ABSTRACT Objective Dams impede fish movement and can isolate riverine populations into defined areas. The Alabama River is divided into four major sections by three lock-and-dam structures. Here, we used otolith microchemistry and genetic techniques to quantify potential movements and population connectivity among these river sections for two fish species (Freshwater Drum Aplodinotus grunniens and White Crappie Pomoxis annularis) that differ in life expectancies, spawning strategies, and swimming abilities. Methods We collected water samples throughout the study area to quantify spatial variation in trace element ratios, and we collected fish from the four river sections defined by the three lock-and-dam structures to quantify spatial variation in their otolith trace element ratios and their population genetic structure. Results Trace element ratios (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) in water samples collected throughout the study area varied spatially but were temporally consistent. Broad patterns in water chemistry were reflected in element : Ca ratios in otolith whole transects (i.e., across entire life), edges (reflecting time of capture), and cores (reflecting early life). Correlations between otolith edge and season-specific water Sr:Ca ratios from the areas where fish were collected were significant for both species, while the associations between otolith edges and water were mostly nonsignificant for Mg:Ca, Mn:Ca, and Ba:Ca ratios. Linear discriminant analyses were used to determine how accurately the multivariate element signatures in otolith edges could classify fish back to the river sections from which they were collected, resulting in mixed accuracies between species. Genetic structure was present in both species but was weaker in Freshwater Drum than in White Crappie, indicating that barriers have had a greater influence on White Crappie genomics than on Freshwater Drum genomics. Overall, there was little support for either species showing substantive movement past the lock-and-dam structures. Conclusions Our results based on both otolith microchemistry and genetics suggest that movement of these species past dams is very limited. Individuals of both species generally appear to remain in areas near where they hatched; although movements among habitats may occur, both upstream and downstream dam passage events appear rare. Efforts at increasing connectivity, if successful in attracting and moving fish, would increase opportunities for movement, thus increasing gene flow beyond its highly restricted current state.

ABSTRACT Objective Reproductive activity is rarely observed directly in the White Sturgeon Acipenser transmontanus because spawning generally occurs over benthic habitats in fast-flowing rivers. Aspects of reproductive ecology have been inferred from indirect lines of evidence, with results often being imprecise. Here we performed parentage analysis within the population of the upper Columbia River, associating adults with offspring that had been collected from multiple years and locations, to precisely characterize spawning periodicity across years, spawning duration within years, and spawning site fidelity across locations. Methods We identified parent–offspring relationships by integrating Mendelian-mismatch-based exclusion, likelihood-based assignment, and relationship coefficient analysis, using tetrasomic single-nucleotide polymorphism genotypes that were produced through genotyping-in-thousands by sequencing. The thresholds for each approach were determined from known parent–offspring relationships in a cultured population. Results Parent–offspring relationships associated adults of both sexes with multiple spawning events across years, within years, and across locations. Among adults that were linked to multiple years, spawning periodicity ranged from 1 to 5 years in males and 4 to 5 years in females. Among adults that were associated with multiple spawning dates within years, we observed spawning durations of up to 26 d in males, whereas females largely displayed durations up to 4 d. Individuals of both sexes were associated with different sites in different years, whereas males were further linked to different sites within years, suggesting incomplete spawning site fidelity. Conclusions These findings inform an ongoing conservation aquaculture program for supplementing this population and demonstrate the utility of parentage analysis for inferring reproductive behaviors in high detail, particularly in systems where thorough sampling of parents and offspring is feasible.

ABSTRACT Objective Though native to the Columbia River basin, Northern Pikeminnow Ptychocheilus oregonensis have been the subject of long-term population control. This began in response to their increased predation of anadromous juvenile salmonids as a result of habitat modification due to hydropower dam construction. The Northern Pikeminnow Management Program (NPMP) is a targeted harvest program with a sport reward fishery that has been operating in the Columbia and lower Snake rivers since 1991. As a result of this sport reward fishery, over 5.7 million piscivorous (≥200 mm FL) Northern Pikeminnow have been harvested for cash rewards. Each year, data are collected to monitor and evaluate the program; however, the program has come under scrutiny in recent years due to analytical methods that have not changed since the program’s inception. Northern Pikeminnow have been PIT-tagged through the NPMP since 2003 to estimate the program’s annual exploitation rate, with a goal of 10–20%, which feeds into an estimate of the program’s annual reduction in predation. The model used to estimate the annual exploitation rate assumes closed populations separated by dams, an assumption that relies on limited evidence generated largely before PIT tag technology was deployed in the region. After being tagged, most Northern Pikeminnow are never recaptured, but PIT tag antennas passively track their movement. Methods We combined data from the Columbia basin PIT Tag Information System database with detailed NPMP tagging and harvest data to measure Northern Pikeminnow movement throughout the Columbia River basin over two decades. Results Movement records reveal that individuals traveled at least as far as 968 km. Nearly 13% of Northern Pikeminnow tagged through the NPMP were detected in different river sections, separated by dams, from where they were initially tagged. Movement in tributaries and across main-stem dams reflects seasonal patterns aligned with Northern Pikeminnow upstream spawning migration and out-migration of juvenile salmonids. Conclusions Our increased understanding of Northern Pikeminnow movement informs the calculation of the exploitation rate, one of the key measures of NPMP success. Further, as the NPMP evolves over time, information on Northern Pikeminnow movement may also contribute to future management strategies, like focusing removals on river reaches in which immigration outpaces emigration.

