Lake Chub Research Articles

The Finding and Description of A Diverse Population of the Southern Cestode Isoglaridacris agminis Williams and Rogers, 1972 (Caryophyllaidae) from Lake Chub Sucker Erimyzon sucetta (Lacépède, 1802) in a Northern Land-Locked Lake in Wisconsin, with a Special Reference to its Disjunct Post-Glacial Distribution in North America

Specimens of Isoglaridacris agminis Williams and Rogers, 1972 (Caryophyllidae) were first described from the lake chubsucker Erimyzon sucetta (Lacépède, 1802) in a small tributary of the Tallapoosa River at NE central Alabama. We have collected and examined I. agminis from the same host species in the land-locked Silver Lake, SE Wisconsin. We update our first and only 1986 account of this Wisconsin population, with new observations and measurements, and compare with those in the original and other descriptions. The morphology of I. agminis is revisited using light microscopy revealing new features. Emphasis is placed on the morphological variability of its unusual scolex and reproductive structures with variable ovarian shapes throughout development using many microscopic images. Measurements of 17 specimens and the re-examination of 15 more specimens from Silver Lake provided an opportunity to review the taxonomy and description of the species, distinguish locality differences, and correct and update other statements and concepts by other observers. The disconnected distribution of worms from the same host species in separate waters of various states is attributed to the disjunct post-glacial distribution of their primary hosts.

Incorporating Industrial and Climatic Covariates into Analyses of Fish Health Indicators Measured in a Stream in Canada’s Oil Sands Region

Industrial and other human activities in Canada’s oil sands region (OSR) influence the environment. However, these impacts can be challenging to separate from natural stresses in flowing waters by comparing upstream reference sites to downstream exposure locations. For example, health indicators of lake chub (Couesius plumbeus) compared between locations in the Ells River (Upper and Lower) in 2013 to 2015 and 2018 demonstrated statistical differences. To further examine the potential sources of variation in fish, we also analyzed data at sites over time. When fish captured in 2018 were compared to pooled reference years (2013–2015), results indicated multiple differences in fish, but most of the differences disappeared when environmental covariates were included in the Elastic Net (EN) regularized regression models. However, when industrial covariates were included separately in the EN, the large differences in 2018 also disappeared, also suggesting the potential influence of these covariables on the health of fish. Further ENs incorporating both environmental and industrial covariates along with other variables which may describe industrial and natural influences, such as spring or summer precipitation and summer wind speeds and distance-based penalty factors, also support some of the suspected and potential mechanisms of impact. Further exploratory analyses simulating changes from zero and the mean (industrial) activity levels using the regression equations respectively suggest effects exceeding established critical effect sizes (CES) for fish measurements may already be present or effects may occur with small future changes in some industrial activities. Additional simulations also suggest that changing regional hydrological and thermal regimes in the future may also cause changes in fish measurements exceeding the CESs. The results of this study suggest the wide applicability of the approach for monitoring the health of fish in the OSR and beyond. The results also suggest follow-up work required to further evaluate the veracity of the suggested relationships identified in this analysis.

Diets and Stable Isotope Signatures of Native and Nonnative Leucisid Fishes Advances Our Understanding of the Yellowstone Lake Food Web

