Redd Counts Research Articles

Using genetic pedigree reconstruction to estimate effective spawner abundance from redd surveys: an example involving Pacific lamprey (Entosphenus tridentatus)

Redd surveys are a commonly used technique for indexing the abundance of sexually mature fish in streams; however, substantial effort is often required to link redd counts to actual spawner abundance. In this study, we describe how genetic pedigree reconstruction can be used to estimate effective spawner abundance in a stream reach, using Pacific lamprey (Entosphenus tridentatus) as an example. Lamprey embryos were sampled from redds within a 2.5 km reach of the Luckiamute River, Oregon, USA. Embryos were found in only 20 of the 48 redds sampled (suggesting 58% false redds); however, multiple sets of parents were detected in 44% of the true redds. Estimates from pedigree reconstruction suggested that there were 0.48 (95% CI: 0.29–0.88) effective spawners per redd and revealed that individual lamprey contributed gametes to a minimum of between one and six redds, and in one case, spawned in patches that were separated by over 800 m. Our findings demonstrate the utility of pedigree reconstruction techniques for both inferring spawning-ground behaviors and providing useful information for refining lamprey redd survey methodologies.

Coastal Cutthroat Trout Redd Counts Impacted by Natural Water Supply Variations

AbstractDuring 2001–2003, we counted redds of Coastal Cutthroat Trout Oncorhynchus clarkii clarkii and measured microhabitat variables at fresh redds in Irely Creek upstream of Irely Lake in a largely undisturbed watershed within Olympic National Park, Washington. Redd numbers declined abruptly in 2003, the year after a dry summer caused the dewatering of Irely Lake; therefore, we continued the redd counts during 2004–2012 to determine whether pond dewatering was a factor in the decline and whether redd counts would track Irely Lake surface area. The estimated number of redds varied from a high of 51 (in 2002) to a low of 2 (in 2006, 2007, and 2010); increases in estimated redd number occurred after wetter summers, and decreases were observed after drier summers. This pattern was significant in chi‐square tests for redd number and the change in redd number with Irely Lake condition in the preceding year (dry, semi‐dry, or wet). Rather than indicating juvenile mortality, the lack of a lag in response suggests the mortality of adults that would otherwise have spawned during the subsequent spring. The clear impact of dry summers in one of the wettest regions of North America underscores the important influence of hydrology on fish, even in the absence of other disturbances.Received September 16, 2015; accepted March 15, 2016 Published online July 20, 2016

A Simulation Assessment of Model‐Assisted Estimation of Steelhead Redd Abundance

AbstractRedd abundance for steelhead Oncorhynchus mykiss is frequently estimated using design‐based redd surveys. Redd abundance estimates may be biased low because redds may not be distinguishable prior to or in between sampling events (i.e., removal bias). Removal bias is typically mitigated by increasing temporal sampling intensity, thereby potentially reducing the level of spatial replication. In this study a model‐assisted estimation technique to correct for removal bias was described and evaluated. Parametric survival time models were fit to redd data to estimate redd longevity and parameterize a simulation to evaluate the model‐assisted estimation approach. The simulation showed increasing negative bias in redd counts not adjusted for removal bias as redd longevity decreased and as sampling intervals increased. Average bias among simulated datasets was as high as 43% using raw counts when redd longevity was relatively short at a 25‐d sampling interval. Average bias was reduced to as low 1.3% using the model‐assisted approach. Relative benefits of the model‐assisted approach compared with traditional estimates decreased as redd longevity increased, and the accuracy of model‐assisted estimates were sensitive to the function used to estimate redd longevity. The results of this study suggest that commonly used sampling intervals can potentially be increased with no appreciable increase in bias when using model‐assisted estimation techniques.Received October 7, 2015; accepted March 21, 2016 Published online July 20, 2016

Socially induced reproductive synchrony in a salmonid: an approximate Bayesian computation approach

