We used published information to determine optimum light and temperature conditions for walleye Sander vitreus (formerly Stizostedion vitreum) and then applied this simple niche definition to predict how water clarity, temperature, and bathymetry affect walleye habitat availability. Our model calculated thermal–optical habitat area (TOHA), the benthic area of a lake that supplies optimum light, and temperature conditions for walleye during an annual cycle. When water clarity is very low, little walleye habitat exists. As water clarity increases, TOHA for walleye initially increases and then declines exponentially. Optimum water clarity increases with maximum depth of the lake or, in the case of thermally stratified lakes, with thermocline depth. We tested this model by evaluating its ability to account for differences in the sustained yields of walleye fisheries on Ontario lakes. Our results demonstrate that (1) walleye harvest increases in proportion to TOHA times the square root of total dissolved solids, an index of nutrient level, and (2) optimum water clarity for walleye typically exists when Secchi depth is on the order of 2 m. These findings indicate that the increases in water clarity recently observed in the Great Lakes basin (as a result of phosphorus control and dreissenid mussel invasion) have reduced the supply of thermal–optical walleye habitat and, consequently have probably had negative effects on walleye production.

Freshwater aquatic organisms in North America are disproportionately imperilled when compared to their terrestrial counterparts due to widespread habitat alteration, pollution, overexploitation and the introduction of alien species. In this review, we examine the threat factors contributing to the endangerment of freshwater fishes and molluscs in Canada and further examine the nature of alien invasive species introductions affecting aquatic species at risk. Habitat loss and degradation is the predominant threat factor for Canadian freshwater fishes and molluscs that are listed as Extinct, Extirpated, Endangered and Threatened. Alien invasive species are the second most prevalent threat for fishes, affecting 26 of 41 listed species. Alien invasive species are a threat in most parts of Canada where listed fishes are found. Most (65%) of the alien invasive species affecting listed fishes are the result of intentional introductions related to sport fishing, and the majority of these introductions are unauthorized. Fifteen fishes and two plant species are cited as alien invasive species that impact listed fishes with brown bullhead (Ameiurus nebulosus) and pumpkinseed (Lepomis gibbosus) being the most prevalent. Alien species are a threat to 6 of 11 listed mollusc species. All six species are threatened by the alien zebra mussel (Dreissena polymorpha) in the Great Lakes basin.

The round goby (Neogobius melanostomus) first invaded North America in 1990 when it was discovered in the St. Clair River. Despite more than 15 years of potential invasion, many Great Lakes' lotic systems remained uninvaded. Recently, we captured the round goby from several Great Lakes tributaries known as species-at-risk hotspots. With a combination of field sampling of round gobies and literature review of the impact of round gobies on native taxa, we assess the potential impacts of the secondary invasion to native species using three mechanisms: competition; predation; and indirect impacts from the loss of obligate mussel hosts. We estimate that 89% (17/19) of benthic fishes and 17% (6/36) of mussels that occur in these systems are either known or suspected to be impacted by the secondary invasion of round goby. In particular, we note that the distribution of potential impacts of round goby invasion was largely associated with species with a conservation designation, including seven endangered species (1 fish, 6 mussels). As these recent captures of round goby represent novel occurrences in high diversity watersheds, understanding the potential impacts of secondary invasion to native biota is fundamental to prevent species declines and to allow early mitigation.

Summary Predictive models of species distribution are useful tools to identify habitats of imperilled species for protection, inventory and restoration. Critical aspects of such models include the influence of scale, uncertainties associated with imperfect detection and spatial autocorrelation and transferability of model predictions. We addressed these issues in developing occupancy models of the imperilled eastern sand darter (Ammocrypta pellucida) based on surveys of the Grand and Thames Rivers, Ontario, Canada. Eastern sand darter detection probabilities were remarkably different between streams, but factors affecting site occupancy were similar. The proportion of sand and fine gravel was most important, but water clarity and biotic indices also received support in additive models. Accounting for spatial autocorrelation reduced the effect of important covariates. Occupancy was more closely related to substratum at the site level than factors at broader scales (reach and valley segment), further emphasising the substratum specificity of this species. Almost all of the top‐ranked site and reach occupancy models had good predictive performance based on assessments of transferability. These models indicate that three formerly occupied Ontario catchments have a high probability of supporting the species and deserve consideration for repatriation. Our methods demonstrate how a comprehensive approach to occupancy modelling can be used to help guide recovery efforts for imperilled species.

