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Accurate and precise estimates of survey abundance indices are essential inputs for stock assessment models and are important for the successful conservation and management of fisheries stocks. Since abundance indices can be standardized in various different ways, from conventional design-based approaches to model-based approaches, it is essential to compare the efficiency of those approaches and quantify the consequences for stock assessments. In this study, we focus on an important commercial stock of witch flounder (Glyptocephalus cynoglossus) in NAFO 3N+3O divisions. We first compare the survey indices standardized by design-based and model-based approaches, and find that a model-based estimator provides more precise estimates of survey indices than design-based approach for this stock. We then apply a widely used age-structured statistical catch-at-length (ACL) assessment model to the standardized catch-at-length survey indices from both approaches to estimate the age-based population dynamics for this stock. We conclude that the ACL model fit to model-based indices performed better than the same model fit to design-based indices. [ABSTRACT FROM AUTHOR]

The impoundment of the Yangtze River and construction of the Three Gorges Dam and Reservoir created an unnatural flow regime with a 30 m water-level fluctuation and four artificial seasons that differ from the river's natural flow-regime timing. Using stable isotopes, we selected 15 common benthic fish species representing five trophic guilds to analyze seasonal variation in production sources, trophic niche width, and niche overlap. We hypothesized that, similarly to a natural flow regime, artificial hydrological seasons effectively influence fish trophic niches. We found consistency in seasonal shifts in the contribution of aquatic and terrestrial producers to fish biomass. δ13C and δ15N depicted seasonal changes in intra-guild trophic niche width and intra- and inter-guild niche overlap. Considering that the Three Gorges Reservoir's flow regime is artificially regulated, our findings suggest that water-level fluctuation is one of the key mechanisms driving such trophic shifts and allowing multiple species to coexist. Given the increased cascaded large reservoir construction and the concomitant creation of unnatural flow regimes in large rivers worldwide, these findings are timely. Our findings contribute to improving water-level management by optimizing rhythmicity while balancing flood control and fish protection. [ABSTRACT FROM AUTHOR]

Population abundance is a critical metric in fisheries and conservation, but it is very difficult to measure accurately. Existing estimation methods present significant challenges: mark–recapture methods are time- and labour-intensive, and hydroacoustic echo counting methods face issues with target identity and the habitat types where they can be effectively applied. We present a new methodology for abundance estimation that can improve the reliability of echo counting methods. Split beam hydroacoustic survey data are integrated with telemetry data from fish bearing acoustic transponder tags. These tags are counted by a spatially and temporally concurrent multibeam acoustic survey to produce mark–recapture abundance estimates. We assessed this approach on four wild lake trout populations, ranging in abundance from ∼200 to ∼3000 adults. Our abundance estimates were consistent with those derived from conventional Schnabel and Jolly–Seber mark–recapture studies. We show that the precision achievable with this method in 1 year of field work rivals that provided by long-term (>10 years) continuous mark–recapture studies. We also discuss other ecological questions that could be addressed with this approach. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) monitoring methods have played a significant role in improving fisheries management decisions. Yet, their impact to date has been rather limited in Canada, where eDNA sampling and analyses are only beginning to be used to inform management and conservation decisions, practices, and policies. Studies investigating hurdles to the incorporation of eDNA evidence into fisheries management decisions generally focus on technical challenges (i.e., risks of false-positive and false-negative detections). We set out to identify challenges that eDNA researchers and conservation practitioners must overcome to fully unlock the benefits of eDNA sampling for fish management in the Canadian context. We discuss aspects of the broad and heterogeneous geography, preponderance of regions located far from densely populated areas, complex political landscape, and cultural diversity of Canada that may complicate the design of reliable eDNA monitoring tools or restrict their use if not adequately addressed. To advocate for the wider use of eDNA sampling, we outline a number of action items that would facilitate the broad adoption of eDNA sampling as a monitoring tool at the Canadian scale. [ABSTRACT FROM AUTHOR]

Ecological forecasts are potentially of great value for managing fisheries and for stakeholders dependent on their long-term sustainability. Yet, most forecasting approaches are data-intensive, requiring information not just on the focal species but also on ecological interactions and the physical environment. Empirical dynamic modeling (EDM) is an equation-free approach to forecasting species' abundance using only data on past abundance, but the time series required for this approach must be long enough to reconstruct the dynamics of the system. This requirement is rarely met, especially for long-lived species. Here we used simulations and empirical data to demonstrate that incorporating time series from multiple age classes can improve our ability to forecast abundance compared to a single age class or index of total abundance. Including data from multiple age classes produced the greatest gains in forecast accuracy when time series were the shortest. Overall, our results show that the incorporation of age structure could allow EDM to be applied to many species for which relatively short time series would have previously been a limiting factor. [ABSTRACT FROM AUTHOR]

In recent decades, chum salmon (Oncorhynchus keta) on the Central and North Coasts of British Columbia have experienced increasing variability and declining abundance. Chum are targeted by mixed-stock commercial fisheries despite declining trends and limited stock assessment to clarify conservation and fishery tradeoffs. We analyzed trends in chum salmon run sizes to 25 watersheds in the Central Coast region, to support co-governance of fisheries under newly ratified Fisheries Resources Reconciliation Agreement. Central Coast chum have declined by ∼90% since 1960, and only three populations did not undergo an evident decline. Bella Coola enhanced chum had an increasing trend but have experienced 29-fold variation in run sizes since 2005. Recently, Bella Coola enhanced chum comprised over 50% of Central Coast chum abundance and the contribution of this stock to overall abundance has more than tripled (from 13.8%) since enhancement began. Given concerns about the long-term health of chum salmon stocks and the social–ecological systems they support, commercial fisheries were closed on the Central Coast in 2021. If current trends continue, fishery opportunities may remain limited. [ABSTRACT FROM AUTHOR]

Accurate estimates of abundance are a cornerstone for resource managers to make effective decisions for fish conservation. However, multiple sampling methods often are required to sample fish communities, and ignoring the detection process can create substantial bias in latent state parameter estimation (e.g., abundance, survival). We developed a joint-species N-mixture model that integrated snorkel, seining, and electrofishing surveys to estimate factors affecting native and non-native fish distributions in the Santa Ana River, California. We found through data integration that native Santa Ana sucker (Catostomus santaanae) and arroyo chub (Gila orcuttii) were most abundant in wide stream channels, and the abundance of both native fishes were negatively correlated with non-native largemouth bass (Micropterus salmoides). Our results highlight the power of integrating multiple data sets into a single analysis and incorporating among-species correlation into abundance modeling. Our results also highlight a pattern of native fish declines that coincides with an expanding largemouth bass population, a concern for the management of native aquatic communities within the Santa Ana River. [ABSTRACT FROM AUTHOR]