Reproductive synchrony is a widespread phenomenon found in many taxa, including plants and corals. However, compared with synchrony caused by environmental cues, knowledge of socially induced reproductive synchrony is limited, partly due to the difficulty of experimentally manipulating and/or making detailed behavioral observations of populations in the wild. In this study, we developed a novel modeling framework combining an individual-based model, a hierarchical Bayesian model, and an approximate Bayesian computation (ABC) to elucidate socially induced reproductive synchrony. This method was applied to time-series redd (i.e., spawning nests) count data in 30 wild populations of stream-dwelling Dolly Varden charr. The model with reproductive synchrony explained all the redd count data, whereas the null model, which did not include the synchrony, failed to reproduce the observed data in several populations. In addition, our models suggest that Dolly Varden should be able to adjust spawning by up to a week following other females to produce synchrony. No significant correlation was observed between reproductive timing and environmental factors, suggesting that the major cue for the synchrony was social rather than environmental. The presence of reproductive synchrony within but not among local populations suggests that predator satiation is not the main driver of the synchrony; rather, other mechanisms must exist in the Dolly Varden, such as induced monogamy or polygamy, or avoidance of nest superimposition. This study has demonstrated the effectiveness of using individual-based and hierarchical modeling together with an ABC parameter estimation method in behavioral ecological studies.

Effects of Increased Discharge on Spawning and Age‐0 Recruitment of Rainbow Trout in the Colorado River at Lees Ferry, Arizona

AbstractNegative interactions of Rainbow Trout Oncorhynchus mykiss with endangered Humpback Chub Gila cypha pose challenges to the operation of Glen Canyon Dam (GCD) to manage for both species in the Colorado River. Operations to enhance the Rainbow Trout tailwater fishery may lead to an increase in downstream movement of the trout to areas where they are likely to interact with Humpback Chub. We evaluated the effects of dam operations on age‐0 Rainbow Trout in the tailwater fishery to inform managers about how GCD operations could benefit a tailwater fishery for Rainbow Trout; although this could affect a Humpback Chub population farther downstream. A near year‐long increase in discharge at GCD in 2011 enabled us to evaluate whether high and stable flows led to increased spawning and production of age‐0 Rainbow Trout compared with other years. Rainbow Trout spawning was monitored by fitting a model to observed redd counts to estimate the number of redds created over a spawning season. Data collected during electrofishing trips in July–September and November were used to acquire age‐0 trout population and mortality rate estimates. We found that high and stable flows in 2011 resulted in 3,062 redds (1.7 times the mean of all survey years) and a population estimate of 686,000 age‐0 Rainbow Trout (second highest on record). Despite high initial abundance, mortality remained low through the year (0.0043%/d) resulting in significant recruitment with a record high November population estimate of 214,000 age‐0 Rainbow Trout. Recent monitoring indicates this recruitment event was followed by an increase in downstream migration, which may lead to increased interactions with downstream populations of Humpback Chub. Consequently, while our results indicate that manipulating flow at GCD can be used to manage Rainbow Trout spawning and recruitment, fisheries managers should use flow manipulation in moderation to minimize downstream migration in order to reduce negative interactions with other species in the Colorado River.Received September 8, 2014; accepted March 28, 2015

Impact of beaver dams on abundance and distribution of anadromous salmonids in two lowland streams in Lithuania.

European beaver dams impeded movements of anadromous salmonids as it was established by fishing survey, fish tagging and redd counts in two lowland streams in Lithuania. Significant differences in abundancies of other litophilic fish species and evenness of representation by species in the community were detected upstream and downstream of the beaver dams. Sea trout parr marked with RFID tags passed through several successive beaver dams in upstream direction, but no tagged fish were detected above the uppermost dam. Increase in abundances of salmonid parr in the stream between the beaver dams and decrease below the dams were recorded in November, at the time of spawning of Atlantic salmon and sea trout, but no significant changes were detected in the sections upstream of the dams. After construction of several additional beaver dams in the downstream sections of the studied streams, abundance of Atlantic salmon parr downstream of the dams decreased considerably in comparison with that estimated before construction.

