R. Allen Curry

Examination of the responses of slimy sculpin (Cottus cognatus) and white sucker (Catostomus commersoni) collected on the Saint John River (Canada) downstream of pulp mill, paper mill, and sewage discharges.

As part of a larger survey on cumulative effects within the Saint John River basin (Canada), a fish survey was conducted near Edmundston (NB, Canada) in the fall of 1999 using slimy sculpin (Cottus cognatus) and white sucker (Catostomus commersoni). The discharge environment receives effluent from the pulp mill, a paper mill, three sewage discharges, and tributaries receiving agricultural runoff. Sculpin collected downstream of the sewage discharges and pulp mill effluent had greater growth, condition, and liver size but no significant differences in gonad size. Stable isotope data indicated slimy sculpin did not move between sites. Female sculpin collected downstream of the paper mill showed no significant differences in length, body weight, age, condition factor, liver size, and gonad size compared to fish from reference sites. Female white sucker collected downstream of the pulp mill did not differ significantly in any measured parameter compared to reference fish. Liver sizes of white sucker from the Saint John River were outside the range considered to be indicative of uncontaminated riverine sites. In 2000, sculpin collected downstream from a poultry-processing facility had larger livers and lower condition factors, suggesting that the site is contaminated. We found no significant differences in sculpin length, weight, condition (except for males), and liver size in sculpin collected downstream from the pulp mill in October 2001. The responses of slimy sculpin and white sucker differed, perhaps in relation to differences in life history characteristics. Results from this study indicate the slimy sculpin is a suitable fish species for monitoring rivers that receive multiple industrial and municipal effluents.

Spatial and Temporal Movements of a Riverine Brook Trout Population

Abstract The year-round movements of brook trout Salvelinus fontinalis were monitored in a large river (125 km) and brackish-water estuary by using radio and acoustic tags and a fish counting fence over a 3-year period. Trout moved upstream 65-100 km during the spring after ice loss over a protracted 4-month period (April-July). Summer movements were minimal, and habitats were deep pools and runs with cover in the same reaches each year. Trout moved short distances (<10 km) to spawning areas in the fall (September). Downstream movements were observed for both postspawned and immature trout. By the time of the river freeze-up (January), major movements had ceased and trout wintered in the lower to middle reaches of the main river, with only one trout leaving the river. That fish remained in habitats with salinity less than 5‰ during winter and returned to the river by May. By improving the scale of observation, we identified an apparent mix of tactics related to the use of marine and freshwater environment...

High fidelity: isotopic relationship between stream invertebrates and their gut contents

Abstract Benthic macroinvertebrate families were sampled along 3 rivers in New Brunswick, Canada. Stable isotopes of C and N were compared between body tissue and gut contents of individuals. δ13C and δ15N of body tissue and gut contents were strongly correlated (r = 0.94 and 0.93, respectively) over a wide range of δ values. In nonpredators, only minor fractionation of δ13C and δ15N was observed. In predators, diet–tissue fractionation of 13C was minor, but 15N fractionation that may have been related to diet quality (N content) was observed. The influence of diet quality on N-isotope fractionation was inconsistent in direction and strength among families. Our results suggest that subjecting primary consumers to gut clearance prior to processing for stable-isotope analysis is unnecessary, but the guts of predators should be removed before processing.

Population-level responses to sediment during early life inbrook trout

Abstract The spawning sites, incubation success, and density of young-of-the-year (YOY) brook trout (Salvelinus fontinalis) were examined in stream populations experiencing varying levels of sediment stress. Our objective was to determine effects on embryos and YOY and examine cumulative effects on the populations. Early development was unaffected (88% survival). Mortality occurred at late, encapsulated embryo stages likely as a function of oxygen deprivation within redds. Survival to emergence from the substrate was significantly reduced (∼50%) in redds in which fine sediments accumulated. Groundwater reduced sediment accumulation in redds and enhanced survival. Sediment may have affected dispersal of YOY trout. All populations appeared successful in term of total density (average = 72/100 m2). Our findings emphasize the importance of targeting multiple life-history stages and understanding local adaptations when searching for true population-level effects in any stressed ecosystem.

Increasing Mercury in Yellow Perch at a Hotspot in Atlantic Canada, Kejimkujik National Park

In the mid-1990s, yellow perch (Perca flavescens) and common loons (Gavia immer) from Kejimkujik National Park and National Historic Site (KNPNHS), Nova Scotia, Canada, had among the highest mercury (Hg) concentrations across North America. In 2006 and 2007, we re-examined 16 lakes to determine whether there have been changes in Hg in the loon’s preferred prey, yellow perch. Total Hg concentrations were measured in up to nine perch in each of three size classes (5−10 cm, 10−15 cm, and 15−20 cm) consumed by loons. Between 1996/97 and 2006/07, polynomial regressions indicated that Hg in yellow perch increased an average of 29% in ten lakes, decreased an average of 21% in three, and were unchanged in the remaining three lakes. In 2006/07, perch in 75% of the study lakes had Hg concentrations (standardized to 12-cm fish length) equal to or above the concentration (0.21 μg·g−1 ww) associated with a 50% reduction in maximum productivity of loons, compared with only 56% of these lakes in 1996/97. Mercury contamination currently poses a greater threat to loon health than a decade ago, and further reductions in anthropogenic emissions should be considered to reduce its impacts on ecosystem health.