ABSTRACT Objective Understanding the “who, what, when, where, and why” of angler harvest is a critical component of managing fisheries with harvest-based regulations. Previous research has suggested that these are complex questions deserving further examination at broader spatiotemporal scales. Here, we use a long-term creel survey data set to develop models for predicting likelihood of fish harvest using a suite of explanatory variables. Methods We used creel survey data to summarize 831,479 records of fish angled from Kansas waters between 1997 and 2024 (excluding 2020 and 2021) to develop models for predicting likelihood of angler harvest. Our approach included the development of a global binary classification model using a training data set (70% of records) that included harvest or release as the response variable and a suite of 20 explanatory variables, including fish species or taxa. The model was then applied to a testing data set (30% of records) to measure accuracy. This process was repeated for the 12 most occurring species/taxa in the creel database with all explanatory variables, excluding species/taxa. Variable importance from the global model and summarized variable importance from the species/taxa model were used to quantify factors associated with an angler’s decision to harvest a captured fish. Results The global classification model included 13 of 20 predictor variables for node split determinations, although only combinations of legal harvest status, fish length, and species/taxa were included in the final model. When applied to testing data, we observed accurate classification in 84.3% of records. Species/taxa models displayed considerable variability in included variables. Among the 12 models, 18 of 19 variables were included in node split determinations by the classification algorithms. Model accuracy varied from 67.6% for sunfishes Lepomis spp. to 96.4% for Smallmouth Bass Micropterus dolomieu. Summarized variable importance across all species/taxa models identified fish length and legal harvest status as the most consequential variables influencing fate of captured fish. Conclusions Legal harvest status, fish length, and species/taxa were important determinants of the likelihood of fish harvest in our study. However, some species/taxa (e.g., black basses Micropterus spp.) were infrequently harvested regardless of other associated variables. The interplay between examined factors highlights the importance of understanding social norms associated with fisheries and potential limitations of widespread harvest-based regulations.

ABSTRACT Objective The Missouri River flood of 2011 resulted in the entrainment of Paddlefish Polyodon spathula from above Garrison Dam, a main-stem dam, into the tailrace of the Garrison Reach. A large group of entrained fish (estimated at 3,083 in 2012) remained in the tailrace for several years afterward, not undertaking yearly migrations downriver to Lake Oahe, where feeding and habitat conditions are better. We assessed movements and quantified growth (or weight loss) of individual tailrace Paddlefish from the time of original postflood tagging, as early as 2012 until 2018, and then assessed and quantified upriver movement, growth, maturation, and gonadal fat (energy) reserves of adult Paddlefish following their trap-and-transport repatriation from the Garrison Dam tailrace into Lake Sakakawea and their subsequent recapture upriver in recreational fisheries from 2019 to 2023. Methods Paddlefish were collected with gill nets. Fish were measured for length and weighed at the time of original tagging, in 2018, and upon their subsequent recovery in fisheries. Fish were tagged with individually numbered Monel jaw tags (North Dakota Garrison Reach). Dentary (lower jawbone) sections from harvested fish were collected and aged by established and validated methods. Results Of 57 North Dakota Garrison Reach-tagged fish that were tagged prior to 2018 and recaptured during the 2018 repatriation sampling, 46 fish had lost weight, nine fish had gained weight, one fish showed no change in weight, and one fish lacked adequate weight data. Mean weight dropped from 18.1 kg at original tagging to 15.3 kg in 2018, a highly significant decrease. Subsequently, 12 male and 12 female fish repatriated in 2018 were recaptured in harvest fisheries over the period 2019–2023. Four of the 12 males gained weight, two showed no weight change, and six showed a weight loss. The four males that gained weight each gained more than 0.5 kg/year, whereas only one of the six males that lost weight lost as much as 1.36 kg/year. In contrast, nine females gained weight, one female had no weight change, and two females lost weight. Repatriated Paddlefish participated in spawning-associated movements at similar rates to resident fish. Overall weight gain of repatriated fish was statistically significant for females but not for males. Conclusions Our hypothesis is that imprinting, site fidelity, and evolutionary selection for upriver movement in sexually mature fish played key roles in the observed rigid behavior of the tailrace fish. The break in their familiar life cycle was manifested in the sedentary behavior of tailrace Paddlefish below the dam and their weight loss until repatriation restored their life cycle. Although site fidelity has been found in Paddlefish in several stocks, more research is needed on site fidelity and imprinting for Paddlefish and other native, migratory, nonsalmonid species with life cycles altered by river impoundment.