(1) Many forage fishes, such as Leucisids (minnows) have depauperate studies on diet composition or stable isotope signatures, as these fishes are often only viewed as food for higher trophic levels. The need exists to understand and document the diet and stable isotope signatures of Leucisids (redside shiner, longnose dace, lake chub) in relation to the community ecology and food-web dynamics in Yellowstone Lake, especially given an invasive piscivore introduction and potential future effects of climate change on the Yellowstone Lake ecosystem. (2) Diet data collected during summer of 2020 were analyzed by species using proportion by number, frequency of occurrence, and mean proportion by weight, and diet overlap was compared using Schoener’s index (D). Stable isotope (δ15N and δ13C) values were estimated by collecting tissue during the summer of 2020 by species, and isotopic overlap was compared using 40% Bayesian ellipses. (3) Nonnative redside shiners and lake chub had similar diets, and native longnose dace diet differed from the nonnative Leucisids. Diet overlap was also higher between the nonnative Leucisids, and insignificant when comparing native and nonnative Leucisids. No evidence existed to suggest a difference in δ15N signatures among the species. Longnose dace had a mean δ13C signature of −15.65, indicating an decreased reliance on pelagic prey compared to nonnative Leucisids. Nonnative redside shiners and lake chub shared 95% of isotopic niche space, but stable isotope overlap was <25% for comparisons between native longnose dace and the nonnative Leucisids. (4) This study established the diet composition and stable isotope signatures of Leusicids residing in Yellowstone Lake, thus expanding our knowledge of Leucisid feeding patterns and ecology in relation to the native and nonnative species in the ecosystem. We also expand upon our knowledge of Leucisids in North America. Additionally, quantifying minnow diets can provide a baseline for understanding food web response to invasive suppression management actions.

Landscape, colonization, and life history: their effects on genetic diversity in four sympatric species inhabiting a dendritic system

To what degree are patterns of genetic structure in fragmented systems the result of contemporary landscape versus history? We examined the distribution of genetic diversity as a function of colonization history and contemporary landscape in four fish species inhabiting a hierarchically fragmented, unaltered system, the Kogaluk drainage (Labrador): lake trout (Salvelinus namaycush), longnose sucker (Catostomus catostomus), round whitefish (Prosopium cylindraceum), and lake chub (Couesius plumbeus). The footprint of colonization history was still observable in the three species where this issue was examined regardless of the generations since their arrival. Approximate Bayesian computation (ABC) analyses suggest colonization took place from the southwest. The species exhibit similar diversity patterns despite different [Formula: see text] values and generation intervals. Contemporary gene flow was largely negligible except for gene flow from a centrally located lake. These results suggest landscape has driven colonization history, which still has influence on genetic structuring. The species are widespread. Understanding how they behave in the pristine Kogaluk provides a baseline against which to evaluate how other anthropogenically perturbed systems are performing. Improved understanding of historical and contemporary processes is required to fully explain diversity patterns in complex metapopulations.

Forage fish and polycyclic aromatic compounds in the Fort McMurray oil sands area: Body burden comparisons with environmental distributions and consumption guidelines

The Fort McMurray region in northeastern Alberta (Canada) is rich in natural sources of polycyclic aromatic compounds (PACs) from exposed bitumen beds; anthropogenic sources are being released with increased oil sands industry expansion. Here we report on investigations of PACs (47 compounds) in three species of forage fish collected during the 2012–2013 Joint Oil Sands Monitoring Program (JOSMP) fish health investigations and compare results with PAC data for sediment and water collected under JOSMP and earlier programs. PAC concentrations in sediments varied three orders in magnitude and were highest at downstream tributary mouths, which flowed through the exposed McMurray Formation, and along reaches of the Athabasca River where the formation was exposed. PAC concentrations in water were less variable but with higher concentrations near exposed bitumen beds. Forage fish exhibited the weakest spatial gradients in ΣPACs concentration, which averaged 102 ± 32 ng/g in trout-perch from the Athabasca River, 125 ± 22 ng/g in lake chub from the Ells River, and 278 ± 267 ng/g in slimy sculpin from the Steepbank, Firebag, and Dunkirk Rivers. Low-molecular weight compounds, particularly naphthalenes and fluorenes, dominated fish PACs. Phenanthrenes occurred in greater percent composition in fish caught in areas where PAC concentrations in sediments were higher due to the proximity of bitumen sources than in other areas. Dibenzothiophene, a major component of bitumen PAC, was a minor component of fish ΣPACs. Forage fish PAC concentrations were below fish consumption guidelines established by the European Commission (2011) and for the reopening of the commercial fisheries closed by the Deepwater Horizon oil spill. PAC concentrations in forage fish were similar to concentrations observed in many other studies (fish market surveys, estuaries, and marine waters) and lower than in fish sampled from highly impacted areas (near refineries, harbors, and other industrialized areas).