Management of mixed-stock Chinook salmon (Oncorhynchus tshawytscha) fisheries requires balancing fishery access and conservation of vulnerable stocks. Although accurate, timely estimates of stock-specific harvest are crucial in achieving competing objectives, limited numbers of stock assignments (e.g., tag recoveries) can diminish the utility of estimates. We used a flexible simulation approach, applied to both a theoretical and real-world fishery case study, to compare the performance of competing monitoring alternatives and estimators for harvest. We sought to improve accuracy for point estimates of harvest and harvest trajectories over time. Bayesian models provided similarly accurate point estimates to existing models at high levels of data aggregation, generally improved estimates of harvest trajectories at intermediate aggregation, and reliable estimates of uncertainty. Incorporation of time-lagged prior information inconsistently improved estimates of harvest trajectories. Among monitoring alternatives yielding equal increases (33%) in coded wire tag recoveries, increasing tagging rates resulted in the greatest decrease in estimate uncertainty for target stocks (37.5% to 45.3%). Variable performances of mixed-stock harvest estimators suggest their use should considered on a stock- and fishery-specific basis, potentially using a simulation-based approach. [ABSTRACT FROM AUTHOR]

Temperate zone winters are experiencing greater rates of warming relative to other seasons and latitudinal regions globally. Spring-spawning fishes native to northern environments rely on both increasing temperature and lengthening photoperiod to cue reproduction and may thus be particularly sensitive to rapid warming earlier in the year while day lengths remain short. We investigated the reproductive response of pumpkinseed sunfish (Lepomis gibbosus) to spring warming commencing at a range of day lengths (9–15 hours), corresponding to various calendar days (10 January – 22 May). In both the laboratory and field, both male and female fish that experienced early warming while day lengths were <11 hours (1) failed to initiate reproductive preparation in the liver before gonad development began and (2) had reduced reproductive allocation. Analysis of published data on temperate fishes suggested that liver development prior to gonad development is widespread across warm-, cool-, and cold-water thermal guilds, though the precise phenology of liver relative to gonad development appears to vary widely among species. Together, our results point toward dampened reproductive preparation as a novel mechanism mediating reduced reproductive output in both warm- and cool-water fish following earlier spring warming. [ABSTRACT FROM AUTHOR]

Identifying how habitat structure influences the spatiotemporal movements of fishes is important for conservation, population assessment, and management purposes. Here, we determined whether acoustically tagged lake trout (Salvelinus namaycush) from a 305 ha lake exhibited homing behaviour and lake basin fidelity over multiple seasons and years. The lake has two distinct deep basins (north and south) connected by a shallower centre basin. Fifteen lake trout captured during the spawning season from both deep basins were tagged and released in the south basin. All translocated north-basin fish quickly returned to the north basin (median = 1.85 days, range = 0.36–4.5 days), apart from one fish that returned 41 days post-release, while none from the south ventured into the north basin during this time. After translocated individuals returned, all fish demonstrated high basin fidelity among years, as >90% of detections were from the same basin fish were captured, while <0.7% (by three fish) were from the opposite deep basin and <9% from the centre basin. The probability a fish was detected outside its basin of capture was highest in winter (15.9%) and fall (14.3%) and lowest in summer (0.41%). [ABSTRACT FROM AUTHOR]

Quantifying the scale of offspring dispersal is essential for understanding demographic connectivity across landscapes and rates of population spread. However, characterizing natal dispersal in fishes is complicated by the difficulties of tracking origins and movement during early life-history stages. We combined direct observation of natal dispersal based on otolith chemistry with indirect estimates of dispersal from population genetics to quantify intergenerational dispersal of smallmouth bass (Micropterus dolomieu) inhabiting a river network. Average parent–offspring dispersal was estimated as 7.7 km from genetic isolation-by-distance and demographic population data. Otolith chemistry indicated that adults were captured an average of 8.3 km from their natal tributary, supporting the genetics-based estimate. Our estimate of intergenerational dispersal is higher than previous estimates for lotic fishes and considerably higher than estimates for smallmouth bass in lake systems. Differences in availability of seasonal habitats for smallmouth bass may account for the contrasting scales of dispersal between lake and river populations. The large intergenerational dispersal distance of riverine smallmouth bass should be considered in conservation of fisheries or efforts to control invasive populations in river networks. [ABSTRACT FROM AUTHOR]

The Magnuson–Stevens Fishery Conservation and Management Act mandates US fisheries minimize adverse effects of fishing on essential fish habitat (EFH). The Gulf of Maine (GoM) American lobster (Homarus americanus) fishery is the most valuable US fishery and can deploy more than three million traps annually. To date, the impact of this fishery on benthic EFH has not been addressed quantitatively. To evaluate the impact of the GoM lobster fishery on EFH, we incorporated lobster fishing effort into a model linking habitat susceptibility and recovery to area impacted by fishing gear: the Swept Area Seabed Impact model. Impact to EFH was localized along the coast and highest along midcoast Maine. Upwards of 13% of the benthos is in the process of recovery, but between 99.92% and 99.96% of initially affected habitat fully recovers. These estimates suggest that lobster fishing negligibly contributes to accumulation of EFH damage in the GoM due to the expansive area fished and the small footprint of each trap. Identifying areas of persistent impact is crucial in developing effective fisheries management for critical marine habitats. [ABSTRACT FROM AUTHOR]

The performance indicator isthecorrectidentificationrate: d9Th correctidentificationrate ¼ number of years the stock status is correctly identified total number of years the stock status is identified 100% 2.2.Simulation2:evaluatingtheMPs Gcontrol is an MP that solely relies on slope S/B to identify the stock status and recommend catch limits accordingly. Performancemeasures The performance of a stock status identification approach is quantified by comparing the identified stock status from each approach with the true stock status. ARTICLE Comparingasuiteofsurplus-production-basedstockstatus identificationapproachesandmanagementprocedures LuoliangXu,CameronHodgdon,MingSun,MackenzieMazur,XinjunChen,andYongChen Abstract:Different approaches have been used to identifyfishery stock status when only biomass and catch data are available. [Extracted from the article]

Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial–thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized linear mixed effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (∼480%) once trout suppression surpassed ∼60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery. [ABSTRACT FROM AUTHOR]

Accounting for population diversity can be critical to the sustainable management of mixed-stock fisheries because harvest rates that can be sustained by productive populations may come at the cost of overfishing less productive ones. While these harvest–diversity trade-offs are well-recognized, their consequences for harvest policy performance are not often explicitly evaluated in contemporary fisheries management. We use closed-loop simulations to evaluate the ability of alternative harvest policies to meet population diversity and fishery objectives for one of the largest subsistence Chinook salmon (Oncorhynchus tshawytscha) fisheries in the world (Kuskokwim River Basin in western Alaska). We found clear evidence of population diversity that resulted in asymmetric trade-offs among fishery and conservation objectives whereby policies that forgo relatively small amounts of harvest result in relatively large increases in equitable access to Chinook and elimination of risk of weak stock extirpation. The performance of alternative harvest policies, and the magnitude of trade-offs, were sensitive to regime shifts and uncertainty in the drivers of recruitment variation. However, we found that harvest policies that prioritized meeting minimum subsistence needs were unlikely to jeopardize long-term sustainability. [ABSTRACT FROM AUTHOR]

Most fishery regulations aim to control angler harvest. Yet, we lack a basic understanding of what actually determines the angler's decision to harvest or release fish caught. We used XGBoost, a machine learning algorithm, to develop a predictive angler harvest–release model by taking advantage of an extensive recreational fishery data set (24 water bodies, 9 years, and 193 523 fish). We were able to successfully predict the harvest–release outcome for 99% of fish caught in the training data set and 96% of fish caught in the test data set. Unsuccessful predictions were mostly attributed to predicting harvest of fish that were released. Fish length was the most essential feature examined for predicting angler harvest. Other important predictive harvest–release features included the number of individuals of the same species caught, geographic location of an angler's residence, distance traveled, and time spent fishing. The XGBoost algorithm was able to effectively predict the harvest–release decision and revealed hidden and intricate relationships that are often unaccounted for with classical analysis techniques. Exposing and accounting for these angler–fish intricacies is critical for fisheries conservation and management. [ABSTRACT FROM AUTHOR]

The specificity and accuracy of inferred fish origin and movement relies on describing spatial heterogeneity and temporal stability of environmental signatures. But the cost and logistics of sample collection often precludes the complete quantification of environmental signature temporal stability and spatial heterogeneity. We used repeated sampling and a novel approach (Bayesian ridge regression, BRR) to quantify the temporal stability and spatial heterogeneity of 87Sr/86Sr, respectively. We explained 86% of observed variation in 87Sr/86Sr using a BRR model and estimated 87Sr/86Sr throughout the Upper North Platte River Basin with high accuracy (±0.00106). Year to year variation in 87Sr/86Sr signatures ranged from 0.00007 to 0.00073 (SD), while seasonal variation ranged from 0.00091 to 0.00134 (SD). We then assessed the specificity and discussed the accuracy of inferring movement using three scenarios of described spatial heterogeneity. Our results indicate reliable inference of fish movement requires comprehensive quantification of spatial heterogeneity and temporal variation in environmental signatures. [ABSTRACT FROM AUTHOR]

Taylor's power law (TPL), which states that the variance of abundance is a power function of mean abundance, has been used to design sampling of agricultural pests and fish species. We show that TPL holds for means and variances of abundance of accumulated fish samples in the fished and unfished areas separately of Lake Kariba (between Zambia and Zimbabwe), measuring abundance indices by number and weight separately. We use TPL parameters estimated from sequentially accumulated samples to update a stopping line of fixed precision 0.1 after each new sample from a sampling day. In these Lake Kariba data, depending on the sampling area and abundance measure, our updated stopping-line method requires 21% to 41% of the number of sampling days and 19% to 40% of the number of samples that are planned a priori and performed under systematic sampling. Our novel method yields mean abundance estimates similar to those from systematic sampling and provides a conservative approach to reaching a fixed sampling precision level with reduced sampling labor and time. Using mixed-effect modeling for cumulative means and variances with either number or weight from both fished and unfished areas, we find that fishing increases the slope of TPL. This study provides the conceptual framework and an empirical case study for implementing a sequential sampling method for fish assemblages of an inland lake. The possible limitations and applications of our method for sampling in other environments are discussed. [ABSTRACT FROM AUTHOR]

Telemetry studies have produced fundamental knowledge on animal biology and ecology that has the potential to improve management of aquatic resources such as fisheries. However, the use and integration of telemetry-derived knowledge into practice remain tenuous, so we surveyed 212 fish telemetry experts to understand existing barriers for incorporating telemetry-derived knowledge into fisheries management practices. We apply a sociological knowledge–action framework to structure the findings, which revealed four primary challenges to integrating telemetry findings into management: (1) the perceived uncertainties and unclear relevance of telemetry findings; (2) the underlying motivations and constrained rationalities of actors that can lead to inaction or suboptimal decisions; (3) the constraints of institutions, governance structures, and lack of organizational support, and (4) time and mismatches in scale, culture, and world views. On a more positive note, the relational dimension (collaboration, trust, and relationship building) appears to be important for overcoming and avoiding barriers. We further provide recommendations to navigate these perceived barriers and argue that these lessons also apply to other fields of applied ecology, conservation, and resource management. [ABSTRACT FROM AUTHOR]

Examination of the genetic basis of the timing of the return migration of Atlantic salmon (Salmo salar) to fresh water from the sea, a trait of economic and conservation interest, was carried out using a genome-wide association study. We examined genotype data of 52 731 single nucleotide polymorphic (SNP) markers from 73 early and 49 late running two-sea-winter salmon from five rivers in eastern Scotland. A single region of the Atlantic salmon chromosome Ssa09 was identified, containing nine SNP markers significantly associated with run timing, a region previously linked to variation in sea age at maturity. Validation of the markers in a group of 233 one- and two-sea-winter fish, including adults from a novel river, again showed significant associations between the trait and the Ssa09 region, explaining ∼24% of the trait variance. The SNP loci identified provide the ability to examine trait variation in populations of Atlantic salmon and so help facilitate conservation management of the differing run timing phenotypes. [ABSTRACT FROM AUTHOR]

