Snake River Research Articles

Status of Redband Trout and Nonnative Trout in the Wood River Basin, Idaho

Abstract The Wood River Basin in central Idaho has been isolated from the surrounding Snake River Basin by Malad Gorge Falls for at least 50,000 years, and recent genetic analyses suggest that Redband Trout Oncorhynchus mykiss gairdneri in the basin represent a previously undescribed lineage. To assess their contemporary status, we electrofished 22 study reaches in 2021-2022 previously occupied by Redband Trout when originally surveyed in 2003. Our objective was to assess changes in the occurrence and density of Redband Trout, Brook Trout Salvelinus fontinalis, and Brown Trout Salmo trutta. In 2021-2022, Redband Trout were absent in 5 of the 22 originally occupied reaches with Brook Trout as the only salmonid species present at all extirpated reaches. Brook Trout have now been extirpated from two reaches previously occupied with Redband Trout as the only salmonid species present at both reaches. Brown Trout colonized one new reach since 2003 and are now present at all study reaches (n = 3) which exceed 10 m average stream wetted width. Average fish density increased from 2003 to 2021-2022 across all study reaches for total trout (all species combined) and at nearly all study reaches for each individual trout species. Changes in Redband Trout density were unrelated to changes in nonnative trout density. On average Redband Trout composition (of all trout at each reach) across all study reaches decreased by 13% while Brook Trout and Brown Trout increased by 8% and 4%, respectively from 2003 to 2021-2022. Nevertheless, Brook Trout are increasingly present in headwater streams while Brown Trout occupy larger, lower elevation rivers, potentially threatening the long-term conservation of Redband Trout in the Wood River Basin. Although additional data is warranted to more completely understand the distribution of trout, these preliminary results suggest that management activities may be necessary to control the further spread of nonnative salmonids in the basin.

Riparian Methylmercury Production Increases Riverine Mercury Flux and Food Web Concentrations.

The production and uptake of toxic methylmercury (MeHg) impacts aquatic ecosystems globally. Rivers can be dynamic and difficult systems to study for MeHg production and bioaccumulation, hence identifying sources of MeHg to these systems is both challenging and important for resource management within rivers and main-stem reservoirs. Riparian zones, which are known biogeochemical hotspots for MeHg production, are understudied as potential sources of MeHg to rivers. Here, we present a comprehensive quantification of the hydrologic and biogeochemical processes governing MeHg concentrations, loads, and bioaccumulation at 16 locations along 164 km of the agriculturally intensive Snake River (Idaho, Oregon USA) during summer baseflow conditions, with emphasis on riparian production of MeHg. Approximately one-third of the MeHg load of the Snake River could not be attributed to inflowing waters (upgradient, tributaries, or irrigation drains). Across the study reach, increases in MeHg loads in surface waters were significantly correlated with MeHg concentrations in riparian porewaters, suggesting riparian zones were likely an important source of MeHg to the Snake River. Across all locations, MeHg concentrations in surface waters positively correlated with MeHg concentrations in benthic snails and clams, supporting that riparian produced MeHg was assimilated into local aquatic food webs. This study contributes new insights into riparian MeHg production within rivers which can inform mitigation efforts to reduce MeHg bioaccumulation in fish.

Development and application of a genetic baseline to inform bull trout (Salvelinus confluentus) passage and conservation in the Snake River

Development and application of a genetic baseline to inform bull trout (Salvelinus confluentus) passage and conservation in the Snake River

Using Empirical Performance Data to Source Bluebunch and Snake River Wheatgrass Plant Materials to Restoration Sites in the Eastern Great Basin, USA.