Genetic structure and the history of chub in the Alvord Basin

Knowledge of the distribution of genetic resources within and among taxa is prerequisite for development of management strategies which facilitate conservation of those resources. We used restriction-site associated DNA (RAD) sequencing to survey genetic variation in Alvord Chub and Borax Lake Chub from the Alvord Basin in southeastern Oregon and northern Nevada, USA. Our specific goals were to gain an understanding of the population genetic structure of Alvord Chub and the relationship between this species and Borax Lake Chub. Despite the fact that our collections were taken from ponds and streams, isolated from one another by kilometers of desert, our results revealed that diversity in Alvord Chub was primarily distributed among two regional groupings, which we hypothesize to be related to habitat changes following the end of the most recent glaciation event, approximately 10 thousand years ago. Our results further revealed that Alvord Chub and Borax Lake Chub shared common ancestors during that glaciation event, and that divergence between the two may have been sympatric. Finally, we observed evidence that the clade containing Alvord Chub and Borax Lake Chub was isolated from its closest extant relative, the Tui chub, during the Miocene Epoch, when volcanic flows were forming the mountains surrounding what became the Alvord Basin. These results will be useful for informing conservation strategies for Alvord Chub, and provide new insights regarding the role of these species in the evolutionary legacy of the region.

Characterizing the Juvenile Fish Community in Turbid Alaskan Rivers to Assess Potential Interactions with Hydrokinetic Devices

AbstractInstallation of hydrokinetic power‐generating devices is currently being considered for the Yukon and Tanana rivers, two large and glacially turbid rivers in Alaska. We sampled downstream‐migrating fish along the margins of both rivers, a middle island in the Yukon River, and mid‐channel in the Tanana River in order to assess the temporal and spatial patterns of movement by resident and anadromous fishes and hence the potential for fish interactions with hydrokinetic devices. Results suggest that (1) river margins in the Yukon and Tanana rivers are primarily utilized by resident freshwater species, (2) the mid‐channel is utilized by Pacific salmon Oncorhynchus spp. smolts, and (3) only Chum Salmon O. keta smolts utilize both river margin and mid‐channel areas. Some species exhibited distinct peaks and trends in downstream migration timing, including Longnose Suckers Catostomus catostomus, whitefishes (Coregoninae), Arctic Grayling Thymallus arcticus, Lake Chub Couesius plumbeus, Chinook Salmon O. tshawytscha, Coho Salmon O. kisutch, and Chum Salmon. Due to their downstream migration behavior, Pacific salmon smolts out‐migrating in May–July will have the greatest potential for interactions with hydrokinetic devices installed in mid‐channel surface waters of the Yukon and Tanana rivers.

An Evaluation of the Efficiency of Minnow Traps for Estimating the Abundance of Minnows in Desert Spring Systems

AbstractDesert springs are sensitive aquatic ecosystems that pose unique challenges to natural resource managers and researchers. Among the most important of these is the need to accurately quantify population parameters for resident fish, particularly when the species are of special conservation concern. We evaluated the efficiency of baited minnow traps for estimating the abundance of two at‐risk species, Foskett Speckled Dace Rhinichthys osculus ssp. and Borax Lake Chub Gila boraxobius, in desert spring systems in southeastern Oregon. We evaluated alternative sample designs using simulation and found that capture–recapture designs with four capture occasions would maximize the accuracy of estimates and minimize fish handling. We implemented the design and estimated capture and recapture probabilities using the Huggins closed‐capture estimator. Trap capture probabilities averaged 23% and 26% for Foskett Speckled Dace and Borax Lake Chub, respectively, but differed substantially among sample locations, through time, and nonlinearly with fish body size. Recapture probabilities for Foskett Speckled Dace were, on average, 1.6 times greater than (first) capture probabilities, suggesting “trap‐happy” behavior. Comparison of population estimates from the Huggins model with the commonly used Lincoln–Petersen estimator indicated that the latter underestimated Foskett Speckled Dace and Borax Lake Chub population size by 48% and by 20%, respectively. These biases were due to variability in capture and recapture probabilities. Simulation of fish monitoring that included the range of capture and recapture probabilities observed indicated that variability in capture and recapture probabilities in time negatively affected the ability to detect annual decreases by up to 20% in fish population size. Failure to account for variability in capture and recapture probabilities can lead to poor quality data and study inferences. Therefore, we recommend that fishery researchers and managers employ sample designs and estimators that can account for this variability.Received September 29, 2014; accepted January 29, 2015

