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Quantifying the responses of rare and vulnerable species to environmental stressors poses special challenges. This study examined the responses of vulnerable fish species listed under the Species at Risk Act to environmental stressors in lakes, streams, and wetlands of the Canadian Great Lakes basin. We used a joint species distribution model (JSDM) to improve the estimates of responses of vulnerable species to environmental stressors, and the effects of functional traits on those responses, by "borrowing information" from abundant species for which we have more information. We measured abundance, functional traits, and taxonomic relationships for 115 freshwater fish species (including 12 vulnerable species), and environmental features, at 1972 sites. The JSDM yielded more precise estimates of responses than single-species models fitted to each vulnerable species. Habitat associations inferred from the JSDM showed substantial overlap with those provided in COSEWIC status reports. Model-derived responses to environmental stressors can provide a management-friendly basis for species classification in terms of species' tolerances to various forms of environmental change, and supplement the qualitative criteria for habitat requirements currently used in assessments of species vulnerability. [ABSTRACT FROM AUTHOR]

Hydromorphological descriptors such as substrate type, water depth, and velocity are commonly used to describe fish habitat, but few studies have focused on how underwater sounds affect habitat use by freshwater fish. We evaluated the influence of the underwater soundscape and other habitat descriptors on the spatial distribution of brook trout (Salvelinus fontinalis) in a small stream in eastern Canada. Habitat measurements were made at high spatial resolution (2.5 m intervals). High acoustical heterogeneity of stream habitats (40–150 dB re 1 μPa) was related to differences in water velocity and depth as expected from theory. Brook trout densities were positively related to broadband sound pressure levels (SPL), irrespective of water velocity and depth, but in interaction with habitat type. The positive relationship between brook trout densities and SPL could be related to the high auditory threshold of salmonid fishes. Alternatively, brook trout may use the underwater soundscape to select favourable feeding habitats. Underwater sounds integrate the many environmental dimensions of a stream and may be used by fish as cues for habitat selection. [ABSTRACT FROM AUTHOR]

Although lakes and rivers are intimately connected, more effort is needed to develop conceptual approaches accounting for lake-stream interactions within the drainage network. Lakes can buffer the impacts of environmental variability in streams and facilitate stream fish recolonization processes. However, lakes have rarely been incorporated in habitat models for stream fish. We examine whether including the presence of lakes in habitat models can improve our understanding of brook trout ( Salvelinus fontinalis) abundance in streams. We quantified brook trout relative abundance in 36 streams over 3 consecutive years by single-pass electrofishing. Relative abundance of brook trout in streams was greatest when lakes were present in the stream network. Lakes had greater influence on relative abundance in headwater streams than in larger streams. These results emphasize the importance of considering lakes as a critical attribute in landscape fish habitat models, many of which focus on terrestrial landscape variables. We discuss potential gains from incorporating the presence of lakes in ( i) multiscale habitat models, ( ii) analyses of spatiotemporal distribution of thermal refuges, and ( iii) metrics of habitat connectivity in lake-stream networks. [ABSTRACT FROM AUTHOR]

We quantified fish abundance and environmental variables at 170 sites distributed among 11 tributaries of the Ottawa River, Quebec, Canada, to assess the relative importance of among- and within-tributary variation in riverine fish assemblages. Additionally, we determined (i) which environmental variables were most strongly associated with each type of variation and (ii) whether ecomorphological traits in fish assemblages were predictably related to environmental gradients. Partitioning of variation by means of partial ordination indicated that assemblages were less variable among (38.7% of the total variation) than within (61.3%) tributaries. Water transparency singly accounted for 33.3% of the variation among tributaries, whereas macrophyte cover and river width jointly accounted for 8.3% of the variation within tributaries. These results suggests that differences in habitat features among tributaries may account for a substantial fraction of the predictable variation in assemblage structure at the watershed scale, an aspect not emphasized in previous studies of riverine fish assemblages. Mixed regression analyses relating ecomorphological traits to environmental variables showed that the environmental variables most strongly associated with assemblage structure were significantly related to traits associated with predator avoidance or foraging efficiency. [ABSTRACT FROM AUTHOR]