Hatchery supplementation has been developed to conserve salmonid populations and provide fisheries. We evaluated supplemented and reference Chinook salmon (Oncorhynchus tshawytscha) populations prior to, during, and after supplementation ceased for 22 years in two major drainages in Idaho, USA. Basin-level analyses showed supplementation increased abundance at some life stages, but effects did not persist into the postsupplementation phase and had no apparent influence on productivity. Natural-origin juvenile abundance increased during supplementation but results for adults were ambiguous. After supplementation ceased, abundance and productivity in supplemented and reference populations returned to their presupplementation relationships. Intensive analyses of supplemented populations with weirs showed abundance increased at some life stages with the addition of female spawners. However, the rate of increase varied with female origin (natural > supplementation ≥ nontreatment hatchery), and effects diminished through the life cycle. Based on these findings, we provide guidance for conservation programs. Supplementation alone is not a panacea because it does not correct limiting factors, which must be addressed to achieve population levels capable of sustaining ecological function and harvest. [ABSTRACT FROM AUTHOR]

Larval drift and dispersal are critical processes that affect recruitment success for many riverine fishes. Hypolimnetic discharge from the Three Gorges Dam (TGD) lowers river temperature and reduces downstream nutrients, inducing distinct shifts in habitat conditions downstream of the dam. The inflow of major tributaries buffers these influences and creates physiochemical gradients according to the distance from the dam. We investigated the abundance, feeding, and growth of larvae of four major Chinese carps in three sections of the middle Yangtze River. Water temperature and transparency showed clear spatial gradients. Larvae in the river section closest to the dam tended to be lower in abundance and temporally delayed peak abundance and showed lower feeding intensity, poorer condition, and slower growth than those further from the dam. Our results demonstrate that physiochemical gradients influenced by the TGD have strong effects on abundance, feeding, and growth of the drifting larvae. We recommend that river sections farther from the TGD, particularly around the mouth of Poyang Lake, should become high-priority conservation areas to enhance protection of critical aquatic species. [ABSTRACT FROM AUTHOR]

The Atlantic wolffish ( Anarhichas lupus) is listed by Canada's Species at Risk Act as a species of special concern. Effective conservation strategies rely on accurate knowledge of habitat requirements, distribution, and vulnerabilities; however, current management plans cite lack of wolffish habitat data as a key limitation. For this study, coastal Atlantic wolffish denning habitat was characterized and mapped with high-resolution multibeam data and seafloor video in Conception Bay, Newfoundland. Four Atlantic wolffish dens, used for feeding, spawning, and egg-guarding, were surveyed and mapped. On the basis of the geomorphology and substrate of these dens, a supervised classification was applied to the multibeam bathymetry and backscatter data to identify other potential denning areas. Predicted denning habitat, limited by the occurrence of suitable rocky substrate, is most prevalent in shallow waters (<22 m) distributed over 1.6 km2 (5.9%) of the study area. Shallow denning habitat is exposed to seasonal maximum temperatures that exceed the threshold for normal Atlantic wolffish egg development, a potential vulnerability for nearshore wolffish. As management efforts progress, this information will guide research and prioritization of conservation areas. [ABSTRACT FROM AUTHOR]

Simulation is used to explore the effect of spatial heterogeneity and spatial closures on the ability of feedback-control management strategies to achieve goals relating to conservation and utilization of fishery resources. The operating model underlying the projections is based on pink ling, Genypterus blacodes, off southern Australia and assumes that animals are sedentary following settlement. The management strategies are able to move the resource towards the target level in the absence of spatial closures even though assessment results are biased. The probability of reducing the stock below its limit reference point is higher when growth rates vary spatially, but the effect is small. The probability of the stock being above its target reference point is lower when one of the smaller spatial areas is closed. However, performance is markedly different when a larger fraction of the total area is closed, with stock size being substantially larger than the target at the end of the projection period. [ABSTRACT FROM AUTHOR]

Canada's Policy for Conservation of Wild Pacific Salmon has been heralded as a transformative approach to the management of wild salmon whereby conservation is the highest priority. Given that changes to the Policy are under consideration, it is timely that we understand whether our state of knowledge and the status of wild salmon in Canada have indeed improved after its adoption in 2005. To answer these questions, we used two indices of improvement: ( i) monitoring effort and ( ii) abundance of spawning adults. Our results, based on data for all species from British Columbia's north and central coasts, show that monitoring effort has continued to erode, abundance of spawning adults has significantly declined for several species, the status of many salmon Conservation Units are in zones of concern, and 42% of the Conservation Units that we assessed as Red (threatened) would have improved in status had the Canadian fishery been reduced. We conclude with recommendations to help improve our knowledge of the status of salmon and enable a robust and successfully implemented Wild Salmon Policy for the future. [ABSTRACT FROM AUTHOR]

Knowing the species and life stages of prey that predators consume is important for understanding the impacts that predation may have on prey populations, but traditional methods for determining diets often cannot provide sufficient detail. We combined data from two methods of scat analysis (DNA metabarcoding and morphological prey ID) to quantify the species and life stages of salmon ( Oncorhynchus spp.) consumed by harbour seals ( Phoca vitulina) in the Strait of Georgia, Canada, where juvenile Chinook ( Oncorhynchus tshawytscha) and coho ( Oncorhynchus kisutch) salmon survival is poor. Harbour seals primarily consumed adult salmon of lesser conservation concern in the fall (August-November): chum ( Oncorhynchus keta: 18.4%), pink ( Oncorhynchus gorbuscha: 12.6%), sockeye ( Oncorhynchus nerka: 7.4%), Chinook (7.1%), and coho (1.8%). However, the opposite species trend occurred during the spring when seals preferred juvenile salmon of greater conservation concern (April-July): coho (2.9%), Chinook (2.9%), sockeye (2.5%), pink (1.4%), and chum (0.8%) - percentages that can equate to many individuals consumed. Our data suggest that harbour seals select juveniles of salmon species that out-migrate at ages >1 year and provide evidence of a potential causal relationship between harbour seal predation and juvenile salmon survival trends. [ABSTRACT FROM AUTHOR]