Development and characterization of 36 novel microsatellite markers for lake chub (Couesius plumbeus) using illumina paired-end sequencing

Lake chub is a common freshwater cyprinid found throughout Canada and parts of the northern United States. Here we describe 36 novel microsatellite loci, 25 of which are polymorphic, exhibiting between 2 and 17 alleles each, while the remaining 11 loci are monomorphic. Observed and expected heterozygosities for the polymorphic markers ranged from 0.125 to 0.875 and 0.146 to 0.878, respectively. There was no evidence of linkage disequilibrium between any locus pairs, nor was there any evidence of null alleles. There were however, six markers deviating from Hardy–Weinberg Equilibrium, a result we attribute to relatively small sample size.

Diel activity patterns of the fish community in a temperate stream

The diel activity patterns of fishes in a temperate New Brunswick stream were studied during the summer over 5 years. Young-of-the year Atlantic salmon Salmo salar and blacknose dace Rhinichthys atratulus were more active during the day than at night, whereas lake chub Couesius plumbeus, brook trout Salvelinus fontinalis and adult white suckers Catostomus commersonii were more active at night than during the day. Because fishes were as likely to be nocturnal as diurnal, the data suggest that more night-time sampling is needed to provide an unbiased view of fish community structure in temperate streams.

Setting Conservation Priorities in a Widespread Species: Phylogeographic and Physiological Variation in the Lake Chub, Couesius plumbeus (Pisces: Cyprinidae)

Defining units of conservation below the species level is a widely accepted conservation priority, but is especially challenging for widespread taxa that have experienced diverse geographic histories and exist across heterogenous environments. The lake chub (Pisces: Couesius plumbeus) is a widespread freshwater fish in North America and occurs from the southcentral USA to northwestern Alaska and Canada. We used mtDNA sequence analysis to test for divergent lineages predicted to occur as a result of survival of lake chub in distinct glacial refugia. Lake chub consisted of two major mtDNA lineages separated by 3.8% sequence divergence which are probably late to pre-Pleistocene in origin. We combined these data with those consistent with thermal adaptation in fish living in thermal springs versus those living in a lake with wide seasonal temperature variation, and with data on distribution of lake chub in major watershed units. We assessed these data against objective criteria developed to identify conservation units under Canadian endangered species legislation. Our analysis identified twelve major units of conservation within C. plumbeus that could be assessed under Canada’s Species-at-Risk Act. Our study illustrates how different character traits manifested at very different spatial scales can be used to define conservation units within widely-distributed taxa.

