while the marina and effluent had increased abundances of Actinobacteria, β-Proteobacteria and Firmicutes. There was a significant increase in the antibiotic resistance gene signal from the open Sound to marina to WWTP effluent, suggestive of a potential link to human impacts. Mobile genetic elements associated with environmental and pathogenic bacteria were also differentially abundant across the samples. This study is the first comparative metagenomic survey of Puget Sound and provides baseline data for further assessments of community composition and antibiotic resistance determinants in the environment using next generation sequencing technologies. In addition, these genomic signals of potential human impact can be used to guide initial public health monitoring as well as more targeted and functionally-based investigations.