To infer adaptation of plant material, restoration practitioners often consider only surrogate geographic or climatic information. However, empirical biomass data could assist in deciding what material to use where. To test this approach, we transplanted seven bluebunch wheatgrass (BBWG; Pseudoroegneria spicata) and five Snake River wheatgrass (SRWG; Elymus wawawaiensis) populations to three sites ranging from low to high precipitation (LPPT, MPPT, and HPPT). We measured establishment-year (2011) biomass at all sites and 2012-16 biomass at MPPT and HPPT. When data were standardized by site, P-7 and Anatone produced the mostBBWG biomass across sites and Wahluke the least in both 2011 and 2012-16, while E-58X produced the most SRWG biomass and Secar and E-49X the least in 2011 and 2012-16, respectively. Among BBWG populations in 2011, relative performance of P-7 (G6 generation) and Goldar increased and Whitmar decreased at wetter sites, while Columbia was stable (high) and Wahluke was stable (low) over sites. Among SRWG populations in 2011, Secar, Secar78, and E-58X increased at drier sites and Discovery at wetter sites. However, once established, populations of both species were much more similar for trend. In 2012-16, trend somewhat increased for five BBWG populations from MPPT to HPPT, was stable for Wahluke, but declined for Columbia, while all five SRWG populations declined at HPPT. These results suggest that, once established, BBWG is mostly stable across sites, while SRWG is less adapted to wetter sites. In 2012-16, BBWG populations originating at drier (or wetter) sites mostly performed relatively better at MPPT (or HPPT), suggesting adaptation to site. However, in the establishment year (2011), this relationship did not hold, suggesting seedling vigor and immature growth rate play a stronger role than precipitation at the site of origin.

Detecting bias in abundance estimates of spawning fish from closed‐capture models using remote and physical capture data

AbstractObjectiveMixed‐data models incorporating remote antenna detections from PIT‐tagged fish together with physical capture data (mixed data) can improve precision of mark–recapture abundance estimates, particularly for spawning fish. However, if the entire population is not available for physical capture during the mark–recapture sampling period, abundance estimates will be biased low. Our objectives were to examine bias and precision of two modeling approaches and develop a simple diagnostic to determine whether the entire population was sampled.MethodsWe use a simulation modeling approach to compare specified abundances with abundance estimates from closed‐capture models using mixed data (the mixed‐data approach) and using only marked (e.g., PIT‐tagged) individuals divided by the proportion of individuals that are marked (proportional approach). We use the difference in bias between the two models as our diagnostic of whether a population was randomly sampled. We then applied our diagnostic to two case studies: a spawning population of adfluvial June Sucker Chasmistes liorus in Utah Lake, Utah, 2008–2020, and a spawning population of Bull Trout Salvelinus confluentus in the Imnaha River, a tributary of the Snake River, Oregon, 2013–2020.ResultSimulation experiments revealed that the mixed‐data approach became increasingly negatively biased as the proportion of the population that was unavailable for physical capture increased, yet the proportional approach remained unbiased. Abundance estimates from the proportional approach averaged approximately 6× greater for June Sucker and 2× greater for Bull Trout compared to the mixed‐data approach, suggesting a proportion of the population was not available for physical capture in both case studies.ConclusionUnderstanding the magnitude of bias in abundance estimates is particularly important for the management of imperiled species that are subject to recovery plans. Comparing estimates using the unbiased proportional approach that we described here with those from a mixed‐data approach when PIT tag detection data are used to estimate abundance is a straightforward method to evaluate bias in these estimates.

Correction: Leeman et al. U-Pb LA-ICP-MS Zircon Dating of Crustal Xenoliths: Evidence of the Archean Lithosphere Beneath the Snake River Plain. Minerals 2024, 14, 578

There were three errors in the original publication [...]

Estimating the effects of smolt size and migration timing on salmon marine survival using a multivariate mixed‐effect model

Abstract When the conditions encountered by a migratory species are highly variable, the timing of migration and migrant condition are critical to survival. Spring/summer‐run Chinook salmon in the Snake River of the Northwestern United States are listed as threatened under the US Endangered Species Act because of decades of poor adult returns; juvenile smolt‐to‐adult survival is often 0.5% or less. Juveniles pass through eight dams en route to the ocean, and despite changes to the hydropower system, there has been little recent improvement in survival. We analysed the effect of migration date, fish length and their interaction on the survival to adulthood of 409,747 wild juvenile Chinook salmon as they migrated through a large, dynamic riverine ecosystem and through the ocean, measured over 20 years. Parametric 2D smoothers are often used to quantify unexplained heterogeneity across space; however, these same statistical models can be applied to 2D datasets to uncover patterns of covariance of two biological processes important to management actions. We employ Gaussian Markov random fields (GMRF) and a 2D smoother to estimates of fish survival to identify the nature of variation in survival with respect to length and date. We found significant effects of fish length, migration date and the date‐by‐length interaction on resulting riverine and marine survival. Unlike the gradual shifts in survival in relation to length and timing that marginal estimates demonstrate, we show that within year, changes in survival with length and timing are often more abrupt than previously thought. Synthesis and applications: Inter‐annually, we identified distinct combinations of fish length and migration timing leading to elevated smolt‐to‐adult survival. Often these ‘hotspots’ are compressed into fish sizes greater than 100 mm and passage timings of only a week or two, demonstrating that even modest shifts in body size and migration timing can have a significant effect on survival. Further research can concentrate on these distinct annual periods to identify sources of mortality that have previously been elusive.