Assessing the food web impacts of an anadromousArctic charr introduction to a sub‐Arctic watershed using stable isotopes

AbstractAnadromousArctic charr,Salvelinus alpinus(L.), was introduced to a sub‐Arctic river–lake system near the village ofKujjuuaq,Nunavik, and the stable isotope values and diets of key resident fish species were used to assess changes in feeding patterns. Stable isotope values for most species did not differ significantly between the pre‐ and post‐introduction periods, with observed shifts being within the bounds of expected natural variation. Lake chub,Couesius plumbeus(Agassiz), were the single species to show a difference between study periods, with a small but significant increase in δ15N. No significant post‐introduction changes were seen in lake trout,Salvelinus namaycush(Walbaum), omnivory or in any of the assessed quantitative food web metrics. Gut contents of major fish species similarly showed significant temporal overlap between the pre‐ and post‐introduction periods, and there was no significant change in species' weight–length relationships. The minor ecological impact was interpreted in relation to the availability of open niches exploitable by ecological generalists such asArctic charr. The explanation accords with the known habitat and feeding flexibility ofArctic charr and the ecological immaturity of sub‐Arctic lakes known to have driven adaptive variation amongArctic charr. Findings suggest that anadromousArctic charr may be introduced at moderate densities to other sub‐Arctic watersheds without major negative food web consequences for other resident fish species.

Thermal Physiology of Warm-Spring Colonists: Variation among Lake Chub (Cyprinidae:Couesius plumbeus) Populations

In northern Canada, lake chub (Cyprinidae: Couesius plumbeus) have colonized a variety of thermal springs that differ substantially from the ancestral environment in both mean temperature and thermal variation. To examine whether this environmental change is associated with differences in physiological traits, we compared the thermal breadth, capacity for acclimation of thermal tolerance, and metabolic enzymes in populations of lake chub from three habitats: a warm but variable hot spring, a thermally constant warm spring, and a seasonally variable temperate lake. Thermal breadth was generally lowest in fish from the constant environment, and this difference was statistically significant in fish acclimated at 10° and 25°C. Critical thermal maximum (CT(max)) increased with increasing acclimation temperature in all populations. CT(max) was similar among populations when acclimated at high temperatures but greater in the variable-spring population acclimated to low temperature (10°C). Critical thermal minimum was also dependent on acclimation temperature in all populations but differed among populations such that fish from the stable-spring habitat were not as tolerant to cold temperature when acclimated to 25°C. Temperate- and variable-spring populations showed an increase in mitochondrial enzyme activities (citrate synthase and cytochrome c oxidase) with decreasing acclimation temperature, but this response was absent in the stable-temperature population. Protein content did not change with acclimation temperature in the stable-temperature population, while it increased with decreasing acclimation temperature in both variable thermal habitat populations. Our study suggests that interpopulation variation in thermal physiology is associated with habitat thermal variability.

Evaluating the trophic transfer of selenium in aquatic ecosystems using caged fish, X-ray absorption spectroscopy and stable isotope analysis

This research evaluated the dominant exposure pathways with regard to the bioaccumulation and trophic transfer of selenium (Se) in caged small-bodied fish inhabiting the receiving waters of a uranium-processing mill in northern Saskatchewan, Canada. A 21-day cage study was conducted using wild naïve lake chub ( Couesius plumbeus) collected from a reference lake and caged in a reference and an exposure lake downstream of the mill discharge. Caged fish were fed commercially produced Chironomus spp. diets of 1.5 (basal – commercial food) and 5.5 (lab reared in Se-spiked water) μg Se/g (dry weight) at a feeding ration of 10 percent percent body weight/day. Lake chub fed the Se-spiked diet and caged in the reference lake showed increased whole-body Se concentrations compared to chub fed the basal diet after 21 days. Lake chub caged in the exposure lake from both the elevated Se and basal diet groups had significantly greater whole-body Se concentrations compared to the reference lake, and were not significantly different from each other. The use of stable carbon (C), nitrogen (N), and sulphur (S) isotope analyses indicated that alternate benthic food sources native to the exposure lake were likely consumed in conjunction with the controlled diets. Stable isotope analysis of both wild and caged lake chub indicated that the N and S isotopic signatures decreased with increasing Se exposure, which was reflective of the differences in isotopic signatures of the food sources. Dose-dependent substitution of Se for S in methionine as a consequence of dietary Se exposure was illustrated by a decreasing whole-body S isotope signature and an increasing proportion of selenomethionine-like compounds (as measured by synchrotron-based X-ray absorption spectroscopy) with increasing Se exposure. Speciation results from caged lake chub indicated that Se substituted for S in methionine was the dominant Se species found in caged lake chub exposed to dietary sources of Se.