Shallow fluvial lakes are heterogeneous ecosystems in which marked spatio-temporal variation renders difficult the analysis of key ecological processes, such as growth. In this study, we used generalized additive modelling of the RNA/DNA ratio, an index of short-term growth, to investigate the influence of environmental variables and spatio-temporal variation on growth of yellow perch (Perca flavescens) in Lake St. Pierre, Quebec, Canada. Temperature and water level had seemingly stronger effects on short-term growth than seasonal change or spatial variation between and along the lakeshores. Consistent with previous studies, the maximum RNA/DNA ratio was found at 20.5 °C, suggesting that our approach provides a useful tool for estimating thermal optima for growth in the field. The RNA/DNA ratio showed a positive relationship with water level, as predicted by the flood pulse concept, a finding with implications for ecosystem productivity in fluvial lakes. The RNA/DNA ratio was more variable along the north than the south shore, possibly reflecting exposure to more differentiated water masses. The negative influence of both high temperatures and low water levels on growth points to potential impacts of climatic change on fish production in shallow fluvial lakes. [ABSTRACT FROM AUTHOR]

We used classification trees and regression trees to relate the incidence and density of juvenile Atlantic salmon (Salmo salar) to forestry activities measured at four spatial scales (subbasin and 8, 2, and 0.5 km radii upstream of study sites) and environmental features in 120 stream reaches of the Cascapedia River basin, Québec, Canada. At all scales, incidence increased with reach size and accessibility to the reach from the river mainstem. Incidence declined with areal coverage of logging at all scales, but only in larger reaches. The time horizon over which logging effects were detected increased with spatial scale. At all scales, density in salmon-bearing reaches increased with accessibility. Density in more accessible reaches was negatively related to logging over the preceding 9 years at the subbasin and 8 km scales, but no effects of logging on density were detected at the 2 and 0.5 km scales. Overall, apparent effects of logging activities on salmon incidence and density were mostly negative and strong, but were both markedly scale-dependent and conditional on environmental context. [ABSTRACT FROM AUTHOR]

We used hierarchical linear regression to examine relationships between brook trout (Salvelinus fontinalis) density and habitat features nested at three levels: sections within reaches, reaches within streams, and streams within a basin. Brook trout density and environmental variables were quantified at 600 stream sections distributed among 120 reaches and 22 streams in the Cascapedia River basin, Quebec, Canada. Decomposition of variance showed that variation in density among streams was small relative to that among sections or reaches and not statistically significant. Density was influenced by habitat variables at both the section (current velocity, woody debris, cover) and reach (subbasin area, height increment at flood, valley width) levels. A cross-level interaction between current velocity and subbasin area pointed to a "contextual" effect: density showed stronger decline with current velocity in larger subbasins than in smaller subbasins. This result suggests that there was no single "best scale" for examining fish–environment relationships. Accounting for contextual effects by use of hierarchical models can enhance our understanding of how habitat features influence fish densities at multiple spatial scales. [ABSTRACT FROM AUTHOR]