ABSTRACT Objective Restocking nonnative strains of Brown Trout Salmo trutta into native Marble Trout S. marmoratus habitats has caused hybridization and a demographic decline in wild populations of the endemic species. To address this, genetic characterization of Marble Trout breeders is vital for selecting individuals for reproductive strategies. Integration of genetic analyses with sperm cryopreservation further enhances broodstock quality. Methods In this study, a morphocellular evaluation was conducted to create a live gene bank of breeders for maintaining high-quality offspring production. A total of 229 Marble Trout males from three river basins (Adige, Brenta, and Piave rivers) were sampled at Veneto regional hatcheries in northern Italy. Genetic differentiation among populations was confirmed using a mitochondrial marker (mitochondrial DNA control region [D-loop]) and nuclear markers (lactate dehydrogenase gene LDH-C1* and microsatellites). Fertility parameters, including sperm motility and concentration, were monitored during the reproductive season (November–February) to select high-quality milt for cryopreservation. Results Results showed that 65.49% of samples had high sperm motility throughout the season. Fewer cases of asthenozoospermia occurred mid-season (December–January) compared to the start or end of the season. Average sperm concentration was 14.95 × 10⁹ cells/mL. Conclusions Cryopreserved semen from genetically diverse Marble Trout breeders was used for artificial fertilizations. This combined approach of molecular genetics and innovative cryotechnology supports conservation efforts for Marble Trout and highlights its potential for managing endangered populations effectively.

ABSTRACT Objective Lake elevation decline is a global phenomenon with pronounced effects in arid regions that changes the characteristics of nearshore habitat area available to lacustrine spawners, potentially impacting recruitment and whole-lake food web dynamics. Our objective was to understand the potential effects of lake elevation decline on spawning habitat for the Tui Chub Siphateles bicolor, a lacustrine spawner and critical component of the native food web in Pyramid Lake, Nevada. Methods We explored the distribution of ripe Tui Chub in nearshore habitat by associating habitat characteristics to ripe Tui Chub CPUE from a custom gill-net configuration, with data analyzed using generalized linear mixed-effects models. We then explored potential spawning habitat availability at all potential lake elevations using an elevation-explicit model of the basin that we developed based on several bathymetric and geospatial data sets and the knowledge of spawner distribution gained in the first component of the study. Results Ripe Tui Chub catch was primarily predicted by temperature, reaching a maximum between 14.2°C and 24.8°C found at less than 15 m of depth in Pyramid Lake throughout the summer spawning period. We estimated that with a contemporary decline in lake elevation of 8 m, Pyramid Lake will host the minimum area of spawning habitat based on morphometry alone at a 40% decrease from a theoretical maximum. Conclusions A decrease in lake elevation or an increase in lake temperatures—both of which are probable events based on future climate scenarios and estimates of water extraction upstream of Pyramid Lake—is likely to further restrict Tui Chub spawning habitat area. Our results have important implications for ecological water demand in Pyramid Lake and provide managers with information facilitating a science-based approach to managing the fish community.