Assessing Methods to Monitor Aquatic Invertebrates in a Large River: Comparing Rock Baskets and Hess Samplers in the Snake River, Wyoming, USA

Large rivers are difficult to sample due to their size yet critical to monitor because humans heavily rely upon and alter them. Aquatic invertebrates are commonly used to assess the ecosystem quality of streams, but methods to sample large rivers are underdeveloped. We sampled aquatic invertebrates using a Hess sampler and rock baskets in the Snake River near Jackson, Wyoming, USA. Hess samples collected more aquatic invertebrate taxa and a higher proportion of Ephemeroptera, Plecoptera, and burrowing taxa. Rock baskets collected a higher proportion of Trichoptera, filterers, and clinging taxa. Bioassessment metrics differed between sampling methods; richness, diversity, evenness, Ephemeroptera, Plecoptera, and Trichoptera (EPT), and Hilsenhoff’s biotic index produced higher values in Hess samples, and percent EPT was higher in rock baskets. Non-metric multidimensional scaling and analysis of similarity indicated that the samplers collected different assemblages (p < 0.001). The standard error of total invertebrate density was smaller and most taxa were collected with seven replicate samples. Understanding how sampling methods alter the aquatic invertebrates collected will help managers develop monitoring protocols that are best suited to the river and collect the most unbiased invertebrate assemblages.

Cycles in adult steelhead length suggest interspecific competition in the North Pacific Ocean

Anadromous fishes rely on abundant prey in the ocean to grow large quickly, but prey limitation leads to interspecific competition. When species interactions are difficult to observe, growth can be studied to detect otherwise cryptic signals of competition. We describe a previously undocumented 2-year cycle in the lengths of adult natural-origin steelhead ( Oncorhynchus mykiss) returning to spawn in the Snake River Basin. Returning steelhead were 38 mm shorter on odd return years, not accounting for sex, stock, and years of ocean residence. The well-known cycle in abundance of pink salmon ( Oncorhynchus gorbuscha) from eastern Kamchatka and North America had statistically significant negative effects on returning steelhead lengths that depended on sex and the number of years of ocean residence. These results suggest that competition for limited resources occurs well after initial ocean entry and that interactions during later stages of ocean residence can be influential. Interspecific competition has implications for future returns of steelhead from the ocean, especially as metabolic demands for steelhead increase as the ocean warms.

Can Agricultural Managed Aquifer Recharge (Ag‐MAR) Recover Return Flows Under Prior Appropriation in a Warming Climate?

AbstractGroundwater return flow to streams is important for maintaining aquatic habitat and providing water to downstream users, particularly in irrigated watersheds experiencing water scarcity. However, in many agricultural regions, increased irrigation efficiency has reduced return flows and their subsequent in‐stream benefits. Agricultural managed aquifer recharge (Ag‐MAR)—where artificial recharge is conducted via irrigation canals and agricultural fields—may be a tool to recover these return flows, but implementation is challenged by water supply and water management. Using climate‐driven streamflow simulations, an integrated operations‐hydrology model, and a regional groundwater model, we investigated the potential for Ag‐MAR to recover return flows in the Henrys Fork Snake River, Idaho (USA). We simulated potential Ag‐MAR operations for water years 2023–2052, accounting for both future water supply conditions and local water management rules. We determined that Ag‐MAR operations reduced springtime peak flow at the watershed outlet by 10%–14% after accounting for return flows. Recharge contribution to streamflow peaked in July and November, increasing July–August streamflow by 6%–14% and November–March streamflow by 9%–14%. Furthermore, sites where Ag‐MAR was conducted incidental to flood irrigation had more water available for recharge, compared to sites requiring recharge rights, which are junior in priority to agricultural rights. Mean annual recharge volume for the incidental recharge sites averaged 12% of annual natural streamflow, ranged from 269 to 335 Mm3, and was largely available in April and October. We demonstrate Ag‐MAR can effectively recover groundwater return flows when applied as flood irrigation on agricultural land with senior‐priority water rights.

