Fluvial rainbow trout contribute to the colonization of steelhead (Oncorhynchus mykiss) in a small stream

Life history polymorphisms provide ecological and genetic diversity important to the long term persistence of species responding to stochastic environments. Oncorhynchus mykiss have complex and overlapping life history strategies that are also sympatric with hatchery populations. Passive integrated transponder (PIT) tags and parentage analysis were used to identify the life history, origin (hatchery or wild) and reproductive success of migratory rainbow/steelhead for two brood years after barriers were removed from a small stream. The fluvial rainbow trout provided a source of wild genotypes to the colonizing population boosting the number of successful spawners. Significantly more parr offspring were produced by anadromous parents than expected in brood year 2005, whereas significantly more parr offspring were produced by fluvial parents than expected in brood year 2006. Although hatchery steelhead were prevalent in the Methow Basin, they produced only 2 parr and no returning adults in Beaver Creek. On average, individual wild steelhead produced more parr offspring than the fluvial or hatchery groups. Yet, the offspring that returned as adult steelhead were from parents that produced few parr offspring, indicating that high production of parr offspring may not be related to greater returns of adult offspring. These data in combination with other studies of sympatric life histories of O. mykiss indicate that fluvial rainbow trout are important to the conservation and recovery of steelhead and should be included in the management and recovery efforts.     

Beaver dams maintain fish biodiversity by increasing habitat heterogeneity throughout a low‐gradient stream network

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Effects of travertine and flow on leaf retention in Fossil Creek,Arizona

Leaf retention is important in transferring energy from riparian trees to stream food webs. Retention increases with geomorphic complexity such as substrate coarseness, sinuosity, and the presence of debris dams. High discharge can reduce retention, particularly when streams lack physical trapping features. Travertine formations, caused by calcium carbonate deposition, can alter stream morphology. To date, however, we know of no study testing the effect of travertine on leaf retention. This study capitalized on a river restoration project in Fossil Creek, Arizona, where water was returned to the channel after a century of diversion. We examined how the fixed factors Flow (before and after restoration) and Morphology (travertine and riffle-pool sites) affected leaf retention. Leaf retention was higher in sites where travertine forms barriers across the river, relative to sites with riffle-pool morphology. Most leaves retained in travertine reaches were concentrated at the bottom of pools formed between dams. Although flow restoration did not alter retention rates across all sites, it diminished them at travertine sites, indicating an interaction between stream flow and morphology. We conclude that stream complexity and leaf retention are enhanced by travertine deposition but that high discharge can reduce the retentive capacity of in-stream structures. Handling editor: Darren Ryder     

A Comparison of Genetic Variation Between an Anadromous Steelhead, Oncorhynchus mykiss, Population and Seven Derived Populations Sequestered in Freshwater for 70 Years

In 1926 cannery workers from the Wakefield Fisheries Plant at Little Port Walter in Southeast Alaska captured small trout, Oncorhynchus mykiss, from a portion of Sashin Creek populated with a wild steelhead (anadromous O. mykiss) run. They planted them into Sashin Lake which had been fishless to that time and separated from the lower stream by two large waterfalls that prevented upstream migration of any fish. In 1996 we sampled adult steelhead from the lower creek and juvenile O. mykiss from an intermediate portion of the creek, Sashin Lake, and five lakes that had been stocked with fish from Sashin Lake in 1938. Tissue samples from these eight populations were compared for variation in: microsatellite DNA at 10 loci; D-loop sequences in mitochondrial DNA; and allozymes at 73 loci known to be variable in steelhead. Genetic variability was consistently less in the Sashin Lake population and all derived populations than in the source anadromous population. The cause of this reduction is unknown but it is likely that very few fish survived to reproduce from the initial transplant in 1926. Stockings of 50–85 fish into five other fishless lakes in 1938 from Sashin Lake did not result in a similar dramatic reduction in variability. We discuss potential explanations for the observed patterns of genetic diversity in relation to the maintenance of endangered anadromous O. mykiss populations in freshwater refugia.     

