In situ and laboratory feeding trials coupled with stomach content analysis of largemouth bass (Micropterus salmoides) were performed to examine how turbidity influences the size selectivity and capture rates of prey. No significant differences in the capture success of adult largemouth bass preying on northern redbelly dace (Phoxinus eos) were observed during in situ feeding trials in two Lake Ontario coastal wetlands differing in turbidity level (2.3 and 20 nephlometric turbity units (NTU)). During 1-h laboratory feeding trials, the overall number of fathead minnows (Pimephales promelas) captured was not significantly different among 1-, 18-, and 37-NTU treatments. However, at 70 NTU, the number of fathead minnows captured was significantly lower than that at the lowest turbidity treatment. Selection by juvenile largemouth bass of the smallest size-class of fathead minnow decreased as turbidity increased. No significant differences in piscivory were apparent between juvenile largemouth bass collected from turbid and clear habitats. Stomach content comparisons of juvenile largemouth bass seined from six clear and turbid habitats suggest that piscivory is primarily regulated by the availability of vulnerable size-classes of prey fish, as opposed to water clarity.

The study of cisco diversity in inland lakes of North America has been plagued by taxonomic uncertainty linked to high phenotypic plasticity and an ongoing reliance on morphology to differentiate species. More recently, this uncertainty has hindered the development of conservation plans and status assessments of ciscoes. This study presents the first range-wide comparison of morphological and genetic variation between Cisco (Coregonus artedi) and Shortjaw Cisco (C. zenithicus). Using morphological and genetic data from 17 lakes, three sets of analyses were undertaken to evaluate alternate hypotheses explaining the pattern of cisco phenotypic diversity in inland lakes. Morphotypes (MTs) representing the two taxa were phenotypically distinct (largely reflective of differences in gill raker number and jaw morphology) within lakes but highly variable across lakes. Shortjaw Cisco was only recognizable when compared to sympatric Cisco and some populations were morphologically similar to Cisco from other lakes. Analysis of AFLP data revealed two genetic clusters that conformed to differences in geography (eastern and western groups), rather than hypothesized taxonomic boundaries. Genetic variation strongly suggests that each of these unique sympatric pairs of MTs originated recently and locally, in parallel, from the ancestral Cisco. Phenotypic and genetic distinctiveness between MTs were not related. MTs were sometimes clearly recognizable despite a lack of genetic differentiation, suggesting that the canalization of phenotypic plasticity is unevenly completed across lakes. These results provide evidence that the taxonbased approach is clearly inadequate for the protection of Shortjaw Cisco. In Canada, status assessment should aim to identify lake-specific designatable units (DU). Given the idiosyncratic nature of each instance of Shortjaw Cisco, it is expected that the strength of morphological, biological, ecological and genetic evidence for individual DUs will vary among lakes.

Data from Lake Ontario tributaries were used to evaluate the efficacy of single-pass backpack electric fishing for stream fish monitoring by: testing the relationship between single-pass catch-per-unit-effort (CPUE) and multiple-pass-based population estimates; comparing species richness estimates derived from single-pass and multiple-pass data and assessing the concordance of fish assemblage patterns described using single-pass and multiple-pass data. Significant correlations were calculated between single-pass CPUE and removal-based population estimates for total catch, 15 species, six taxonomic families, five feeding and four reproductive guilds and tolerant/intolerant species. Strong correlations were more commonly associated with the abundance of individual species than other metrics. Capture probability was not affected by stream size or habitat complexity for most measures. Species accumulation curves and significant correlations (r 2 = 0.9) between single-pass and multiplepass electric fishing indicate that single-pass surveys provide a representative index of species diversity. In addition, within and among-site variation in fish community composition based on single-pass and multiple-pass data were similar.K E Y W O R D S : assessment, backpack electric fishing, fish community, sampling, stream.

Dams have the potential to affect population size and connectivity, reduce genetic diversity, and increase genetic differences among isolated riverine fish populations. Previous research has reported adverse effects on the distribution and demographics of black redhorse (Moxostoma duquesnei), a threatened fish species in Canada. However, effects on genetic diversity and population structure are unknown. We used microsatellite DNA markers to assess the number of genetic populations in the Grand River (Ontario) and to test whether dams have resulted in a loss of genetic diversity and increased genetic differentiation among populations. Three hundred and seventy-seven individuals from eight Grand River sites were genotyped at eight microsatellite loci. Measures of genetic diversity were moderately high and not significantly different among populations; strong evidence of recent population bottlenecks was not detected. Pairwise F ST and exact tests identified weak (global F ST = 0.011) but statistically significant population structure, although little population structuring was detected using either genetic distances or an individual-based clustering method. Neither geographic distance nor the number of intervening dams were correlated with pairwise differences among populations. Tests for regional equilibrium indicate that Grand River populations were either in equilibrium between gene flow and genetic drift or that gene flow is more influential than drift. While studies on other species have identified strong dam-related effects on genetic diversity and population structure, this study suggests that barrier permeability, river fragment length and the ecological characteristics of affected species can counterbalance dam-related effects.

Redhorse, Moxostoma spp., are considered to be negatively affected by dams although this assertion is untested for Canadian populations. One hundred and fifty-one sites in the Grand River watershed were sampled to identify factors influencing the distribution of redhorse species. Individual species of redhorse were captured from 3 to 32% of sites. The most widespread species were golden redhorse, M. erythrurum (30%) and greater redhorse, M. valenciennesi (32%), while river redhorse, M. carinatum, was only found along the lower Grand River. Redhorse were absent from the highly fragmented Speed River subwatershed and upper reaches of the Conestogo River and the Grand River. Redhorse species richness was positively correlated to river fragment size and upstream drainage area. Generalized additive models (GAMs) were applied to evaluate the influence of river fragment length, connectivity and habitat on species distribution. Principal component analysis reduced habitat data to three axes representing: channel structure, substrate, and pool, riffle and run habitats (PC1); gradient and drainage area (PC2); and cover (PC3). GAMs indicate that PC2 was important for predicting black redhorse and greater redhorse site occupancy and PC1 was important for golden redhorse. River fragment length was important for predicting site occupancy for shorthead redhorse, but not other species.

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To date, monitoring of the status of the provincially threatened redside dace Clinostomus elongatus in Ontario has been ad hoc or incidental to other sampling programs. We evaluated the efficacy of single-pass backpack electrofishing without block nets to detect redside dace, provide an index of abundance, and characterize size-class distributions. We also examined whether a rapid stream habitat assessment method was suitable for monitoring habitat condition at redside dace sites. Based on 40 sites across 7 Lake Ontario tributaries, catch data and length frequency distributions from single-pass sampling were compared with those from multiple-pass depletion sampling. Single-pass electrofishing captured 47% of estimated redside dace abundance and 34% of biomass. Abundance and biomass data from the single-pass method were positively correlated (abundance r 2 ¼ 0.83; biomass r 2 ¼ 0.52) with estimates from the multiple-pass depletion method. Probability of detection and precision of single-pass estimates of abundance were similar to those reported in previous studies on stream salmonids. Single-pass and multiple-pass length frequency distributions were not significantly different. The habitat assessment method failed to detect expected habitat differences between sites that contained redside dace and those that did not. Habitat monitoring could be improved by including more detailed measurements of fine sediment, pool depth, and riparian vegetation.