Back from the brink: Estimating daily and annual abundance of natural-origin salmon smolts from 30-years of mixed-origin capture-recapture data

Evaluating the status and trends of natural-origin anadromous fish populations over time requires robust estimates of out-migrating juvenile abundance. Information on abundance is typically acquired by capturing actively migrating fish as they pass stationary monitoring platforms. Challenges to estimation include protracted migration timing, temporally varying capture probabilities and the contemporaneous presence of unmarked hatchery-origin fish. The confounding effects of unmarked hatchery fish are especially pernicious in systems hosting multiple hatchery programs with variable mark-rates among releases. Here, we address this problem for a regionally and culturally important population of Chinook salmon (Oncorhynchus tshawytscha) supported by a hatchery-supplementation program implemented in response to the listing of this population under the U.S. Endangered Species Act. We developed a model to estimate daily and annual abundance of naturally produced age-0 fall Chinook salmon passing Lower Granite Dam (Snake River, USA) for each of the last 30 years. We accounted for variable hatchery marking rates by integrating two related data sources: 1) release-recapture data of fish with individually identifiable tags and 2) counts of marked and unmarked sample of fish captured each day. We fit joint parameters for daily fish arrival and capture probabilities to these data to estimate the daily abundance of hatchery- and natural-origin fish. Our results show that from 1992 to 2021, the annual abundance of juvenile natural-origin Snake River fall Chinook salmon increased by two orders of magnitude. These results are the first comprehensive evaluation of multi-decadal trends in abundance and run-timing for this population. Our approach can be adapted to other runs and locations within the Columbia River basin or similar systems where out-migrating fish are monitored at fixed locations.

Nonnative Smallmouth Bass in the Snake River, Idaho: Population Dynamics, Demographics, and Management Options

Abstract The Snake River in Idaho, USA, supports a popular sport fishery for nonnative Smallmouth Bass Micropterus dolomieu, but there are limited studies on the population dynamics of this introduced species in Idaho and other water systems in the western United States. The purpose of this study was to describe the population dynamics and demographics of Smallmouth Bass in the Snake River, Idaho. In total, we sampled 4,929 Smallmouth Bass during electrofishing surveys on the Snake River (separated into nine segments) and three major tributaries (Boise, Payette, and Weiser rivers). We estimated age for 1,869 Smallmouth Bass sampled from the Snake River (n = 1,433) and three tributaries (n = 436). Catch-per-unit-effort for all nine segments combined on the Snake River was 36.6 fish/h (±4.4 SE). In the tributaries, catch-per-unit-effort varied from 43.6 to 125.0 fish/h. Relative weight of all Smallmouth Bass varied from 86 to 107, indicating that fish were in relatively good body condition. Fish in the system grew fast, with relative growth index values often near or exceeding 100 for all age classes. Total annual mortality for the Snake River was 45.1 ± 0.7%, and it was 36.8–40.5% in the tributaries. Furthermore, we estimated exploitation to be 5.3% (90% CI; ±2.2%) for the Snake River and tributaries combined. We used a yield-per-recruit population model to evaluate the effects of varying minimum length limits on the fishery. With the observed population demographics and exploitation rates, increasing the current minimum length limit from 305 mm to 356 or 406 mm would probably have little influence on the number of Smallmouth Bass available to anglers. However, increasing the length limit would result in reduced biomass available for harvest. The potential for recruitment overfishing was minimal for all minimum length limits and levels of exploitation. As such, changes to current harvest regulations do not appear warranted. Our findings provide important information on the population dynamics of Smallmouth Bass that can be useful in evaluating their management across Idaho and in similar systems in western North America.

A Pore-Scale Phase Field Model for CO2-Fluid-Basalt Interactions.

Basalt is a suitable target area for CO2 storage. Clarifying the evolution of the pore structure during CO2-fluid-basalt interactions is a crucial element in the preparation of a CO2 geologic storage operation. In this study, a pore-scale phase field model is proposed to simulate the CO2-fluid-basalt interaction process of Snake River Plain basalt. Our model is suitable for complex multimineral natural rocks, and the initial mineral distribution before the reaction can be completely based on a real 3D rock image without the need to simplify the mineral geometry. The simulation results demonstrate that after 120 days of dissolution-precipitation reaction, the volume of secondary minerals (3.75%) exceeds that of dissolved minerals (2.01%), leading to a reduction in porosity by 1.74%. The pore structure of the basalt changes significantly, and the connectivity is obviously reduced. The effects of temperature and pressure on the reaction rate were examined to guide site selection for CO2 sequestration. The results show that increasing temperature and pressure can accelerate the reaction rate, but the impact of pressure on the reaction rate is negligible compared to the significant influence of temperature. Therefore, an area with a high geothermal gradient is conducive to geological sequestration.