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There are ~250,000 lakes in Ontario that support important cultural, recreational, and economic fisheries. In 2005, the Ontario Ministry of Natural Resources and Forestry adopted the Ecological Framework for Recreational Fisheries Management to tackle the heterogeneity of lake resources and angler mobility across the landscape, increase public participation in fisheries management, and streamline an ever‐growing list of regulations. The Broad‐Scale Monitoring Program for Inland Lakes began in 2008 to meet these goals. Essential elements of the program are: clear objectives, standardized sampling methods, operational implementation, diagnostic indicators, standardized reporting, a multidisciplinary team, and adaptive monitoring. Fishes, zooplankton, habitat, and angling activity are measured at each lake and provide the data needed to make evidence‐based fisheries management decisions. The data have benefited other provincial initiatives and provided significant contributions to the science of freshwater ecology. Recommendations are provided for other jurisdictions considering the implementation of a standardized broad‐scale monitoring program.

Captive breeding programs are widely applied by conservation practitioners as a means of conserving, reintroducing, and supplementing populations of imperilled freshwater fishes and mussels. We conducted a systematic map to provide an overview of the existing literature base on the effectiveness of captive breeding and release programs. A key finding is that there is limited evaluation of the effectiveness of such programs at all three stages (i.e., broodstock collection, rearing/release methods, and post-release monitoring). We identified clusters of evidence for supplementation evaluations related to rearing/release methods for fish growth and survival metrics, and the monitoring stage for fish genetic diversity, growth, and survival metrics, primarily focused on salmonids. However, many studies had inadequate experimental designs (i.e., lacked a comparator). Overall, there was a paucity of studies on the effectiveness of captive breeding programs for imperilled freshwater mussels, highlighting the need to make such information broadly available when studies are undertaken. Outputs from this systematic map (i.e., the map database and heatmaps) suggest that the effectiveness of captive breeding and release programs requires further systematic evaluation.

Fishes are among the most threatened taxa in Canada with over 70 species, subspecies, and (or) designatable units presently listed for protection under the Species at Risk Act (SARA). Protecting these species requires a diverse set of strategies based on the best-available data and information. One approach identified under SARA and in Canadian federal recovery strategies for improving the status of SARA-listed fishes is species reintroduction, which involves the release of individuals into areas from which they have been extirpated with the goal of re-establishing self-sustaining populations. The success of reintroduction relies on a comprehensive understanding of species ecology and life history, with considerations around population genetics and genomics. However, SARA-listed species are some of the most poorly known species in Canada due to their rarity and relative lack of research investment prior to the enactment of SARA. As a result, SARA-listed species have the most to lose if reintroduction activities are not carefully researched, planned, and executed. Therefore, the purpose of this review is to present an accessible summary on the state of reintroduction science for SARA-listed fishes in Canada with the hope of motivating future research to support reintroduction activities. We focus our review on 14 SARA-listed freshwater or anadromous fishes identified as candidates for reintroduction in federal recovery strategies. We follow the species-specific summaries with guidance on how basic research questions in population ecology, habitat science, and threat science provide a critical foundation for addressing knowledge gaps in reintroduction science. Subsequently, we identify the importance of genetic and genomic techniques for informing future research on the reintroduction of SARA-listed species. We conclude with recommendations for active, experimental approaches for moving reintroduction efforts forward to recover Canadian fishes.