Spawning Patterns of Pacific Lamprey in Tributaries to the Willamette River, Oregon

AbstractAddressing the ongoing decline of Pacific Lamprey Entosphenus tridentatus across its range along the west coast of North America requires an understanding of all life history phases. Currently, spawning surveys (redd counts) are a common tool used to monitor returning adult salmonids, but the methods are in their infancy for Pacific Lamprey. To better understand the spawning phase, our objective was to assess temporal spawning trends, redd abundance, habitat use, and spatial patterns of spawning at multiple spatial scales for Pacific Lamprey in the Willamette River basin, Oregon. Although redd density varied considerably across surveyed reaches, the observed temporal patterns of spawning were related to physical habitat and hydrologic conditions. As has been documented in studies in other basins in the Pacific Northwest, we found that redds were often constructed in pool tailouts dominated by gravel, similar to habitat used by spawning salmonids. Across the entire Willamette Basin, Pacific Lampreys appeared to select reaches with alluvial geology, likely because this is where gravel suitable for spawning accumulated. At the tributary scale, spawning patterns were not as strong, and in reaches with nonalluvial geology redds were more spatially clumped than in reaches with alluvial geology. These results can be used to help identify and conserve Pacific Lamprey spawning habitat across the Pacific Northwest.Received May 16, 2014; accepted July 16, 2014

Evaluating the Accuracy and Precision of Multiple Abundance Estimators Using State‐Space Models: A Case Study for a Threatened Population of Chinook Salmon in Johnson Creek, Idaho

AbstractOver the last century, Chinook Salmon Oncorhynchus tshawytscha populations in the Pacific Northwest have experienced dramatic declines, leading to many of them being listed as threatened under the Endangered Species Act. The abundance of these threatened populations relative to the thresholds for delisting remains the primary metric for assessing recovery, yet determining the true population abundances from multiple survey types with unknown levels of accuracy and precision remains difficult. The abundance of the spring–summer Chinook Salmon population in Johnson Creek, Idaho, has been measured using a mark–recapture survey and three different redd count surveys (RCSs) that vary temporally and spatially. Using a state‐space model, we determined the accuracy and precision of each survey type by decoupling the observation error of the survey from the process error describing the annual variability in the true population abundance. We then extended the results of the model to determine the risk of managers’ incorrectly delisting the population (a type I error) or incorrectly keeping it listed (a type II error). Finally, we show that salmon managers with data‐limited populations (primarily those with only single‐pass index RCSs) might use the results of our risk analysis to determine whether expanding survey efforts to minimize management risks is appropriate when they are confronted with dwindling financial resources. For example, we determined that although both the multiple‐pass extended RCS (CV = 0.06) and mark–recapture surveys (CV = 0.14) provide unbiased estimates of salmon abundance in Johnson Creek, the mark–recapture study can have annual costs that are 30–100 times greater. Managers may determine that directing research funds toward acquiring information unique to weir‐based mark–recapture surveys (i.e., migration timing, good genetics samples, etc.) may not be justified for all populations.Received October 7, 2013; accepted March 5, 2014

Using Spatial Resampling to Assess Redd Count Survey Length Requirements for Pacific Lamprey

AbstractPacific Lamprey Entosphenus tridentatus has declined across its range along the West Coast of North America, and an understanding of all life history phases is needed to address population recovery. Spawning surveys (redd counts) are common tools currently used to monitor returning adult salmonids, but such methodologies are in their infancy for Pacific Lamprey. Our objective was to assess the minimum spawning survey distance required to detect the presence of Pacific Lamprey redds and obtain precise redd density estimates from these data. To do this, we statistically resampled existing spawning locations of Pacific Lamprey collected during spawning surveys in four streams of the Willamette River Basin, Oregon, during spring of 2013. We found that the minimum survey distance for Pacific Lamprey redd detection was inversely related to the observed redd density and was always less than 1.2 km. Survey distance requirements to obtain precise redd counts (±20% of observed redd densities) were also inversely related to redd density and habitat availability, and varied between 1.3 km and 13.7 km. Our results suggest that spawning surveys are a potential tool for monitoring adult Pacific Lamprey abundance, but the specific objectives of the monitoring programs and acknowledgment of unknowns must be considered prior to implementation into recovery plans.Received January 2, 2014; accepted May 19, 2014