Alignment between water inputs and vegetation green‐up reduces next year's runoff efficiency

AbstractIn the western United States, water supplies largely originate as snowmelt from forested land. Forests impact the water balance of these headwater streams, yet most predictive runoff models do not explicitly account for changing snow‐vegetation dynamics. Here, we present a case study showing how warmer temperatures and changing forests in the Henrys Fork of the Snake River, a seasonally snow‐covered headwater basin in the Greater Yellowstone Ecosystem, have altered the relationship between April 1st snow water equivalent (SWE) and summer streamflow. Since the onset and recovery of severe drought in the early 2000s, predictive models based on pre‐drought relationships over‐predict summer runoff in all three headwater tributaries of the Henrys Fork, despite minimal changes in precipitation or snow accumulation. Compared with the pre‐drought period, late springs and summers (May–September) are warmer and vegetation is greener with denser forests due to recovery from multiple historical disturbances. Shifts in the alignment of snowmelt and energy availability due to warmer temperatures may reduce runoff efficiency by changing the amount of precipitation that goes to evapotranspiration versus runoff and recharge. To quantify the alignment between snowmelt and energy on a timeframe needed for predictive models, we propose a new metric, the Vegetation‐Water Alignment Index (VWA), to characterize the synchrony of vegetation greenness and snowmelt and rain inputs. New predictive models show that in addition to April 1st SWE, the previous year's VWA and summer reference evapotranspiration are the most significant predictors of runoff in each watershed and provide more predictive power than traditionally used metrics. These results suggest that the timing of snowmelt relative to the start of the growing season affects not only annual partitioning of streamflow, but can also determine the groundwater storage state that dictates runoff efficiency the following spring.

How do Management Goals for Wild Chinook Salmon Align with Feasibility?

Evaluation of goals is crucial for effective management to conserve viable and diverse fish populations and to support harvest. Management of wild Chinook Salmon Oncorhynchus tshawytscha in the Snake River basin exemplifies the struggle to meet fisheries goals. Considering contemporary production of juvenile emigrants, it is imperative to determine the survival from emigration to adult (Se‐a) required to meet abundance goals. Increased anthropogenic impact on spawning and rearing habitats leads to higher Se‐a required to attain goals. Wilderness populations exhibit viability and could sustain fisheries with Se‐a lower than required elsewhere. Conversely, populations targeted for habitat restoration demand higher Se‐a to fulfill goals, indicating a need to enhance egg‐to‐smolt survival. However, Se‐a has fallen below the threshold needed for replacement in all populations, even at current low abundances. Despite these challenges, most populations still possess the potential to achieve abundance goals, emphasizing the importance of strategic interventions to bolster their resilience.

U-Pb LA-ICP-MS Zircon Dating of Crustal Xenoliths: Evidence of the Archean Lithosphere Beneath the Snake River Plain

U-Pb LA-ICP-MS Zircon Dating of Crustal Xenoliths: Evidence of the Archean Lithosphere Beneath the Snake River Plain

Illegal shooting of protected nongame birds along power lines coincides with places and times of peak legal recreational shooting

Abstract Illegal killing of protected nongame birds is pervasive and can be demographically relevant. In 2021 and 2022, we evaluated spatial and temporal patterns in illegal killing of birds along 69.7 km of power lines in the Morley Nelson Snake River Birds of Prey National Conservation Area in Idaho, USA, to provide insight into potential drivers behind the activity and key information to manage this threat across the American west. The illegal shooting of 8 species of raptors and corvids we documented was clumped both temporally and spatially, as opposed to being randomly distributed across the year and landscape. We found 72 illegally shot birds, most killed during spring months (March to May), coincident with peak time periods of legal recreational shooting activity, and in places with high levels of recreational shooting. We also found evidence of targeted killing of raptors in the conservation area in areas not associated with recreational shooting. Given the numbers of nesting pairs of some local raptor species, this shooting is likely demographically relevant for some but not all local populations. Likewise, with the prevalence of recreational shooting across the American west, the inference we draw is broadly relevant beyond our Idaho study area. The insight our work provides can enable owners of power lines, law enforcement agencies, and resource managers to coordinate in outreach, regulatory, and law enforcement action to manage a threat that may have widespread impacts for some avian species.