ABSTRACT Objective Documenting the effects of hatchery practices on vital rates and abundance of hatchery-origin fish in the wild is important for adaptive management of aquaculture programs aiming to improve the status of wild populations. Here, we synthesize outcomes from a long-running (2001–2021) conservation aquaculture program for White Sturgeon Acipenser transmontanus in the Canada (CDN)–USA transboundary reach of the upper Columbia River. Methods A Bayesian multistate Cormack–Jolly–Seber model was used to estimate abundance, survival, movement, and harvest rates for 14 year-classes of hatchery-origin White Sturgeon. The model was fitted to 20 years of mark–recapture data from more than 140,000 PIT-tagged juveniles released from hatcheries in CDN and the United States between 2001 and 2014. Results There was substantive variation in survival and movement rates among year-classes, which in CDN was driven in part by increased competition from hatchery-origin fish. Survival rates of age-1 fish in CDN declined by fourfold over 7 years during a period when biomass of hatchery fish increased from 0 to 20 kg/ha. Movement rates out of CDN over this period increased by a similar amount. Releasing fish at 30 cm compared to 20 cm led to a fivefold increase in the survival rate to age 5. Age-1 survival rates for fish released in spring or summer were 6- and 27-fold higher compared to survival rates of fish released in fall or winter in CDN and the USA, respectively. Maternal family effects on survival rates were generally weak. Harvest fisheries in the USA reduced the abundance of over-represented year-classes by 44–92% between 2017 and 2021, but the extent of depletions was uncertain due to the limited number of PIT tag recoveries. In 2021, abundance of hatchery-origin fish was 60% higher in CDN (8,900) than in the USA (5,700) due to a combination of (1) higher stocking rates in CDN in the early years of the program and (2) removal of fish in the USA from recreational and tribal fisheries. Conclusions Evaluating the success of sturgeon conservation aquaculture programs requires decades of effort, and adaptive management is challenged by the much shorter time frames that decision makers are used to working with. Our study showed that conservation aquaculture for White Sturgeon in the transboundary reach has achieved some of its original goals in the first two decades of implementation by reducing the risk of extirpation and maintaining genetic diversity of the wild population. High stocking rates during the early years of the program resulted in lower survival of hatchery-origin fish in CDN, higher rates of movement of hatchery-origin fish from CDN to the USA, and lower somatic growth rates of hatchery- and wild-origin fish in both countries. These effects will likely persist for decades owing to the long lifespan of White Sturgeon. Natural spawning of hatchery-origin fish has yet to be documented but will likely begin about three decades after the start of the program. It will take at least four decades from the start of the program to determine whether hatchery-origin fish are increasing natural recruitment to the wild population. Our study underscores the importance of using a rigorous long-term adaptive management framework to evaluate recovery actions and potentially modify them over time.

ABSTRACT Objective The effects of unintentional supplementation from strays from a neighboring conservation supplementation program were evaluated in Nason Creek, a watershed in the Columbia River basin that endangered spring Chinook Salmon Oncorhynchus tshawytscha currently inhabit. Methods We used spawning ground surveys to assess adult age, sex, distribution, abundance, and productivity and a before–after-control–impact design to evaluate the effects of hatchery-origin fish in Nason Creek. Results Adults from hatchery strays made up 14% to 86% (mean = 56%) of the annual spawning escapement in Nason Creek during the unintentional supplementation period. Abundance of total spawners (both hatchery- and natural-origin fish combined) increased by 57% during the period of unintentional supplementation (2001–2016) relative to abundance before large straying events occurred (1981–2000). However, the adult productivity and the abundance of natural-origin spawners that were produced from the supplemented population was nearly halved during the period of unintentional supplementation (2005–2016) and productivity decreased with higher proportions of hatchery-origin spawners. The increases in total spawners were not statistically significantly different from those for reference populations that were not supplemented, but the decreases in natural-origin spawners were significantly different from those for reference streams. Hatchery-origin strays were generally younger (e.g., jacks) and spawned in lower elevations than natural-origin spawners. Conclusions We suggest that abundance of natural-origin spawners was reduced because of a reduction in productivity that was associated with high levels of straying from a neighboring hatchery supplementation program. The reduction may have been from a combination of factors including spawn site selection, age at maturity, hatchery domestication, or density dependence but unlikely from differences from the nearby population in genetics, which were very similar to those of adults in Nason Creek. This study demonstrates that additional hatchery-origin spawners from conservation programs may not increase natural-origin spawners in some populations even when they are very closely related and in low abundance.

ABSTRACT Objective Alewives Alosa pseudoharengus are a culturally, ecologically, and economically important anadromous fish in the northwest Atlantic, yet their movement ecology remains poorly understood. This study was designed to examine mortality events and movement patterns of Alewives, including diel vertical migrations. Methods Using acoustic telemetry, we tagged 32 Alewives during their postspawning migrations through Passamaquoddy Bay (New Brunswick, Canada, and Maine, USA) toward the Bay of Fundy. Generalized additive models (GAMs) were used to examine the spatial distribution and timing of Alewife migrations through the bay. We also used GAMs to investigate occurrences of diel vertical migration in relation to tidal levels. Results Six of the tagged Alewives died during the study, with most mortalities occurring earlier in their migration within the river and estuary habitats, including four cases of endothermic predation: three in the estuary and one in the inner bay. Alewives were predicted to occupy three distinct spatial hot spots over time: the river and estuary during weeks 25–27, the inner bay during weeks 28–30, and the outer bay during weeks 31–32. Regardless of tidal height, the GAMs predicted that Alewives were deeper in the water column during the day (1200–2000 hours) and shallower at night (0200–0700 hours), with intermediate periods used to transition between these depths, indicating that Alewives undertook diel vertical migrations in the marine environment. Conclusions As Alewife populations continue to decline, this research highlights critical aspects of their postspawning movement ecology and underscores the importance of binational and multijurisdictional cooperation in the effective management of this species.