Conservation of stream fishes requires an understanding of how their reproduction and recruitment are affected by environmental conditions. Flow regulation and habitat loss in North American Great Plains streams threaten many native fishes, including pelagic-broadcast spawning cyprinids. Pelagic-broadcast spawning by flathead chub ( Platygobio gracilis), a species declining throughout much of its extensive range, began after temperatures exceeded 15 °C in Fountain Creek, Colorado (USA), despite different annual flows. Alternatively, streamflow patterns controlled recruitment of juveniles because high-magnitude summer flows (spikes) reduced abundance of larvae hatched just prior to or during such events. Juvenile recruitment was highest for larvae hatched just after summer flow spikes occurred or during stable base flow periods. Understanding environmental conditions suitable for reproduction as well as subsequent recruitment should inform conservation actions, especially in flow-altered streams, and improve prospects for persistence of imperiled Great Plains cyprinids, including flathead chub. [ABSTRACT FROM AUTHOR]

Fish habitat is essential to the stability and productivity of fisheries. In Canada, the primary legal tool for protecting fish habitat is the federal Fisheries Act. In 2012, this law was changed to narrow the scope of habitat protection. The government's position was that the previous regime went beyond what was necessary to protect fish and fish habitat. Here, we tested that assertion by examining Fisheries Act authorizations to harmfully alter, disrupt, or destroy fish habitat issued by Fisheries and Oceans Canada during a 6-month period in 2012, obtained using access to information processes. We found the majority of projects (67%) were authorized to impact more habitat than proponents were required to compensate for, likely resulting in a net loss of fish habitat. Our analysis show an aggregate net loss - defined as authorized impact minus required compensation - of 2 919 143 m2 authorized across 78 projects. Drawing from these results, we present four recommendations for an improved habitat protection regime under a renewed Fisheries Act, emphasizing the need to establish a public registry for authorizations and monitoring data. [ABSTRACT FROM AUTHOR]

Population size estimates for stream fishes are important for conservation and management, but sampling costs limit the extent of most estimates to small portions of river networks that encompass 100s-10 000s of linear kilometres. However, the advent of large fish density data sets, spatial-stream-network (SSN) models that benefit from nonindependence among samples, and national geospatial database frameworks for streams provide the components to create a broadly scalable approach to population estimation. We demonstrate such an approach with density surveys for trout species from 108 sites in a 735 km river network. Universal kriging was used to predict a continuous map of densities among survey locations, and block kriging (BK) was used to summarize discrete map areas and make population estimates at stream, river, and network scales. The SSN models also accommodate covariates, which facilitates hypothesis testing and provides insights about factors affecting patterns of abundance. The SSN-BK population estimator can be applied using free software and geospatial resources to develop valuable information at low cost from many existing fisheries data sets. [ABSTRACT FROM AUTHOR]

To effectively conserve and restore stream ecosystems, we need to better understand the distribution and abundance of individual fish species in relation to natural environments and anthropological stressors. In this study, we modeled the abundance of 97 fish species in small wadeable streams of Illinois, USA, based on random forests regression and landscape-level environmental variables. Model R2 values for intermediately common species were higher than for common species, but highly variable among rare ones. Models for 50 species reached R2 of 0.2-0.70 and were tested with a separate set of samples and applied to unsampled wadeable reaches to show the population hotspots of each species across the state. Furthermore, we evaluated the importance of individual environmental variables to a given fish species as well as the directional responses of each species to top 10 key predictors. Climate and land use were the best predictors for most species, followed by topography, geology, and soil permeability. Spatial connection of a stream also was associated with a large number of species. These findings improved our understanding of the relationships between fish species and landscape environments. The distribution maps could guide resource management, restoration, and monitoring of stream fish assemblages. [ABSTRACT FROM AUTHOR]

Bycatch of mid-trophic-level anadromous fishes that connect marine and freshwater ecosystems is a growing conservation concern. Anadromous alewife ( Alosa pseudoharengus) and blueback herring ( Alosa aestivalis) are important components of coastal freshwater and marine food webs, but have experienced dramatic declines in the abundances of spawning adults. Freshwater-focused restoration efforts have yielded few consistent signs of recovery, raising concerns that bycatch in Northwest Atlantic commercial fisheries may be negating these conservation actions. Using data from 15 microsatellites genotyped for baseline populations and bycatch, we conducted genetic stock identification to understand how bycatch was partitioned among previously identified regional genetic stocks. We then combined this information with fishery observer data to estimate genetic stock-specific bycatch mortality for the southern New England Atlantic herring fishery (2012-2013). Bycatch overall, but especially in the Atlantic herring fishery, was disproportionately assigned to the most severely depleted genetic stocks (alewife southern New England stock - 70% of assignments; blueback herring mid-Atlantic stock - 78% of assignments). These genetic stocks overlap in the region surrounding Long Island Sound, suggesting that bycatch taken from this area in recent years may be negatively impacting recovery efforts in this region. Our study suggests that mitigating bycatch on the southern New England fishing grounds may benefit recovery efforts for alewife and blueback herring genetic stocks that have experienced the greatest declines in spawning adult abundances. [ABSTRACT FROM AUTHOR]

Detecting and determining changes in the occurrence and abundance of species is a priority for effective management of resources and for conservation of biodiversity. In the absence of long-term monitoring data, potential population declines may be very difficult to establish. Therefore, alternative information on occurrence of species to infer population trends is highly valued. Records of sharks (i.e., Notorynchus cepedianus, Carcharias taurus, Galeorhinus galeus, and Carcharhinus brachyurus) off northern Argentina from a recreational fishing magazine (Weekend), between 1973 and 2008, were reviewed with the aim of evaluating population trends with opportunistic data sources. For each shark species, the number of occurrences per year in the magazine was registered. Our analyses were based on a nonprobabilistic method (McPherson and Myers' approach) designed to determine population trends with opportunistic sighting records. In this approach we included the number of classified ads offering fishing guide services published per year in the magazine as a measure of observation effort. For each species, we fitted generalized linear models with a Poisson error structure and a log link, where the response variable was the number of occurrences per year, the explanatory variable was the year, and the logarithm of the number of fishing guide ads was specified as an offset in each model. For both approaches, the models estimated that populations of the four shark species have suffered declines. Estimates produced by these models will help to determine the magnitude of population changes where a paucity of data prevents more precise analysis. [ABSTRACT FROM AUTHOR]