Population Changes after 14 Years of Harvest Closure on a Migratory Population of Bull Trout in Idaho

AbstractPrimary data (size and age structure, abundance) and derived data (growth, mortality, recruitment) were used to assess the status and trends of Bull Trout Salvelinus confluentus in the North Fork of the Clearwater River, Idaho, under a 14‐year harvest closure. From 2000 (6 years after harvest closure) to 2008, an increase in the number of larger and older migratory Bull Trout occurred, as evidenced by the rightward shift in the cumulative length‐frequency distribution, increases in mean total length and weight, and increases in age. The stability in growth rates over an 8‐year interval indicated that the increases in size structure were age related (e.g., recruitment and mortality changes) rather than growth related. The abundance of migratory spawning adults also steadily increased over the period 1994–2008, as indicated by the increases in redd counts. A logistic model fitted to population estimates (not including unsampled portions of the drainage where migratory Bull Trout are known to exist) indicated that the rate of population growth as of 2005 was beginning to slow and that a carrying capacity of 5,215 total migratory adults will be asymptotically approached, surpassing the U.S. Fish and Wildlife Service's drainage‐wide recovery goal of 5,000 total adults. The results from an age‐structured population model (model 1) indicated a carrying capacity (5,716 migratory adults) similar to that of the logistic model. If the results under model 1 are achieved, the migratory adult population (including nonspawning adults) will surpass 5,000 adults in 2019. The results under a second model depicted a lower carrying capacity (3,592 fish). This analytical approach has promise for application in situations where harvest restrictions or the elimination of fishing are part of Bull Trout restoration programs.Received August 8, 2013; accepted December 11, 2013

Bull Trout Trends in Abundance and Probabilities of Persistence in Idaho

AbstractWe estimated the population growth rates of Bull Trout Salvelinus confluentus and used population growth models to evaluate observation error and estimate Bull Trout persistence probabilities by using 25 data sets (averaging 19 years of record) that indexed abundance across Idaho. These data sets were derived from a variety of fish sampling techniques, including weirs, screw traps, redd counts, daytime snorkeling, electrofishing, and angler creel. Bull Trout populations in Idaho were relatively stable prior to 1994, but after 1994, substantially more population growth rates trended statistically upward (n = 14) than downward (n = 3). Average intrinsic rates of population change were 0.01 (SE = 0.03) prior to 1994 and 0.07 (SE = 0.02) after 1994; across all years of data, the rate of change averaged 0.07 (SE = 0.02). Fifty‐nine percent of the data sets had zero to minimal observation error according to Gompertz state‐space model estimates; observation error was least common in data from screw traps and redd counts and most common in snorkel data. Gompertz‐type density‐dependent models were most often the best‐fitting models for Bull Trout population growth. Moreover, few of the most reliable modeling results (i.e., those from data sets estimated to have zero to minimal observation error) contained a period effect or time (i.e., year) effect, suggesting that carrying capacity generally did not differ between the pre‐1994 and post‐1994 periods and generally was not trending positively or negatively through time. Parametric bootstraps predicted that the mean probability of falling below the quasi‐extinction level of 20 adults in the next 30 years was 9.8% (median = 4.7%) for data sets estimated to have zero to minimal observation error. The weight of evidence from our modeling results suggests that for most Bull Trout populations in Idaho, abundance is stable or increasing and the risk of extirpation in the foreseeable future is low.Received March 12, 2013; accepted November 18, 2013Published online February 10, 2014

A Legacy of Divergent Fishery Management Regimes and the Resilience of Rainbow and Cutthroat Trout Populations in Lake Crescent, Olympic National Park, Washington

Abstract As a means to increase visitation, early fisheries management in the National Park Service (NPS) promoted sport harvest and hatchery supplementation. Today, NPS management objectives focus on the preservation of native fish. We summarized management regimes of Olympic National Park's Lake Crescent, which included decades of liberal sport harvest and hatchery releases of 14.3 million salmonids. Notably, nonnative species failed to persist in the lake. Complementary analyses of annual redd counts (1989–2012) and genetics data delineated three sympatric trout (one rainbow; two cutthroat) populations that exhibited distinct spatial and temporal spawning patterns, variable emergence timings, and genetic distinctiveness. Allacustrine rainbow trout spawned in the lake outlet from January to May. Cutthroat trout spawned in the major inlet tributary (Barnes Creek) from February to June and in the outlet river (Lyre) from September to March, an unusual timing for coastal cutthroat trout. Redd counts for ea...