Rapid flow through the sediments of a headwater stream in the southern Appalachians

SUMMARY. 1. The flow of water through the sediment layer (underflow) of streams can influence nutrient uptake dynamics and the supply of materials to microbes, meiofauna and macroinvertebrates living within stream sediments. We examined the extent of underflow in Hugh White Creek, a headwater stream in the southern Appalachian Mountains and compared underflow at different depths and at different sites within the stream.
2. Initially rhodamine dye was used to trace the flow of water through the sediments; however, the dye was strongly absorbed by the sediments in Hugh White Creek. Thus rhodamine was not suitable as a tracer of water flow. Chloride reacted conservatively in laboratory experiments and was used as a tracer.
3. The tracer infiltrated the sediments within 5 min to depths of 10 cm at all six sites. Chloride infiltration tended to decrease with depth of sediments at all sites although there was no consistent statistical pattern in chloride concentration with depth for the different sites. Equilibrium between the water column and sediments was reached rapidly, within minutes for the sites with coarse sediments and within a few hours for sites with finer sediments. Minimum rates of chloride infiltration into the sediments ranged between 1.0 cm min⁻¹ for the sites with cobble substrate to 0.2 cm min⁻¹ for sites with fine sand sediments associated with debris dams. These data suggest that underflow may be a major component in the functioning of Appalachian mountain streams.     

Obstructions in Vascular Networks: Relation Between Network Morphology and Blood Supply

We relate vascular network structure to hemodynamics after vessel obstructions. We consider tree-like networks with a viscoelastic fluid with the rheological characteristics of blood. We analyze the network hemodynamic response, which is a function of the frequencies involved in the driving, and a measurement of the resistance to flow. This response function allows the study of the hemodynamics of the system, without the knowledge of a particular pressure gradient. We find analytical expressions for the network response, which explicitly show the roles played by the network structure, the degree of obstruction, and the geometrical place in which obstructions occur. Notably, we find that the sequence of resistances of the network without occlusions strongly determines the tendencies that the response function has with the anatomical place where obstructions are located. We identify anatomical sites in a network that are critical for its overall capacity to supply blood to a tissue after obstructions. We demonstrate that relatively small obstructions in such critical sites are able to cause a much larger decrease on flow than larger obstructions placed in non-critical sites. Our results indicate that, to a large extent, the response of the network is determined locally. That is, it depends on the structure that the vasculature has around the place where occlusions are found. This result is manifest in a network that follows Murray’s law, which is in reasonable agreement with several mammalian vasculatures. For this one, occlusions in early generation vessels have a radically different effect than occlusions in late generation vessels occluding the same percentage of area available to flow. This locality implies that whenever there is a tissue irrigated by a tree-like in vivo vasculature, our model is able to interpret how important obstructions are for the irrigation of such tissue.     

Local habitat conditions explain the variation in the strength of self‐thinning in a stream salmonid

Self-thinning patterns are frequently used to describe density dependence in populations on timescales shorter than the organism''s life span and have been used to infer carrying capacity of the environment. Among mobile animals, this concept has been used to document density dependence in stream salmonids, which compete over access to food and space. The carrying capacity, growth conditions, and initial cohort sizes often vary between streams and stream sections, which would influence the onset and strength of the density dependence. Despite much effort in describing habitat relationships in stream fishes, few studies have explicitly tested how the physical environment affects the slope of the thinning curves. Here, we investigate the prevalence and strength of self-thinning in juvenile stages of a steelhead (Oncorhynchus mykiss) population in Idaho, USA. Further, we investigate the roles of local physical habitat and metabolic constraints in explaining the variation in thinning curves among study sites in the watershed. Only yearling steelhead exhibited an overall significant thinning trend, but the slope of the mass–density relationship (−0.53) was shallower than predicted by theory and reported from empirical studies. There was no detectable relationship in subyearling steelhead. Certain abiotic factors explained a relatively large portion of the variation in the strength of the self-thinning among the study reaches. For subyearling steelhead, the slopes were negatively associated with the average water depth and flow velocity in the study sites, whereas slopes in yearlings were steeper in sites that incurred a higher metabolic cost. Our results show that the prevalence and strength of density dependence in natural fish populations can vary across heterogeneous watersheds and can be more pronounced during certain stages of a species'' life history, and that environmental factors can mediate the extent to which density dependence is manifested in predictable ways.     

Iteroparity in complex mating systems of steelhead Oncorhynchus mykiss (Walbaum)

This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss . Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River = 7·5% and Salmon River = 9·4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18·2%), Imnaha River (17·4%), Pahsimeroi Hatchery (25·2%) and Asotin Creek (22·2%). A lack of correlation between population escapement size and kelt proportions ( P > 0·05) suggests that iteroparity was not uniformly expressed across populations, but was significantly negatively correlated with body size ( P < 0·05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations.     