The objective of this study was to measure and model the response time of the Eastern Canadian Diatom Index (IDEC: Indice Diatomées de l'Est du Canada), a diatom-based index of biological integrity, following substrate translocation from altered sites (nutrient-enriched) to pristine sites and vice-versa. The frequency of sampling, duration (time after substrate translocation), and variety of site conditions in the present study provide strong evidence for an accelerated response of diatoms to a degradation reflecting eutrophication (within a week in certain cases) and a slower path to recovery (up to 4 weeks). Diatom response varied as a function of trophic status; oligotrophic rivers responded rapidly to a degradation, and mesotrophic or eutrophic rivers responded more slowly to an amelioration of the conditions. Variation in response time as a function of trophic status seemed to be partly linked to the diversity and complexity of the assemblages. The less diverse assemblages observed in oligotrophic waters were highly sensitive to nutrient enrichment, whereas the more diverse assemblages sampled in mesotrophic-eutrophic rivers were less sensitive to nutrient fluctuations, and major variations in nutrient concentrations took a longer time to induce a change in index values. L'objectif de notre recherche est de mesurer et de modéliser le temps de réaction de l'Indice Diatomées de l'Est du Canada (IDEC), un indice d'intégrité biologique basé sur les diatomées, à la suite d'un déplacement de substrats de sites altérés (enrichis en nutriments) vers des sites vierges et vice-versa. La fréquence de l'échantillonnage, la durée (temps écoulé depuis le déplacement des substrats) et la variété des conditions dans les sites de notre étude permettent d'obtenir des données probantes qui montrent une réaction accélérée des diatomées à une dégradation qui représente une eutrophisation (en moins d'une semaine, dans certains cas) et une voie de récupération plus lente (jusqu'à 4 semaines). La réaction des diatomées varie en fonction du statut trophique : les rivières oligotrophes réagissent rapidement à une dégradation, alors que les rivières mésotrophes ou eutrophes réagissent plus lentement à une amélioration des conditions. La variation du temps de réaction en fonction du statut trophique semble être reliée en partie à la diversité et la complexité des peuplements. Les peuplements moins diversifiés observés dans les eaux oligotrophes sont très sensibles à l'enrichissement par les nutriments, alors que les peuplements plus diversifiés échantillonnés dans les rivières mésotrophes-eutrophes sont moins sensibles aux fluctuations des nutriments; les variations majeurs dans les concentrations de nutriments mettent donc plus de temps à provoquer un changement dans les valeurs de l'indice. [ABSTRACT FROM AUTHOR]

Effective conservation requires that species recovery measures are informed by rigorous scientific research. For imperilled freshwater fishes and mussels in Canada, numerous research gaps exist, in part owing to the need for specialized research methods. The Canadian Freshwater Species at Risk Research Network (SARNET) was formed and identified or implemented approaches to address current research gaps, including (1) captive experimental research populations, (2) nonlethal methods for estimating abundance and distribution, (3) nonlethal field methods to measure life-history parameters, (4) species distribution models informed by co-occurring species, (5) conservation physiology to inform habitat and threat science, (6) evidence syntheses to evaluate threats and recovery measures, (7) disease-transmission models to understand mussel–host relationships, (8) experimental mesocosms and manipulative experiments to evaluate key habitat stressors, (9) threat and hazard models for predictive applications, and (10) rigorous evaluation of surrogate species. Over a dozen threat- and recovery-focused SARNET research applications are summarized, demonstrating the value of a coordinated research program between academics and government to advance scientific research on, and to support the recovery of, imperilled freshwater species. [ABSTRACT FROM AUTHOR]

Phenotypic variability represents an important factor allowing species to adapt to local environmental conditions, but mechanisms underlying such variation are incompletely understood. This study investigated whether habitat-specific demands on swimming performance or difference in trophic relationships in lakes (pelagic, littoral) and streams (riffle, pool) were significant predictors of phenotypic variation exhibited by brook char ( Salvelinus fontinalis), the only fish in the study habitats. Specifically, we hypothesized that pelagic and riffle habitats would impose greater selective pressures associated with swimming, resulting in body morphologies that were dorsoventrally compressed, anterior-posteriorly elongated, and that exhibited a long, narrow caudal peduncle. Geometric morphometrics was applied in a quantitative analysis of body morphology among habitats, whereas stable isotope analysis was used to differentiate between food sources. Analyses revealed that while body morphology differed between lake and stream habitats, there was convergence between the pelagic and riffle habitats, as well as among littoral and riffle and pool environments. The littoral and pool habitats were thought to be more structurally complex, thereby selecting for increased maneuverability but lower sustained swimming and correspondingly deeper bodies with shorter, dorsoventrally expanded caudal peduncles. Carbon source and trophic position did not differ among habitats with a system, suggesting that feeding was not the main influence on morphological plasticity; however, fish in the stream were feeding at a higher trophic position than fish in the lake. These findings suggest that individual species may take advantage of morphological variation to better adapt local surroundings. [ABSTRACT FROM AUTHOR]