Selenium uptake and speciation in wild and caged fish downstream of a metal mining and milling discharge

The aim of this research was to evaluate the dominance of the feeding pathway with respect to selenium (Se) uptake and speciation in fish inhabiting the receiving waters downstream of a uranium processing mill in northern Saskatchewan, Canada. The experimental design included analysis of Se in the predominant fish species located in the study area, a caging validation study using wild, naïve (i.e., collected from a reference lake) lake chub ( Couesius plumbeus) and spottail shiner ( Notropis hudsonius), and a 21-day feeding cage study using wild naïve lake chub. Three exposure lakes located downstream of the uranium mill and one reference lake situated in an adjacent watershed were studied to investigate a gradient of Se exposure. Lake chub were identified as more suitable candidates for caging due to higher survival and condition factor at the completion of the 21-day trial. Analytical results indicated that lake chub caged in the exposure lakes had significantly greater whole-body Se concentrations after 21 days compared to fish caged in the reference lake. Selenium speciation results (obtained using X-ray absorption spectroscopy) from wild and caged lake chub indicated that organic Se modeled as selenomethionine was the dominant form of Se found in both wild and caged lake chub from the exposure lakes, and that selenomethionine (R–Se–R) acts as a marker of bioavailable Se exposure.

Wolf in sheep's clothing: Effects of predation by small-bodied fish on survival and behaviour of salamander larvae

Fish can affect amphibian larvae directly through consumption or indirectly by eliciting antipredator behaviours that incur fitness costs. Because of predation, long-toed salamanders (Ambystoma macrodactylum) typically show an allotopic distribution with fish. Linnet Lake (Waterton Lakes National Park, Alberta, Canada) represents the unusual situation in which salamanders coexist with a small-bodied cyprinid, lake chub (Couesius plumbeus). However, the salamander population resident to Linnet Lake has declined in recent years. Our objective was to assess the role of lake chub in the decline of this salamander population by combining field observations and laboratory experiments. We used mark-recapture techniques to estimate the size of the 2 populations. We found little evidence of successful salamander reproduction, and the adult population had decreased by 60% in 14 y. In contrast, a large population of lake chub was present. Experiments showed that lake chub between 70 and 100 mm could consume salamander larvae < 40 mm in length. Larvae responded to the presence of lake chub by reducing activity and increasing refuge use, especially during the day. Our study is one of few to document the ability of a native small-bodied fish to consume amphibian larvae. The coexistence of fish and salamanders may result from a dynamic interplay between periodic extirpation of fish by winter hypoxia and of salamanders by predation, punctuated by episodes of re-colonization or strong recruitment.

Occurrence of Lake Chub, &lt;em&gt;Couesius plumbeus&lt;/em&gt;, in Northern Labrador

Lake Chub (Couesius plumbeus) were recently found in seven previously undocumented locations in northern Labrador. These populations represent the first recorded accounts of this species in the Labrador region north of the Churchill River drainage and east of the George River. Lake Chub likely invaded this region via dispersal routes provided by eastern spillways of glacial Lake Naskaupi.

Cumulative Industrial Activity Alters Lotic Fish Assemblages in Two Boreal Forest Watersheds of Alberta, Canada