Changes in density-independent mortality can alter the spatial extent of populations through patch extinction and colonization, and spatial contraction may alter population productivity and compensatory capacity. Here, we analyze a time series of steelhead ( Oncorhynchus mykiss) abundance and examine the hypothesis that spatial contraction can decrease compensatory capacity. Over the last 20 years, steelhead in the Keogh River have declined by an order of magnitude because of a period of poor smolt-to-adult survival. Low abundance has been associated with more depressed production of out-migrating smolts than would be expected based on traditional models of compensatory dynamics. Patterns of juvenile density over time show changes in the spatial distribution of the population. We developed a spatially explicit population model to explore spatial structure and juvenile recruitment under varying marine survival. Results suggest that spatial contraction during a period of poor marine survival can strengthen density-dependent population regulation, reducing smolt production at the watershed scale. Our results highlight that spatial contraction can alter the fundamental density-dependent relationships that define population dynamics, recovery trajectories, and sustainable harvest levels of spatially structured populations. [ABSTRACT FROM AUTHOR]

The development of effective nonlethal biomonitoring techniques is imperative for the preservation of imperiled freshwater mussel populations. Changes in hemolymph chemistry profiles and tissue glycogen are potential biomarkers for nonlethally monitoring stress in mussels. We sampled three species in the Flint River Basin over 2 years to evaluate how these hemolymph and tissue biomarkers responded to environmental changes. We used hierarchical linear models to evaluate the relationships between variation in the biomarkers and environmental factors and found that the responses of the hemolymph and tissue parameters were strongly related to stream discharge. Shifts in alanine aminotransferase and glycogen showed the largest relations with discharge at the time of sampling, while magnesium levels were most explained by the discharge for 5 days prior to sampling. Aspartate aminotransferase, bicarbonate, and calcium showed the strongest relations with mean discharge for 15 days prior to sampling. The modeling results indicated that biomarker responses varied substantially among individuals of different size, sex, and species and illustrated the value of hierarchical modeling techniques to account for the inherent complexity of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The northern Dolly Varden ( Salvelinus malma malma) displays variable life-history types and occupies freshwater habitats with varying levels of connectivity. Here, we assayed microsatellite DNA variation in northern Dolly Varden from the western Canadian Arctic to resolve landscape and life-history variables driving variation in genetic diversity and population structure. Overall, genetic variation was highest in anadromous populations and lowest in those isolated above waterfalls, with stream-resident forms intermediate between the two. Anadromous and isolated populations were genetically divergent from each other, while no genetic differentiation was detectable between sympatric anadromous and stream-resident forms. Population structure was stable over 25 years, hierarchically organized, and conformed to an isolation-by-distance pattern, but stream-isolated forms often deviated from these patterns. Gene flow occurred primarily among Yukon North Slope populations and between sympatric anadromous and resident forms. These results were sex-dependent to some extent, but were influenced more by reproductive status and life history. Our study provides novel insights into the life history, population demographic, and habitat variables that shape the distribution of genetic variation and population structure in Arctic fluvial habitats while providing a spatial context for management and conservation. [ABSTRACT FROM AUTHOR]

Recognizing the mechanisms by which environmental conditions drive population dynamics can greatly benefit conservation and management. For example, reductions in densities of spawning Pacific salmon ( Oncorhynchus spp.) have received considerable attention, but the role of habitat characteristics on population sizes of breeding salmon is not fully understood. We studied relationships between habitat characteristics and stream population densities of spawning chum ( Oncorhynchus keta) and pink ( Oncorhynchus gorbuscha) salmon in 44 streams in the Great Bear Rainforest of coastal British Columbia, Canada, with individual streams as the unit of comparison. Our results indicate that a small number of habitat characteristics are important in predicting population density of spawning chum and pink salmon in streams, namely pH for chum salmon and riparian slope and large wood volume for pink salmon. This is the largest multivariable comparison to examine habitat-population relationships in adult spawning salmon and may provide useful quantitative emphasis in guiding management. [ABSTRACT FROM AUTHOR]

Marine conservation is often perceived as being in conflict with fisheries management. In Canada, at-risk marine fishes denied listing under the Species at Risk Act (SARA) are meant to receive comparable measures under the Fisheries Act. We assess the effectiveness of these Acts by examining ( i) how long it takes a marine fish assessed as being at risk to move through the process and receive conservation measures, ( ii) whether there are biases against marine fishes in the SARA process additional to the known listing bias, and ( iii) when denied listing, to what extent these species are protected by the Fisheries Act. Overall, at-risk marine fishes typically spend 3.25 years under consideration for SARA, during which time they receive no additional protection. Endangered and Threatened marine fishes (i.e., those most at risk) face the greatest bias and receive the least protection; their SARA decisions are typically delayed, with almost 5 years usually passing between their COSEWIC (Committee on the Status of Endangered Wildlife in Canada) assessment and listing decision; most (70.6%) are then denied listing, after which the Fisheries Act provides few of the SARA-required measures. For SARA-listed marine fishes, recovery strategies are usually late and to date no action plans have been produced. Marine fish conservation is hindered by SARA's slow pace, incomplete recovery measures, and inadequate implementation of the Fisheries Act. We provide recommendations for improving conservation of at-risk marine fishes in Canada. [ABSTRACT FROM AUTHOR]

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A weight-of-evidence evaluation of the potential cause of white sturgeon ( Acipenser transmontanus) recruitment failure in the upper Columbia River evaluated 12 recruitment-failure hypotheses based on nine criteria. Recruitment-failure timing was estimated by identifying breakpoints in the hindcasted recruitment time series for three of four spatially distinct groups. Observed spatial and temporal recruitment decline patterns were then compared with expected patterns for each hypothesis (e.g., flow, temperature, turbidity, contaminants, and changes to the riverine fish community). The weight-of-evidence evaluation also considered criteria including coherence with theoretical, factual, and biological evidence and responses to impact reversal. Recruitment failure began about 1968, coincident with the initiation of upstream mainstem flow regulation. An 8- or 9-year lag in the recruitment decline of the Waneta group was particularly informative for hypothesis evaluations. The identification of increased fine substrates at spawning sites as the most plausible explanation for chronic recruitment failure has important implications regarding the apparent life stages affected and potential restoration approaches. [ABSTRACT FROM AUTHOR]