Archival and acoustic tags reveal the post-spawning migrations, diving behavior, and thermal habitat of hatchery-origin Sacramento River steelhead kelts (Oncorhynchus mykiss)

Acoustic and geolocating archival tags were deployed on steelhead kelts to study their post-spawning migrations, diving behavior and thermal habitat. Fourteen reconditioned steelhead kelts were surgically implanted with LAT2510 archival and V7-2 L acoustic tags, and released from Coleman National Fish Hatchery. An array of acoustic receivers in the Sacramento River and Delta, and the San Francisco Bay estuary detected the downstream movement of the steelhead. Two steelhead kelts (J and M) with archival tags were recovered at the hatchery after 219 and 285 days at liberty respectively. Based on changes in geolocations, vertical movements, and water temperatures, the migrations of steelhead J and M were divided into five and six phases respectively. Steelhead J moved into coastal California waters while steelhead M remained in freshwater for the majority of its time at liberty. Large increases in temperature and opacity were recorded before and after the ocean phases, likely as the steelhead moved through the Sacramento Delta. Both steelhead kelts remained relatively close to the surface throughout their migration but there were diurnal differences in the vertical movements. In freshwater, the steelhead tended to be deeper during the day (e.g., steelhead J: 3.08?±?1.50 vs 1.65?±?1.15 m, day vs night) but in the ocean, the steelhead were typically deeper during the night (1.32?±?1.61 vs 5.63?±?6.11 m). Both steelhead kelts appeared to be less oceanic than a previous study in Scott Creek, a small coastal stream approximately 100 km south of the mouth of San Francisco Bay. Although this study has a small sample size, the results suggest that steelhead kelts from a large river and estuary system, like the Sacramento River, may be relatively less oceanic than steelhead kelts from small coastal streams.     

Stream flow, salmon and beaver dams: roles in the structuring of stream fish communities within an anadromous salmon dominated stream

The current paradigm of fish community distribution is one of a downstream increase in species richness by addition, but this concept is based on a small number of streams from the mid-west and southern United States, which are dominated by cyprinids. Further, the measure of species richness traditionally used, without including evenness, may not be providing an accurate reflection of the fish community. We hypothesize that in streams dominated by anadromous salmonids, fish community diversity will be affected by the presence of the anadromous species, and therefore be influenced by those factors affecting the salmonid population. Catamaran Brook, New Brunswick, Canada, provides a long-term data set to evaluate fish community diversity upstream and downstream of an obstruction (North American beaver Castor canadensis dam complex), which affects distribution of Atlantic salmon Salmo salar. The Shannon Weiner diversity index and community evenness were calculated for sample sites distributed throughout the brook and over 15 years. Fish community diversity was greatest upstream of the beaver dams and in the absence of Atlantic salmon. The salmon appear to depress the evenness of the community but do not affect species richness. The community upstream of the beaver dams changes due to replacement of slimy sculpin Cottus cognatus by salmon, rather than addition, when access is provided. Within Catamaran Brook, location of beaver dams and autumn streamflow interact to govern adult Atlantic salmon spawner distribution, which then dictates juvenile production and effects on fish community. These communities in an anadromous Atlantic salmon dominated stream do not follow the species richness gradient pattern shown in cyprinid-dominated streams and an alternative model for stream fish community distribution in streams dominated by anadromous salmonids is presented. This alternative model suggests that community distribution may be a function of semipermeable obstructions, streamflow and the distribution of the anadromous species affecting resident stream fish species richness, evenness, biomass and production.     

Early Marine Migration Patterns of Wild Coastal Cutthroat Trout (Oncorhynchus clarki clarki), Steelhead Trout (Oncorhynchus mykiss), and Their Hybrids

Background

Hybridization between coastal cutthroat trout (Oncorhynchus clarki clarki) and steelhead or rainbow trout (Oncorhynchus mykiss) has been documented in several streams along the North American west coast. The two species occupy similar freshwater habitats but the anadromous forms differ greatly in the duration of marine residence and migration patterns at sea. Intermediate morphological, physiological, and performance traits have been reported for hybrids but little information has been published comparing the behavior of hybrids to the pure species.