Genetic‐Based Estimates of Adult Chinook Salmon Spawner Abundance from Carcass Surveys and Juvenile Out‐Migrant Traps

AbstractDue to the challenges associated with monitoring in riverine environments, unbiased and precise spawner abundance estimates are often lacking for populations of Pacific salmon Oncorhynchus spp. listed under the Federal Endangered Species Act. We investigated genetic approaches to estimate the 2009 spawner abundance for a population of Columbia River Chinook Salmon Oncorhynchus tshawytscha via genetic mark–recapture and rarefaction curves. The marks were the genotyped carcasses collected from the spawning area during the first sampling event. The second sampling event consisted of a collection of juveniles from a downstream migrant trap located below the spawning area. The parents that assigned to the juveniles through parentage analysis were considered the recaptures, which was a subset of the genotypes captured in the second sample. Using the Petersen estimator, the genetic mark–recapture spawner abundance estimates based on the binomial and hypergeometric models were 910 and 945 Chinook Salmon, respectively. These results were in agreement with independently derived spawner abundance estimates based on redd counts, area‐under‐the‐curve methods, and carcass tagging based on the Jolly–Seber model. Using a rarefaction curve approach, which required only the juvenile offspring sample, our estimate of successful breeders was 781 fish. Our genetic‐based approaches provide new alternatives to estimate adult Pacific salmon abundance in challenging environmental conditions or for populations with poor or unknown estimates of precision.

Spawning Success of Bull Trout Transported above Main‐Stem Clark Fork River Dams in Idaho and Montana

AbstractThree main‐stem dams have fragmented the Clark Fork River in Montana and Idaho for nearly 100 years. Since 2001, Bull Trout Salvelinus confluentus collected below the farthest downstream dam, Cabinet Gorge Dam, have been manually transported upstream so that they can return to natal spawning tributaries and contribute gametes to numerically depressed populations upstream from the dams. Although redd counts and radio telemetry data suggest that these adults attempted to spawn after upstream transport, spawning success has not been documented or quantified. We used genetic parentage assignments to determine whether adult Bull Trout were successfully spawning after being transported upstream. Parentage data were also used to examine reproductive success and spawning behavior of fish transported upstream (transports) as well as Bull Trout that spawned in the same tributaries but were not transported upstream (nontransports). We genotyped 1,362 juvenile Bull Trout collected in two Clark Fork River tributaries, East Fork Bull River and Graves Creek, from 2008 to 2010 as well as 184 adult Bull Trout collected below Cabinet Gorge Dam and in Clark Fork River tributaries from 2004 to 2010. Parentage data indicated that Bull Trout collected below Cabinet Gorge Dam did spawn after upstream transport; nearly 27% of the juveniles sampled in this study had at least one upstream transport parent. Reproductive success varied widely among the adults we assigned as parents. We observed a variety of spawning patterns including adults that spawned only once, annual repeat spawners, and alternate‐year spawners. Our data provide evidence that the upstream transport program is meeting its goal of increasing the number of spawning adults in Bull Trout populations upstream from Clark Fork River dams and highlights the fact that nontransported fish also make an important contribution to the local tributary populations.Received January 29, 2013; accepted August 28, 2013