The abundance of alewife ( Alosa pseudoharengus) and blueback herring ( Alosa aestivalis) has declined throughout their range, and there are increasing concerns about their conservation status. Because of their diadromous life history, variability in rates of survival in fresh water can affect overall recruitment. The objective of our study was to assess how river temperature and flow influence young of the year (YOY) river herring recruitment in the Northeast US. Observations of adult and juvenile fish in five rivers were used to construct spawner-YOY recruits models; these rivers were chosen because of the length of the time series (>15 years) and the paired observations of spawners and juveniles. An environmentally explicit stock-recruitment model explained a substantial fraction (41% to 80%) of the variance in YOY abundance, depending on river system. Our approach allowed for a preliminary discussion of potential mechanisms, which need to be further substantiated by focused field and laboratory studies. Early summer river flow and river temperature had the greatest influence, indicating the importance of conditions in nursery habitats. In certain systems, spring or fall conditions were also important determinants of survival, suggesting additional effects of the environment on spawning of adults and juvenile egress from freshwater nursery habitats. [ABSTRACT FROM AUTHOR]

Dynamic programming is used to construct harvest control rules that account for persistent changes in productivity, exploitation rate constraints that prevent extinction of nontarget weak stocks, and an economic objective that recognizes moderate income to be more important to fishermen than maximization of total profit. Persistent productivity changes imply downward adjustment in spawning abundance targets during periods of low productivity, while conservation constraints simply imply upper limits on exploitation rate at high stock sizes. When the economic objective is to maximize the logarithm of net income (diminishing marginal utility or welfare from higher incomes), the optimum control rule shifts from a fixed escapement form to a curve where exploitation rate increases smoothly from zero at the minimum stock size that can be fished profitably to the upper limit set by a conservation constraint. This policy is not the fixed-exploitation rate form that has been historically suggested as a way of stabilizing harvests without major loss in profits. Application of harvest control rules constructed using dynamic programming in a mixed-stock salmon fishery in fact results in total profits close to those obtainable with fixed escapement policies but without the frequent low catches or closures implied by fixed escapement policies. [ABSTRACT FROM AUTHOR]

Intrafragment ecology is little studied for imperiled riverine fishes although river fragmentation and habitat loss increasingly threaten sensitive species. A long-term population-monitoring program in the Pecos River, New Mexico, provided detailed data for 15 annual cohorts of speckled chub ( Macrhybopsis aestivalis), which were used to assess intrafragment patterns in recruitment and year-class strength in relation to distributional patterns, flow-regime characteristics, and air temperature. Cohorts avoided a degraded upstream reach. Age-1 and older individuals had distributions consistently centered within a central, relict-ecosystem reach that contained high-quality habitat. Age-0 individuals were widespread within the relict-ecosystem reach and a channelized reach downstream. Distributional patterns suggested that some individuals that recruited in the channelized reach dispersed upstream into relict-ecosystem habitat thereafter. One cohort always numerically dominated the population because cohorts never lived beyond 2 years. Recruitment was density-independent and predicted year-class strength. No aspect of the flow regime explained variation in recruitment. Year-class strength was consistent among cohorts because of density-dependent mortality. High-quality habitat in a centralized location, potential for dispersal between channelized and relict-ecosystem reaches, and diffuse distribution of pelagic-broadcast propagules throughout both reaches combined to facilitate successful annual recruitment and population persistence. [ABSTRACT FROM AUTHOR]

We observed habitat occupancy by juvenile Chinook salmon ( Oncorhynchus tschawytscha) and steelhead trout ( Oncorhynchus mykiss) at in-stream habitat restoration structures constructed in the Entiat River, Washington, USA. In 2009-2013, fish abundance measurements during rearing (July-October) showed high temporal variability in pools with restoration structures. Both species were more abundant at restored pools than at natural pools in early summer (July), but this difference was typically absent by September. Fish response to restoration structures also varied across years. When looking only at restored pools, there were strong seasonal fluxes in parameters describing the effects of temperature, water depth, and current velocity on fish abundance. Significant interaction terms such as current velocity × depth and temperature × current velocity were present for both species, suggesting that these may be important physical attributes improved by restoration. Through extensive sampling in untreated habitat, both within the treated segment and in nearby control segments, we found that when higher Chinook abundance was observed at restored pools, it was apparently attributable to an increase in habitat capacity and not due to depletion of fish from natural habitat in the same segment. Steelhead habitat selection was too inconsistent for conclusions about capacity, but we did not observe evidence that structures depleted untreated habitat. [ABSTRACT FROM AUTHOR]

We used mark-recapture data from shovelnose sturgeon ( Scaphirhynchus platorynchus) to describe range-wide growth characteristics and developed a model to estimate ages. Data were solicited throughout much of the current distribution of shovelnose sturgeon, specifically from the mainstem Missouri and Mississippi rivers and their tributaries. Shovelnose sturgeon exhibited variable growth among locations; however, adult fish exhibited almost no growth after they reached a particular size, presumably the size at sexual maturity. Shovelnose sturgeon from the Mississippi River basin attained greater maximum sizes and ages compared with the Missouri River basin. However, two populations from the Mississippi River that received high exploitation from commercial harvest had truncated age distributions with smaller asymptotic lengths. Lower Missouri River populations were characteristic of exploited populations (i.e., smaller fish and reduced longevity), presumably a result of anthropogenic effects. Wide discrepancies in maximum age and size suggest shovelnose sturgeon are capable of displaying phenotypic plasticity in response to exploitation or environmental influences. Determining metapopulation dynamics is a priority because it is unknown how population connectivity may influence dynamic rate functions and persistence of large-river fishes. Identifying potential source-sink connections in terms of population dynamics may provide a template for direction of future restoration and recovery efforts. [ABSTRACT FROM AUTHOR]