Methodology/Principal Findings

This study used acoustic telemetry to record the movements of 52 cutthroat, 42 steelhead x cutthroat hybrids, and 89 steelhead smolts, all wild, that migrated from Big Beef Creek into Hood Canal (Puget Sound, Washington). Various spatial and temporal metrics were used to compare the behavior of the pure species to their hybrids. Median hybrid residence time, estuary time, and tortuosity values were intermediate compared to the pure species. The median total track distance was greater for hybrids than for either cutthroat or steelhead. At the end of each track, most steelhead (80%) were located near or north of the Hood Canal, as expected for this seaward migrating species, whereas most cutthroat (89%) were within 8 kilometers of the estuary. Most hybrids (70%) were detected leaving Hood Canal, though a substantial percentage (20%) remained near the Big Beef Creek estuary. More hybrids (7.5%) than pure cutthroat (4.5%) or steelhead (0.0%) were last detected in the southern reaches of Hood Canal.

Conclusions/Significance

Given the similarity in freshwater ecology between the species, differences in marine ecology may play an important role in maintaining species integrity in areas of sympatry.     

Benthic invertebrate assemblage change following dam removal in a Wisconsin stream

Small dams (height <10 m) have transformed stream networks across the United States. Shopiere Dam was removed from Turtle Creek, a fourth order stream in Southeastern Wisconsin in the fall of 1999. We sampled three sites (upstream of the impoundment, immediately below the dam, and farther downstream) before and after dam removal to identify changes in the invertebrate assemblage following removal. Prior to removal, upstream and downstream sites had similar taxonomic composition. In contrast the dam site had more taxonomic variation. The upstream, dam and downstream sites responded differently to dam removal in analyses of diversity, functional feeding groups, and invertebrate composition. Upstream at the reference site, changes in functional feeding group composition appeared to be associated with a decrease in silt coverage. At the dam site, taxonomic composition changed following dam removal, however diversity and functional feeding groups remained similar. At the downstream site, the invertebrate assemblage remained similar in all analyses. Our observations indicate that the effects of dam removal were not uniform through the stream, rather each site responded in a different way.     

Livestock grazing limits beaver restoration in northern New Mexico

The North American beaver (Castor canadensis) builds dams that pond water on streams, which provide crucial ecological services to aquatic and riparian ecosystems and enhance biodiversity. Consequently, there is increasing interest in restoring beavers to locations where they historically occurred, particularly in the arid western United States. However, despite often intensive efforts to reintroduce beavers into areas where they were severely reduced in numbers or eliminated due to overharvesting in the eighteenth and nineteenth centuries, beavers remain sparse or missing from many stream reaches. Reasons for this failure have not been well studied. Our goal was to evaluate certain biotic factors that may limit the occurrence of dam‐building beavers in northern New Mexico, including competitors and availability of summer and winter forage. We compared these factors at primary active dams and at control sites located in stream reaches that were physically suitable for dam‐building beavers but where none occurred. Beaver dams mostly occurred at sites that were not grazed or where there was some alternative grazing management, but were mostly absent at sites within Forest Service cattle allotments. Results indicated that cattle grazing influenced the relation between vegetation variables and beaver presence. The availability of willows (Salix spp.) was the most important plant variable for the presence of beaver dams. We conclude that grazing by cattle as currently practiced on Forest Service allotments disrupts the beaver‐willow mutualism, rendering stream reaches unsuitable for dam‐building beavers. We recommend that beaver restoration will require changes to current livestock management practices.     

Survival of captured and relocated adult spring-run Chinook salmon Oncorhynchus tshawytscha in a Sacramento River tributary after cessation of migration

We studied the efficacy of the process for capture and upstream relocation of 26 adult spring-run Chinook salmon in Butte Creek, California in 2009. These fish had ceased volitional upstream migration prior to reaching their summer holding habitat. The purpose of the relocation was to move fish upstream of two water diversion dams and release them in a part of the stream from which they could presumably swim to cool summer holding habitat, then spawn in the fall. Fish were netted, transported by truck, given an esophageal radio tag/temperature tag, and released. Radio tagging proved to be a useful technique for determining the survival and movement of relocated fish and temperature tags provide useful information to determine thermal exposure and time of death. Twenty-three tags (88 %) were recovered, compared with a 10 % tag recovery rate for an earlier study using fin clips. Most tags were recovered within 3.5 km upstream and 1 km downstream of the release site. A single tag was recovered 6 km upstream. No fish were determined to have survived to spawn. Temperature tag data indicate that most of the salmon died within 2–6 days after the relocation operation. After preventative measures have been exhausted, future relocations efforts, in any setting, should consider (1) intervention as soon as fish cease volitional migration but before they are exposed to further deleterious conditions (2) monitoring environmental conditions to choose appropriate release sites (3) evaluation of disease transmission risk, and (4) handling practices that minimize potential stress due to air immersion and thermal shock.     

