Search

This study identifies the current spatial and temporal patterns of threats to at-risk freshwater fishes within Canada. Data for 65 at-risk freshwater fishes were collated from the Committee on the Status of Endangered Wildlife in Canada Assessment and Status reports with threat calculators. Using these data, the overall threat impact level and the threat impact of the 11 categories in the threat calculator were compared for all species and separately by conservation status, which indicates their risk of extinction. These threats were also compared temporally to a study completed in 2006 and spatially between National Freshwater Biogeographic Zones. The threats of invasive species and pollution had the highest impacts, accounting for 18.9% and 16.8% of the weighted impact on at-risk freshwater fishes, respectively. Since 2006, all threats have been increasing, except for natural disasters. The Great Lakes–Upper St. Lawrence River Biogeographic Zone had significantly more at-risk freshwater fishes and overall weighted threat impact than other zones, with pollution, invasive species, and natural system modification contributing the most to the imperilment in this region. [ABSTRACT FROM AUTHOR]

When dealing with invasive fishes, permanent barriers may inhibit spread, but may not be feasible due to costs and logistical constraints. Alternatively, non-permanent barriers using electricity, light, sound, pressure, bubbles, and CO2 are being developed and deployed in efforts to limit and prevent the spread of aquatic invasive species or to achieve fish guidance and conservation. However, the effectiveness of these barriers is quite variable and testing is often lacking for both invasive and native species. We conducted a laboratory experiment to investigate the impact of vertical electric barrier on behaviour of Rainbow Trout, Oncorhynchus mykiss. In response to electric current, Rainbow Trout responded by significantly decreasing passage through the electric barrier zone and spending more time away from the electric barrier when it was turned on during the stimulus period compared to pre-stimulus period. Moreover, when interacting with electric barrier, Rainbow Trout exhibited certain behaviours (e.g. stunned and remained on the same side of the barrier, stunned and crossed the barrier) more than others (e.g. approach and retreat, deflected, and paralyzed). Moreover, it appears that Rainbow Trout remained distant from the electric barrier even after the electric barrier was turned off. Our results indicate that relatively weak electric gradient (i.e. voltage gradient: 0.2 – 0.4 v·cm−1, power density: 3 – 42 µW·cm−3) can inhibit the movement of Rainbow Trout. Our results also highlight the importance of detailed investigation of behavioural responses of target species when evaluating and considering fish-deterrent or guidance technologies. [ABSTRACT FROM AUTHOR]

Biodiversity loss is a serious issue for freshwater fishes in temperate climates and there is a need for more information in this area. A study was conducted to assess fish community changes in the littoral zone of 22 lakes over a 45 year period (compared years 1969-1979 and year 2014). To compare fish communities, historical seining records were compiled for 22 inland lakes and compared with contemporary data sampled using the same protocol. Fish abundance data analyzed using a multivariate approach identified a shift from cyprinid-dominated communities to centrarchid-dominated communities between time periods. There was no evidence to support a strong influence of invasive species on these communities, but there have been significant changes in temperature and land use around these lakes since the historical data sets were collected. This is an important contribution to our understanding of biodiversity change in North American freshwater fish communities and may influence fisheries management approaches in the future. [ABSTRACT FROM AUTHOR]

When managing invasive fishes, permanent barriers may be best in preventing spread; however, they may not be feasible due to costs and logistical constraints. Alternatively, non-permanent barriers using electricity, light, sound, pressure, bubbles, CO2, and other stimuli are being developed and deployed in efforts to limit the spread of aquatic invasive species or to achieve fish guidance and conservation. However, the effectiveness of these barriers is quite variable and testing is often lacking for both target and non-target species. We conducted a series of laboratory trials to examine the effects of a vertical electric barrier on behaviour of common carp Cyprinus carpio (Linnaeus, 1758). In response to the electric field, common carp reduced passing the electric barrier significantly, exhibiting different behaviours when interacting with the electric barrier, and spent more time away from the electric barrier when it was turned on during the stimulus period compared to preand post-stimulus periods. Our results suggest that a relatively weak electric gradient (i.e., voltage gradient: 0.2-0.4 V·cm-1, power density: 3-42 μW·cm-3) can inhibit the movement of common carp. Our results also highlight the importance of detailed examination of behavioural responses of target species when evaluating and considering fish-deterrent technologies. [ABSTRACT FROM AUTHOR]

The secondary invasion of the round goby (Neogobius melanostomus) into tributaries of the Laurentian Great Lakes has resulted in ecological impacts on many native benthic species. However, the ecological impacts on white sucker (Catostomus commersonii), a native benthic species has not been examined. A comparative control and invaded site study design was used to examine diet overlap and the dietary impact of the round goby invasion on white sucker's trophic niche. We found significant diet overlap between round goby and white sucker, and white sucker in sympatry with round goby shift their feeding strategy to be more generalist when compared to white sucker in uninvaded locations. No influence of diet competition with round goby on the trophic niche of white sucker was found in this study. Our results support the hypothesis that white sucker are experiencing competition for prey items with round goby. These increased competitive interactions may exacerbate the observed declines in white sucker abundance as round goby continue their invasion upstream in Lake Ontario tributaries. [ABSTRACT FROM AUTHOR]