Cow-calf chute side data collection in the field and its role in cow-calf consultation

Cattle Health and Reproduction LLC is a private vet practice located in the Snake River valley of Idaho servicing east Idaho and southwest Montana. It primarily serves beef cattle produc­ers with a major focus on large cow-calf operations with herds of 250 to 3,500 mother cows. The practice also services stocker/ yearling/feedlot operators and has a growing embryo transfer division. The practice retains a strong service-oriented approach with significant involvement in the herd management of its cli­ents. Data collection and information management has been a focus of the practice over the past couple of years and has aided in the development of a consultation leg of the practice.

Joint prioritization of best-management-practice projects to optimally improve agricultural-drain-outlet water quality

The judicious application of conservation funds to mitigate non-point source pollution from agricultural runoff continues to be a practical challenge, particularly when presented with multiple feasible types of best-management-practices. To address this challenge, we develop and demonstrate a joint prioritization of two best-management-practice types that are commonly implemented to reduce pollutant loads from agricultural activities: irrigation-system-efficiency-upgrades and sediment-retention-basins. The goal of the joint prioritization is to optimally apply conservation funds to maximize pollutant-load reductions at agricultural-drain outlets. We achieve large computational efficiencies in the joint prioritization by leveraging a novel, graph-based mixed-integer-nonlinear-programming model. The computational efficiencies allow the approach to be applied as a large-scale scoping analysis to identify sets of high priority projects for further investigation. We demonstrate the approach on an agricultural basin in southwestern Idaho which drains to the Snake River. For our demonstration site, the results indicate that while larger load reductions are possible using irrigation-system-efficiency-upgrades alone, including sediment-retention-basins can provide more cost-effective outcomes. We present the results in the form of cost curves that illustrate the Pareto-optimal trade-offs between load reductions and costs (i.e., multi-objective Pareto fronts). We compare solutions that only include irrigation-system-efficiency-upgrades against those that also include sediment-retention-basins. We do not consider solutions with sediment-retention-basins only due to the limited availability of potential sites compared to irrigation-system-efficiency-upgrades. In our demonstration example, the cost curves including sediment-retention-basins provide more cost-effective solutions than with irrigation-system-efficiency-upgrades alone. Therefore, the inclusion of sediment-retention-basins can increase the beneficial use of conservation funds to improve agricultural-drain-discharge water quality. Given that participation in irrigation-system-efficiency-upgrade programs is voluntary for landowners, we also explore the effect of recruitment uncertainty. We identify that as the recruitment percentage increases, the effect of sediment-retention-basin selection on project prioritization increases. The insights derived from this type of analysis can ensure that conservation funds are optimally applied to maximize benefits to water quality.

Predicting juvenile-to-adult survival in Chinook salmon using non-lethal scale-derived growth and regeneration indices

ABSTRACT Survival is often associated with body size, growth rate, and stress, but the latter two are more difficult to observe non-lethally. Non-lethal methods can be particularly important for endangered and culturally valuable species. With fish scales, growth and stress indices could be inferred without needing to sacrifice fish. We examined scales from ~350 wild Chinook salmon (Oncorhynchus tshawytscha) in Valley Creek and at Lower Granite Dam (Pacific Northwest, USA) in 2007–2019. From a von Bertalanffy model and scale circulus spacings, we estimated a brood-year-specific growth coefficient K (hereafter K ˆ ). Using the scale-derived K ˆ and other biological and environmental covariates, we examined how these potential predictors associated with juvenile-to-adult survival of >136,000 passive-integrated-transponder-tagged Chinook salmon from the Snake River Basin (Pacific Northwest, USA). We found that the effects on survival from brood-year-specific K ˆ , fork length of the tagged individuals, and interaction between K ˆ and fork length were positive. We also determined that the proportion of fish samples with regenerated scales (an indicator of stress) had a negative effect on survival. For further refinement of non-lethal, scale-derived indices on survival, we encourage examination of indices across populations, juvenile habitats, and juvenile life stages, and not simply a regional, brood-year-specific growth index.