Evaluating Salmon Spawning Habitat Capacity Using Redd Survey Data

AbstractManagement and recovery goals for fish populations often rely on estimating the number of fish that can be supported by finite habitats. In the absence of direct measures of carrying capacity, management decisions are commonly informed by results of habitat models. However, the shortcomings and spatially explicit nature of most habitat models result in making assumptions, often preclude inclusion of important variables, and are rarely validated at the reach level. We analyze long‐term, redd‐count data for a population of Chinook Salmon Oncorhynchus tshawytscha to evaluate spawning habitat capacity of a major river. Adult escapement generally increased during the years 1994–2012; consequently site use and total redd counts also increased. Together, the annual use of spawning sites and the redd counts (as functions of adult escapement) provided evidence for density‐dependent changes in the availability and capacity of spawning sites. Redd counts exceeded one recovery criterion specific to one spawning aggregate of the population during 11 years of our survey data, supporting the conclusion that adequate spawning habitat is available to attain a management goal set for this aggregate.Received May 31, 2012; accepted March 27, 2013

Estimating spatial distribution of Atlantic salmon escapement using redd counts despite changes over time in counting procedure: application to the Allier River population

AbstractIn salmonid species, such as Atlantic salmon (Salmo salar L.), the most frequent type of data set available related to adult escapements are redd counts. When collected over a broad spatio‐temporal domain, redd counts data are of great interest for tracking the variation through time of the spatial distribution of the potential spawners. This is important for management purposes when the habitat quality is variable across river sections of a catchment or when the spatial distribution can vary depending on management actions or on environmental factors. However, long‐term data sets are prone to changes in data collection methodology. In this article, we present a new hierarchical Bayesian modelling approach that allows both (i) to account for a change in the data collection procedure and (ii) to analyse the variation through time of the potential spawners’ spatial distribution. The value of the proposed approach is demonstrated by its application to the Atlantic salmon redd counts data collected in Allier (France) catchment from 1977 to 2011. The Allier can be divided into three main sections according to management and habitat considerations, and an important change occurred in the redd data collection in 1997: counts by foot or by boat were replaced by counts from a helicopter. A significant effect of this change on methodology is detected: less redds counted when using the helicopter counts. However, its explicit consideration in the modelling makes little difference with regard to the estimates of potential spawner abundance and their associated uncertainty.

Movements by Adfluvial Bull Trout during the Spawning Season between Lake and River Habitats

AbstractMovements of adfluvial Bull Trout Salvelinus confluentus were evaluated with acoustic telemetry during spawning seasons 2006–2011 in Chester Morse Lake,Washington. Ninety‐six percent of the individuals made multiple trips between the lake and river habitat during the spawning season,which lasted from less than 1 day to more than a month. Male Bull Trout took an average 13.2 (± 8.7 SD) trips,while females averaged 18.0 (± 14.0 SD) trips. Directional movement between the lake and a river occurred throughout the day; however,the distribution of movement activity was bimodal,peaking from 0600 to 0900 hours (downstream movement) and from 1700 to 2000 hours (upstream movement). The majority of time spent in the river per trip occurred during nighttime hours for female (mean = 74%) and male Bull Trout (mean = 72%). While spawning activity was not confirmed for each trip,this study illustrates an as‐yet unreported movement pattern of adfluvial Bull Trout during the spawning season. These results are relevant to managers considering monitoring population trends by way of redd count surveys because multiple redd sites per spawning season are possible,a situation that could lead to overestimating population numbers. Additional research to determine whether spawning occurs on individual trips would help assess whether population numbers could be overestimated by simply using redd counts in systems similar to the one studied.

Comparative Dispersal Patterns for Recolonizing Cedar River Chinook Salmon above Landsburg Dam, Washington, and the Source Population below the Dam