Non‐structural deterrents may limit invasive fish dispersal and range expansion without altering waterflow or navigation. Despite extensive research in laboratory and artificial environments, few studies have been conducted in situ and, of those, few have evaluated the full community response of fishes interacting with the deterrent. We deployed acoustic deterrents within a physical trap‐and‐sort fishway at Cootes Paradise, Ontario, Canada, to determine the avoidance responses of a community of fishes attempting to disperse into the wetland.To test the effectiveness of an acoustic deterrent, the catch rates of fishes entering Cootes Paradise were compared when the deterrent was off (control) and on (treatment). Community diversity was fit to candidate generalised linear models, and common carp catch abundance was fit to candidate generalised additive models, both of which were compared with backwards selection. The presence of a phylogenetic signal in fish responses was assessed with Pagel's λ and Blomberg's K indices of trait evolution.Over 11,500 fishes, representing 16 species and 12 families, were captured. The acoustic deterrent did not alter the Shannon diversity of fishes challenging the fishway, but a significant phylogenetic signal in species‐specific avoidance responses was observed. There was a modest decrease in the catch rates of common carp (ambient trials = 1.03 fish/hr, deterrent trials = 0.84 fish/hr), a species of major management concern.Fish avoidance responses to acoustic deterrents were widely variable, and species specific. The avoidance response of common carp, the target species, was weak, probably due to a complex acoustic environment surrounding the fishway. Group size did not alter deterrent efficacy, but precipitation, water temperature, and turbidity did.Our study successfully quantified acoustic deterrent responses across an entire community of wetland fishes, including both native and invasive species. We are the first to demonstrate that there is a phylogenetic component to deterrent responses across species. We also identify environmental parameters that alter deterrent efficacy in the field, and describe important considerations for the deployment of non‐structural deterrents in the field. [ABSTRACT FROM AUTHOR]

Despite the promising applications of genome-wide information to conservation, the field of conservation genomics remains hindered by a research-practice gap. Identifying the benefits from genomics in relation to fish conservation planning and decision-making could contribute to bridging this gap. The goals of our study were twofold. First, we reviewed the fish conservation genomic literature to determine how genomic information has been used to inform conservation decision making; and second, we examined how genomic information can be linked to an existing conservation decision framework. Our review showed that, as fish conservation genomics studies accumulate over time, collaborations between researchers and conservation practitioners are becoming increasingly frequent. While the field is dominated by studies of economically important families (e.g. salmonids, acipenserids) in first-world countries (North America, Europe), it has a broad taxonomic coverage where species of both local and global conservation concern are well represented. We also show that genomic information can readily be harnessed to guide decisions within existing conservation decision frameworks, from the conceptualization (identification of conservation targets and threats) to the implementation and the monitoring of conservation actions. In addition, our review identifies some limitations related to genomic inferences for conservation and proposes solutions to address these uncertainties and improve communication between conservation genomic scientists and practitioners. For genomic researchers, we outline how conservation decisions are made; for practitioners, we illustrate how genomic information can inform decision-making. [ABSTRACT FROM AUTHOR]

Detection of invasive species is critical for management but is often limited by challenges associated with capture, processing and identification of early life stages. DNA metabarcoding facilitates large‐scale monitoring projects to detect establishment early. Here, we test the use of DNA metabarcoding to monitor invasive species by sequencing over 5000 fishes in bulk ichthyoplankton samples (larvae and eggs) from four rivers of ecological and cultural importance in southern Canada. We were successful in detecting species known from each river and three invasive species in two of the four rivers. This includes the first detection of early life‐stage rudd in the Credit River. We evaluated whether sampling gear affected the detection of invasive species and estimates of species richness, and found that light traps outperform bongo nets in both cases. We also found that the primers used for the amplification of target sequences and the number of sequencing reads generated per sample affect the consistency of species detections. However, these factors have less impact on detections and species richness estimates than the number of samples collected and analysed. Our analyses also show that incomplete reference databases can result in incorrectly attributing DNA sequences to invasive species. Overall, we conclude that DNA metabarcoding is an efficient tool for monitoring the early establishment of invasive species by detecting evidence of reproduction but requires careful consideration of sampling design and the primers used to amplify, sequence and classify the diversity of native and potentially invasive species. [ABSTRACT FROM AUTHOR]