We evaluated the cumulative effects of land use disturbance resulting from forest harvesting, and exploration and extraction of oil and gas resources on the occurrence and structure of stream fish assemblages in the Kakwa and Simonette watersheds in Alberta, Canada. Logistic regression models showed that the occurrence of numerically dominant species in both watersheds was related to two metrics defining industrial activity (i.e., percent disturbance and road density), in addition to stream wetted width, elevation, reach slope, and percent fines. Occurrences of bull trout, slimy sculpin, and white sucker were negatively related to percent disturbance and that of Arctic grayling, and mountain whitefish were positively related to percent disturbance and road density. Assessments of individual sites showed that 76% of the 74 and 46 test sites in the Kakwa and Simonette watersheds were possibly impaired or impaired. Impaired sites in the Kakwa Watershed supported lower densities of bull trout, mountain whitefish, and rainbow trout, but higher densities of Arctic grayling compared to appropriate reference sites. Impaired sites in the Simonette Watershed supported lower densities of bull trout, but higher densities of lake chub compared to reference sites. Our data suggest that current levels of land use disturbance alters the occurrence and structure of stream fish assemblages.

Nearshore Habitat and Fish Community Associations of Coaster Brook Trout in Isle Royale, Lake Superior

AbstractWe characterized the nearshore habitat and fish community composition of approximately 300 km of shoreline within and adjacent to the major embayments of Isle Royale, Lake Superior. Sampling yielded 17 species, of which 12 were widespread and represented a common element of the Lake Superior fish community, including cisco Coregonus artedi, lake whitefish C. clupeaformis, round whitefish Prosopium cylindraceum, lake trout Salvelinus namaycush, rainbow smelt Osmerus mordax, lake chub Couesius plumbeus, longnose sucker Catostomus catostomus, white sucker C. commersonii, trout‐perch Percopsis omiscomaycus, ninespine stickleback Pungitius pungitius, burbot Lota lota, and slimy sculpin Cottus cognatus. The presence of brook trout S. fontinalis in an embayment was associated with the common species of the Isle Royale nearshore fish community, particularly cisco, longnose sucker, and round whitefish. However, brook trout were present in only five embayments and were common only in Tobin Harbor. Most Isle Royale embayments had broadly overlapping ranges of nearshore habitats. Within embayments, fish were distributed along a habitat gradient from less‐protected rocky habitat near the mouth to highly protected habitat with mixed and finer substrates at the head. Embayments with brook trout had greater mean protection from the open lake, greater variation in depth, greater mean cover, and higher mean frequencies of large substrates (cobble, boulder, and bedrock). Within those embayments, brook trout were associated with habitat patches with higher mean frequencies of small substrates (particularly sand and coarse gravel). Within Tobin Harbor, brook trout were associated with midembayment habitat and species assemblages, especially those locations with a mixture of sand, gravel, and cobble substrates, an absence of bedrock, and the presence of round whitefish, white sucker, and trout‐perch. Comparison of embayments with the model, Tobin Harbor, showed that six embayments without brook trout had very similar arrays of habitat. However, four embayments with brook trout had relatively different arrays of habitat from Tobin Harbor. These results suggest that there is potential for further recovery of brook trout populations across Isle Royale nearshore habitats.

Hearing in eight species of northern Canadian freshwater fishes

The hearing thresholds of eight fish species from northern Canada were measured using auditory evoked potential techniques. The species with the best hearing was the lake chub Couesius plumbeus, followed by the longnose sucker Catastomus catastomus, both which had relatively sensitive hearing over the frequency range tested from 100 to 1600 Hz. The remaining species (troutperch Percopsis omiscomaycus, nine‐spined stickleback Pungitius pungitius, pike Esox lucius, spoonhead sculpin Cottus ricei, burbot Lota lota and broad whitefish Coregonus nasus) all showed most sensitivity to low frequencies (&lt;400 Hz) and had relatively insensitive high frequency hearing. The two species with the best hearing are otophysan fishes with connections between the swimbladder and inner ear. The spoonhead sculpin lacks a swimbladder, while the other non‐otophysan species have swimbladders, but no specialized connection to the inner ear. These results can be used to predict the potential impact of anthropogenic noise, such as seismic air gun blasts, on hearing in these species. The species with the most sensitive hearing (lake chub and longnose sucker) are most likely to be affected by activities such as seismic air gun surveys.