AbstractAnadromous salmonid populations are particularly vulnerable to migration blockages, such as dams and culverts, because access to historic spawning and rearing habitats is prevented. The process of salmonid recolonization has not been well documented for river systems where anthropogenic migration barriers have been removed or where fish passage facilities have been constructed. In September 2003, Seattle Public Utilities completed construction of a fish passage facility that circumvented Landsburg Dam on the Cedar River, Washington. Chinook Salmon Oncorhynchus tshawytscha spawned in newly available main‐stem habitats immediately after fish passage facility construction and in all subsequent years. Further dispersal into tributary habitats occurred 5 years after construction. Redds tended to be concentrated in the downstream third of the available habitat above the dam, although some fish did utilize suitable spawning sites throughout the main stem, even in the uppermost reaches of the newly available habitat. Median spawn timing for redds observed above the dam was not significantly different from spawn timing for the source population, indicating that migration delays through the fish passage facility were minimal. Male Chinook Salmon consistently outnumbered females, with annual sex ratios ranging from 1.3:1 to 4.7:1. Chinook Salmon spawning above the dam contributed between 2.7% and 14.7% of the total annual redd count (2003–2010) for Cedar River Chinook Salmon; upstream redds as a percentage of total redds increased over time, indicating that a new, naturally reproducing population above the dam was growing. The proportion of hatchery‐origin fish spawning above the dam decreased over the duration of the study but was consistently higher than the hatchery component observed below the dam.

Impacts of Highway Construction on Redd Counts of Stream‐Dwelling Brook Trout

AbstractSedimentation during road construction is a human impact that threatens aquatic ecosystems. Despite a large body of literature on the effect of fine sediments on the initial developmental stages of fish, we do not know of any studies that have investigated the return of spawners to spawning grounds in streams impacted by sediment from road construction. The objective of this study was to quantify the return to spawning grounds of brook trout Salvelinus fontinalis at different stages of highway construction (before, during, and after construction). Redd counts were made at a fine spatial resolution (<0.5 m) over two consecutive years in 12 reaches distributed along a 115‐km stretch of highway in the Laurentides Wildlife Reserve, Quebec. We found a significant decrease in redd counts in reaches affected by construction during the second year but no evidence of impacts in reaches affected by construction during the first year. A possible explanation is that sediment releases were well controlled during construction except after an extreme weather event occurring during the spawning season of the second year. However, we observed that a reach heavily impacted by sediments still supported high densities of spawners. Overall, we found a significant decrease in the absolute number of redd counts in the second year but strong consistency in the spatial distribution of the spawning sites, both within and among reaches and for all stages of highway construction and sediment loadings, which suggests that the return of spawners is more constrained by habitat variables than by sediment from highway construction.Received March 30, 2012; accepted August 20, 2012

A Study of the Spawning Ecology and Early Life History Survival of Bonneville Cutthroat Trout

AbstractWe completed a large‐scale field experiment in four tributaries of the Logan River, Utah, where the largest metapopulation of imperiled Bonneville cutthroat troutOncorhynchus clarkii utahpersists. We documented the spatial and temporal distributions of spawners, quantified substrate use versus substrate availability, and evaluated differences in hatch and emergence fry success between and among sites in relation to habitat characteristics. We observed considerable variability in the timing, magnitude, and duration of spawning among study areas (streams), in part as a function of a variable, multipeaked hydrograph. Nevertheless, across study areas, >70% of redds were constructed on the final descending limb of the hydrograph. Despite large differences in the amount of spawning substrate available, Bonneville cutthroat trout utilized a narrow range of substrate and sizes (3–80 mm) similar to that utilized by other subspecies of cutthroat trout, albeit biased towards larger sizes. Water temperatures generally remained below the recommended range (6–17°C) for spawning; however, the viability of this metapopulation of cutthroat trout suggests that the recommended temperature range for spawning is overestimated for this subspecies and (or) does not account for local thermal adaptation. Hatch varied from 43% to 77% and emergence survival from 39% to 65% among streams, and within‐stream variability was substantial; both survival rates declined significantly as a function of increased fine sediment concentrations. Egg development rates were nearly 50% greater in a high‐elevation tributary where redd counts were also lowest. In high, mountain systems with short growing seasons, this incubation delay likely presents a significant growth disadvantage for age‐0 trout. Our research enhances our understanding of Bonneville cutthroat trout spawning ecology and early survival and provides critical information for aiding in the development of benchmarks for their recovery. Effective conservation efforts should be directed towards minimizing anthropogenic activities that result in excess sedimentation in their critical spawning tributaries.Received April 15, 2011; accepted February 7, 2012