Predicting how quickly populations expand their range and whether they will retain genetic diversity when they are introduced to new regions or track environmental conditions suited to their survival is an important applied and theoretical challenge. The literature suggests that long‐distance dispersal, landscape heterogeneity and the evolution of dispersal influence populations' expansion rates and genetic diversity. We used individual‐based spatially explicit simulations to examine these relationships for Tench (Tinca tinca), an invasive fish expanding its geographical range in eastern North America since the 1990s. Simulated populations varied greatly in expansion rates (1.1–28.6 patches year−1) and genetic diversity metrics, including changes in observed heterozygosity (−19 to +0.8%) and effective number of alleles (−0.32 to −0.01). Populations with greater dispersal distances expanded faster than those with smaller dispersal distances but exhibited considerable variation in expansion rate among local populations, implying less predictable expansions. However, they tended to retain genetic diversity as they expanded, suggesting more predictable evolutionary trajectories. In contrast, populations with smaller dispersal distances spread predictably more slowly but exhibited more variability among local populations in genetic diversity losses. Consistent with empirical data, populations spreading in a longer, narrower dispersal corridor lost more neutral genetic variation to the stochastic fixation of alleles. Given the unprecedented pace of anthropogenic environmental change and the increasing need to manage range‐expanding populations, our results have conservation ramifications as they imply that the evolutionary trajectories of populations characterised by shorter dispersal distances spreading in narrower landscapes are more variable and, therefore, less predictable. [ABSTRACT FROM AUTHOR]

Biodiverse habitats are increasingly subject to an intensification of anthropogenic stressors that may severely diminish species richness. Invasive species pose a dominant threat to biodiversity and biosecurity, particularly in biodiversity hotspots like Kruger National Park, South Africa. The invasive silver carp, Hypophthalmichthys molitrix, was introduced into the Olifants River and may experience range spread owing to favorable environmental conditions. Intensive monitoring protocols are necessary to effectively manage invasions of species like silver carp. Unfortunately, tropical and sub-tropical aquatic systems are difficult to monitor using conventional methods (e.g., netting, electrofishing and snorkeling) owing to a range of factors including the presence of dangerous megafauna. Conservation of such systems may be advanced by the adoption of novel methods, including environmental DNA (eDNA) detection. Here, we explore the utility of environmental DNA (eDNA) to conduct safe, reliable and repeatable surveys in dangerous watersheds using silver carp as a case study. We conducted eDNA surveys at 12 sites in two neighbouring watersheds, and determined that the species has expanded its range within the Olifants River and to the south in the Sabie River. Expansion in the former is consistent with the presence of suitable spawning conditions. We discuss the implications of this survey for biodiversity monitoring in similar aquatic systems in the tropics and advocate an integrative approach to biomonitoring in these ecosystems. [ABSTRACT FROM AUTHOR]

Since the early Holocene, fish population genetics in the Laurentian Great Lakes have been shaped by the dual influences of habitat structure and post‐glacial dispersal. Riverscape genetics theory predicts that longitudinal habitat corridors and unidirectional downstream water‐flow drive the downstream accumulation of genetic diversity, whereas post‐glacial dispersal theory predicts that fish genetic diversity should decrease with increasing distance from glacial refugia. This study examines populations of seven native fish species codistributed above and below the 58 m high Niagara Falls – a hypothesized barrier to gene flow in aquatic species. A better understanding of Niagara Falls' role as a barrier to gene flow and dispersal is needed to identify drivers of Great Lakes genetic diversity and guide strategies to limit exotic species invasions. We used genome‐wide SNPs and coalescent models to test whether populations are: (a) genetically distinct, consistent with the Niagara Falls barrier hypothesis; (b) more genetically diverse upstream, consistent with post‐glacial expansion theory, or downstream, consistent with the riverscape habitat theory; and (c) have migrated either upstream or downstream past Niagara Falls. We found that genetic diversity is consistently greater below Niagara Falls and the falls are an effective barrier to migration, but two species have probably dispersed upstream past the falls after glacial retreat yet before opening of the Welland Canal. Models restricting migration to after opening of the Welland Canal were generally rejected. These results help explain how river habitat features affect aquatic species' genetic diversity and highlight the need to better understand post‐glacial dispersal pathways. [ABSTRACT FROM AUTHOR]

The Anthropocene Epoch is characterized by novel and increasingly complex dependencies between the environment and human civilization, with many challenges of biodiversity management emerging as wicked problems. Problems arising from the management of biological invasions can be either tame (with simple or obvious solutions) or wicked, where difficulty in appropriately defining the problem can make complete solutions impossible to find. We review four case studies that reflect the main goals in the management of biological invasions - prevention, eradication, and impact reduction - assessing the drivers and extent of wickedness in each. We find that a disconnect between the perception and reality of how wicked a problem is can profoundly influence the likelihood of successful management. For example, managing species introductions can be wicked, but shifting from species-focused to vector-focused risk management can greatly reduce the complexity, making it a tame problem. The scope and scale of the overall management goal will also dictate the wickedness of the problem and the achievability of management solutions (cf. eradication and ecosystem restoration). Finally, managing species that have both positive and negative impacts requires engagement with all stakeholders and scenario-based planning. Effective management of invasions requires either recognizing unavoidable wickedness, or circumventing it by seeking alternative management perspectives. [ABSTRACT FROM AUTHOR]