Changes in resource development and expansions of urban centres suggest that the intensity and types of anthropogenic stressors affecting Canada's watersheds are changing. Chu et al. (2003) integrated indices of freshwater fish biodiversity, environmental conditions, and anthropogenic stress to identify priority watersheds for conservation and management. Here, we update those indices using recent climate and census data to assess changes through time. We also applied different conservation and management scenarios to evaluate the robustness of our prioritization approach. Between time periods, the environmental and stress indices expanded northward because of warmer temperatures at higher latitudes and more intense anthropogenic stress in the northern regions of the provinces. Conservation priorities increased in northern British Columbia, Alberta, and Ontario but decreased in southern British Columbia, Saskatchewan, and south-central Quebec. Under multiple scenarios, conservation priorities were consistently highest in British Columbia, the Maritimes, southern Ontario, and southern Quebec. Future research to refine this assessment should focus on developing a nationwide georeferenced assessment of freshwater fisheries stress, quantifying spatial changes in the stressors, and evaluating the sensitivity of each index to the weighting of the individual variables. This work highlights the necessity for conservation and management strategies in Canada to keep pace with changing patterns in climate and human activities. [ABSTRACT FROM AUTHOR]

Biological diversity is known to play an important role in generating and maintaining ecosystem productivity and other functions and has consequently become a central focus of many efforts to preserve ecosystem services. Theoretical parallels suggest the diversity of fishing fleets may have a similarly important role in determining the productivity and ecological impacts of fisheries, but this possibility has rarely been explored. Here I present theoretical analyses showing that the diversity of métiers - combinations of technology, target species, and fishing grounds - and technical efficiencies in a fishing fleet have important impacts on the productivity, profitability, and ecological impacts of fisheries, particularly mixed-stock or multispecies fisheries. Diversification of métiers can increase yields and reduce threats to weak stocks in both managed and unmanaged multispecies fisheries. Diversification of technical efficiencies creates opportunities for larger profits in managed fisheries, but often decreases yields and worsens impacts on weak stocks in unmanaged fisheries. These results suggest that the potential impact of management may be highest in fisheries with diverse fleets. [ABSTRACT FROM AUTHOR]

Biased perspectives of fisheries researchers may hinder scientific progress and effective management if limiting factors controlling productivity go unrecognized. We investigated whether river and lake researchers used different approaches when studying salmonid production and whether any differences were ecologically supported. We assessed 564 peer-reviewed papers published between 1966 and 2012 that studied salmonid production or surrogate variables (e.g., abundance, growth, biomass, population) and classified them into five major predictor variable categories: physical habitat, fertility (i.e., nutrients, bottom-up), biotic, temperature, and pollution. The review demonstrated that river researchers primarily analyzed physical habitat (65% of studies) and lake researchers primarily analyzed fertility (45%) and biotic (51%) variables. Nevertheless, understudied variables were often statistically significant predictors of production for lake and river systems and, combined with other evidence, suggests that unjustified a priori assumptions may dictate the choice of independent variables studied. Broader consideration of potential limiting factors on fish production, greater research effort on understudied genera, and increased publication in broadly scoped journals would likely promote integration between lentic and lotic perspectives and improve fisheries management. [ABSTRACT FROM AUTHOR]

Rapid increases in native riverine fish populations associated with trophic upsurge immediately following reservoir construction are well documented. Repeated upsurge periods and extended benefits to populations are, however, less understood. We used sclerochronology to investigate fish growth and netting surveys to estimate recruitment and abundance of a lacustrine population of an Australian riverine fish, the Macquarie perch ( Macquaria australasica) in Lake Dartmouth. Record low inflows from 1997 to 2008 caused the reservoir to shrink to its lowest volume since construction. Refilling began in 2008, reaching 99% capacity in 2013. We hypothesized that fish growth, recruitment, and abundance would increase in response to the refilling of the lake, reproducing a similar response to the initial filling period. Our findings supported this hypothesis. Macquarie perch growth, recruitment, and abundance were enhanced during the refilling of Lake Dartmouth. Growth, best explained by the effects of dam height, change in dam height, temperature (and their interactions), and recruitment, were highest during the first years of refilling when lake levels and temperatures were low. We propose one or a combination of varying levels of intraspecific competition (low during initial filling and high following population expansion) and improved riverine conditions for reproductive success as the most plausible explanation. Our results suggest extended periods of low lake levels followed by rapid inundation events are likely to enhance recruitment and population growth opportunities for this species. While reservoir construction in general impacts negatively on native fish populations, the potential to offset these impacts for conservation management purposes should be considered. [ABSTRACT FROM AUTHOR]

Assessment of population structure is critical to the design and implementation of sound management and conservation strategies. However, population structure must be assessed using markers attuned to population genetic processes such as genetic drift and gene flow, which reflect actual levels of reproductive isolation among putative genetic clusters. This is critical for highly exploited, commercial species that form the backbone of regional and local economies. Here, we show extremely low levels of population genetic differentiation among Greenland halibut ( Reinhardtius hippoglossoides) collected from throughout the Northwest Atlantic, which cannot be statistically differentiated from panmixia using 12 species-specific polymorphic microsatellite markers. In contrast, some previous studies have demonstrated significant differences among individuals collected from various parts of the species' range using a variety of both genetic and nongenetic techniques. In accordance with other reports and consistent with the species' life history, we demonstrate that the most parsimonious explanation reconciling observed patterns is a repeated high degree of local differentiation of new recruits and colonizers originating from a common gene pool. Such a scenario has important conservation implications in terms of devising more appropriate strategies balancing species persistence and replenishment with sustainable resource use. [ABSTRACT FROM AUTHOR]

How sea lampreys ( Petromyzon marinus) search for and select reproductive habitat is poorly understood. Manual tracking of acoustically tagged migrants confirms the hypothesis that sea lampreys transition from extensive search to intensive search upon encounter with river water and return to extensive search upon leaving the plume. In addition, we document a previously unknown search tactic used to localize river mouths termed coastal rebounding. Increased intensive search in the river plume and subsequent approach to the river mouth is hypothesized to occur as a consequence of detection of a pheromone released by river resident larvae that indicate the presence of high-quality reproductive habitat. Application of two synthesized pheromone components caused migrants to increase time spent searching a plume by 57%; applications did not increase the likelihood of river entry. These findings suggest that partial pheromones constitute information that facilitates the search for river entrances, but prove insufficient to affect the decision to select a habitat. Proposed management tactics that rely on luring migrants into rivers with larval odor may prove ineffective without a complete blend of pheromone components. [ABSTRACT FROM AUTHOR]