Restricted gene flow between resident Oncorhynchus mykiss and an admixed population of anadromous steelhead

The species Oncorhynchus mykiss is characterized by a complex life history that presents a significant challenge for population monitoring and conservation management. Many factors contribute to genetic variation in O. mykiss populations, including sympatry among migratory phenotypes, habitat heterogeneity, hatchery introgression, and immigration (stray) rates. The relative influences of these and other factors are contingent on characteristics of the local environment. The Rock Creek subbasin in the middle Columbia River has no history of hatchery supplementation and no dams or artificial barriers. Limited intervention and minimal management have led to a dearth of information regarding the genetic distinctiveness of the extant O. mykiss population in Rock Creek and its tributaries. We used 192 SNP markers and collections sampled over a 5‐year period to evaluate the temporal and spatial genetic structures of O. mykiss between upper and lower watersheds of the Rock Creek subbasin. We investigated potential limits to gene flow within the lower watershed where the stream is fragmented by seasonally dry stretches of streambed, and between upper and lower watershed regions. We found minor genetic differentiation within the lower watershed occupied by anadromous steelhead (F_ST = 0.004), and evidence that immigrant influences were prevalent and ubiquitous. Populations in the upper watershed above partial natural barriers were highly distinct (F_ST = 0.093) and minimally impacted by apparent introgression. Genetic structure between watersheds paralleled differences in local demographics (e.g., variation in size), migratory restrictions, and habitat discontinuity. The evidence of restricted gene flow between putative remnant resident populations in the upper watershed and the admixed anadromous population in the lower watershed has implications for local steelhead productivity and regional conservation.     

Diel movements of out-migrating Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) smolts in the Sacramento/San Joaquin watershed

We used ultrasonic telemetry to describe the movement patterns of late-fall run Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) smolts during their entire emigration down California’s Sacramento River, through the San Francisco Bay Estuary and into the Pacific Ocean. Yearling hatchery smolts were tagged via intracoelomic surgical implantation with coded ultrasonic tags. They were then released at four upriver locations in the Sacramento River during the winters of 2007 through 2010. Late-fall run Chinook salmon smolts exhibited a nocturnal pattern of migration after release in the upper river. This is likely because individuals remain within a confined area during the day, while they become active at night and migrate downstream. The ratio between night and day detections of Chinook salmon smolts decreased with distance traveled downriver. There was a significant preference for nocturnal migration in every reach of the river except the Estuary. In contrast, steelhead smolts, which reside upriver longer following release, exhibited a less pronounced diel pattern during their entire migration. In the middle river, Delta, and Estuary, steelhead exhibited a significant preference for daytime travel. In the ocean Chinook salmon preferred to travel at night, yet steelhead were detected on the monitors equally during the night and day. These data show that closely related Oncorhynchus species, with the same ontogenetic pattern of out-migrating as yearlings, vary in migration tactic.     

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

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

Kinship analysis of Pacific salmon: insights into mating, homing, and timing of reproduction

Multilocus microsatellite genotypes were used to infer kinship and relatedness in two species of Pacific salmon from three populations in Washington State. Even in the absence of direct genetic data from parents, clustering of individuals according to allele sharing and reconstruction of parental genotypes allowed resolution of full- and half-sib relationships among 135 chinook salmon (Oncorhynchus tshawytscha) sampled as preemergent juveniles from 14 redds in the Dungeness River. Inferred reproductive behaviors included single-pair matings, polyandry in which females mated with two to three males at a single redd, polygyny in which males mated with two females at different redds, use of two redds by a single female, and use of one redd site by two females. Greater average relatedness (rxy) in the upper reach of the Dungeness River implied within-reach homing of returning adults. In steelhead trout (O. mykiss), the frequency of related pairs (dyads) of mature individuals that migrated up Snow Creek less than a week apart was greater than expected for randomly chosen dyads, as was the frequency of steelhead dyads that were spawned on the same day in the Forks Creek hatchery. These results imply a heritable basis for upstream migration date and maturation date in steelhead trout.     

Interactions between endangered wild and hatchery salmonids: can the pitfalls of artificial propagation be avoided in small coastal streams?

Hatchery and wild juvenile populations of steelhead Oncorhynchus mykiss and coho salmon Oncorhynchus 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.