Genetic Population Structure of Brook Trout Inhabiting a Large River Watershed

Abstract The genetic population structure of brook trout Salvelinus fontinalis inhabiting the Miramichi River, New Brunswick, a large (14,000-km2) river system composed of three main stems, was assessed using six microsatellite DNA loci. Samples from 12 sites incorporating four temporal replicates were analyzed. An individual-based assignment method without a priori knowledge of geographic origin suggested the presence of five candidate source populations within the 12 sites. Drainage structuring based on the 12 sampling sites did not explain the observed patterns of genetic population structure (analysis of molecular variance: 0.74% of variance explained; not significant). Conversely, the five candidate source populations estimated under the assignment approach significantly explained the genetic population structure observed (3.47% of variance explained; P < 0.001), the level of population fragmentation within sampling sites increasing significantly with proximity to the mouth of the watershed (P = 0.01...

Linking landscape variables to cold water refugia in rivers

The protection of coldwater refugia within aquatic systems requires the identification of thermal habitats in rivers. These refugia provide critical thermal habitats for brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) during periods of thermal stress, for example during summer high temperature events. This study aims to model these refugia using georeferenced thermal infrared images collected during late July 2008 and 2009 for a reach of the Cains River, New Brunswick, Canada. These images were paired with geospatial catchment variables to identify the driving factors for coldwater refugia located within tributaries to the main channel. Using Partial Least Square (PLS) Regression, results suggest that median temperatures of tributary catchments are driven by their position within the landscape including slope in addition to the density of wetlands and mixed forest within the upstream catchment. Similar results are presented when PLS models were developed to predict the magnitude of the cold water refugia (i.e. the difference between the mainstem water temperature and the thermal refugia). These results suggest that thermal infrared images can be used to predict critical summer habitats for coldwater fishes.

Impacts of nonpoint inputs from potato farming on populations of slimy sculpin (Cottus cognatus)

The potential influence of agricultural activity, particularly potato cultivation, on slimy sculpin populations (Cottus cognatus) was examined at 19 rivers of New Brunswick, Canada. Comparisons with forested streams resulted in differences in fish density, size, and reproductive performance. Young-of-the-year (YOY) sculpin were present only at two of 11 agricultural sites, though they were present at all nine forested sites. Sediment deposition was greatest at agricultural sites, with increased fine sediments deposited. Larger, coarse sands were deposited at two sites with active forest operations. Temperature had a stronger correlation than sedimentation with sculpin size and density in the agricultural region. Agricultural catchments were warmer than in forested catchments (median = 16.0 and 13.3 degrees C, respectively). Body size of slimy sculpin was correlated positively and YOY densities correlated negatively with temperature, and sites with temperatures > or = 25 degrees C were devoid of YOY sculpin. Our data indicate there is a significant effect of temperature on slimy sculpin populations in rivers of potato farming areas, highlighting the importance of examining indirect factors when investigating possible impacts of nonpoint source agricultural inputs. Indirect factors such as sediment deposition and temperature need to be considered in order to discriminate accurately the chronic impacts of agricultural chemicals on fish populations.

The origins and persistence of anadromy in brook charr

We synthesized the results of a coordinated study examining the spatial and temporal movements, genetic structure, and physiological characteristics of sympatric populations of resident and sea-run brook charr across eastern Canada. Our goal was to critically evaluate three working hypotheses that may explain anadromous behaviour in brook charr: (1) resident and anadromous forms have different phylogenic origins; (2) anadromy emerges from freshwater residents; and (3) freshwater residency emerges from anadromous individuals. Our synthesis is consistent with the conclusion that freshwater residency emerging from anadromous individuals is most probable. Overall, anadromy in brook charr is poorly developed and the tactic of sea-running may be described as partial, facultative anadromy if the species must be described in terms of anadromy. The sea-run tactic most probably results from the species’ propensity to move and disperse, the over-production of juveniles, an archetypical physiological ability to tolerate saline environments, and the persistence of critical habitats. When the spatial and temporal physical environments permit, the anadromous behaviour is expressed. The tactic creates an apparent fitness advantages related to growth, but it is not necessarily the only evolutionary stable strategy for a river. Most populations with sea-run forms are declining and successful conservation of sea-run forms will depend on managing harvests and more importantly, protection of the temporally and spatially complexity of critical habitats.

The rainbow smelt, Osmerus mordax, complex of Lake Utopia: threatened or misunderstood?

We report on the spawning ecology, genetic characteristics, and predation threats to spawning groups of rainbow smelt, Osmerus mordax, in Lake Utopia, New Brunswick where a dwarf morpho-type has been listed as a threatened species. Two spawning groups in three inlet streams had been previously identified; we observed three groups using four inlet streams. The earliest group was the largest in body size (12–29 cm fork length (FL)), lowest in numbers (∼1 000), and completed spawning approximately two weeks before the second group. The early spawners were previously identified as the normal morpho-type, but we now classify these as a giant morpho-type. The second group spawned in three different streams. They were intermediate in body size (10–15 cm FL) and numbers (∼10 000). The dwarf group began spawning as the intermediate group completed spawning and within the same three streams. The dwarfs were numerous (∼1 000 000), small in size (<12 cm), and with higher gill raker counts. Microsatellite analyses suggested that gene flow among groups occurred, but genetic divergence was high and genetic separation among populations of the same group among streams and within a stream occurred. Stable isotopes and stomach contents indicated the dwarf group were likely consumed by a variety of fishes, but they were not the sole food resource of any predator including a population of landlocked salmon. These are some of the complexities of smelt ecology, but there are clearly life history tactics that we do not yet understand.