Garry J. Scrimgeour

Size-dependent diel foraging periodicity of a mayfly grazer in streams with and without fish

We tested the hypothesis that predation risk from diurnal fish influences the diel foraging periodicity of the mayfly grazer, Baetis tricaudatus Dodds, in a size-dependent manner by examining habitat use and foraging activity of mayflies in streams with and without these fish predators. In each stream diel habitat use was determined by counting the number of small (3 mm total length) and large (6 mm total length) Baetis larvae foraging on the upper surfaces of replicate, natural cobble during 4-8 sampling periods within a 24-h cycle over three seasons. Additionally, larvae were collected and preserved so that the dial periodicity in gut fullness could be determined

Foraging and evading predators: the effect of predator species on a behavioural trade-off by a lotic mayfly

We performed laboratory experiments to test the hypothesis that predator species influenced a foragers trade-off between predation risk and food reward. Larvae of the stream mayfly, Baetis tricaudatus Dodds, were provided with simultaneous access to feeding patches in laboratory streams that differed in predation risk (safe, risky) and food reward (low, high). Predation risk was imposed using either: (1) a fish predator, the longnose dace, Rhinichthys cataractae (Valenciennes), (2) a stonefly predator, Claassenia sabulosa (Banks), and (3) both predators is risky patches at the same time. We hypothesized that predator species would influence the behavioural trade-off between predation risk and food reward because mortality risk on Baetis from Rhinichthys exceeds that from Claassenia

Anti-Predator Responses of Mayfly Larvae to Conspecific and Predator Stimuli

Hydrodynamic and water-borne chemical stimuli are considered important cues that initiate anti-predator behaviours of mayfly larvae. We tested the hypotheses that chemical stimuli from conspecifics and the predacious fish Rhinichthys cataractae and hydrodynamic stimuli from a Rhinichthys model would initiate anti-predator responses by mayfly larvae of Ephemerella aurivillii, Paraleptophlebia heteronea, and Baetis tricaudatus. A second set of experiments tested the hypotheses that chemical stimuli from conspecifics and the predacious stonefly Claassenia sabulosa and hydrodynamic stimuli from a Claassenia model would initiate responses by Baetis. These hypotheses were tested in laboratory streams where mayfly larvae received either chemical stimuli, hydrodynamic stimuli, or the combination of hydrodynamic and chemical stimuli. Responses by larvae to these stimulus types, in terms of use of substratum surfaces and drift rates, were compared with those by larvae in control streams without conspecific and predator stimulus types. Responses to chemical stimuli were variable depending upon mayfly species and the chemical stimulus type. For instance, while Ephemerella and Paraleptophlebia responded to Rhinichthys odours, Baetis did not respond to either Rhinichthys or Claassenia odours. Paraleptophlebia responded to conspecific odours whereas Ephemerella and Baetis did not. In contrast, all three mayfly species responded to hydrodynamic stimuli either alone or when combined with chemical stimuli. Responses by Baetis were more complex when chemical stimuli were combined with hydrodynamic stimuli. For instance, although Baetis did not respond to conspecific odours alone, drift was significantly higher in streams receiving the three stimuli of conspecific odours, predator odours from Rhinichthys, and hydrodynamic stimuli from a Rhinichthys model when compared with streams that received only the conspecific odours combined with the fish model. Similarly, an enhanced response was observed when Baetis odours were combined with Claassenia odours and the Claassenia model. Thus, the lack of a response to a chemical stimulus did not preclude an enhanced response when combined with other stimulus types. These observations suggest that although some mayflies are capable of detecting the presence of some chemical stimuli, a response is not elicited unless the stimulus is accompanied by additional stimuli.

Nutrient enrichment of northern rivers in response to pulp mill and municipal discharges

To evaluate the effects of pulp mill and municipal sewageeffluents on the nitrogen (N) and phosphorus (P) status of northernCanadian rivers, the Northern River Basins Study required an integratedresearch and assessment program consisting of field observation andexperimentation. Analysis of monitoring data collected over 3–13 yshowed that on an annual basis, pulp mills contributed 22% of theP and 20% of the N load discharged from the Wapiti to the Smokyriver, and 6 to 16% of the P load and 4 to 10% of the Nload in the Athabasca River. Despite these low contributions, N and Pconcentrations were elevated below pulp mill discharges on all threerivers during the low discharge period of September to April. Insitu experiments conducted with nutrient diffusing substrata showedthat periphyton biomass was maintained at low levels by insufficient Pin the upper reaches of the Athabasca River and insufficient N+P inthe Wapiti River upstream of point-source discharges. In contrast,effluent loading from pulp mill and sewage inputs alleviated nutrientlimitation downstream of major discharges on both rivers. Experimentsconducted in artificial streams located beside the Athabasca Riverupstream of the first pulp mill showed that P addition increasedperiphyton biomass (expressed as chlorophyll a content) suchthat biomass increased sharply at low P concentrations (2–5µg/L soluble reactive P) and approached saturation at 35µg/L soluble reactive P. As a result of recommendations fromthis integrated program of river monitoring and experimentation,nutrient loading has been reduced to the most affected river(Wapiti-Smoky) and federal and provincial departments of environment arereviewing loading limits for other river reaches.

δ13C and δ15N Signatures in Muscle and Fin Tissues: Nonlethal Sampling Methods for Stable Isotope Analysis of Salmonids

Abstract Stable isotope analysis has emerged as an important tool in aquatic ecology. For fish, dorsal muscle from sacrificed individuals has traditionally been used in stable isotope studies; however, there are many instances when lethal sampling is undesirable. We evaluated the feasibility of using adipose and caudal fin clips as alternatives to muscle in stable isotope studies for five species of salmonids. Because fish size and water temperature can affect stable isotope ratios, we also determined whether fish length and sampling date affected the difference in isotope signatures between fins and muscle. Biopsied muscle plugs and fin clips were collected from rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, and lake trout S. namaycush as well as lake whitefish Coregonus clupeaformis and pygmy whitefish Prosopium coulterii and analyzed for stable isotopes of carbon and nitrogen. The isotope signatures of both adipose and caudal fins were significantly correlated (0.33 < R 2 < 0.97)...

Aquatic Ecosystem Health and Integrity: Problems and Potential Solutions

Stable URL:http://links.jstor.org/sici?sici=0887-3593%28199606%2915%3A2%3C254%3AAEHAIP%3E2.0.CO%3B2-6Journal of the North American Benthological Society is currently published by The North American Benthological Society.Your use of the JSTOR archive indicates your acceptance of JSTORs Terms and Conditions of Use, available athttp://www.jstor.org/about/terms.html. JSTORs Terms and Conditions of Use provides, in part, that unless you have obtainedprior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content inthe JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained athttp://www.jstor.org/journals/nabs.html.Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.JSTOR is an independent not-for-profit organization dedicated to and preserving a digital archive of scholarly journals. Formore information regarding JSTOR, please contact support@jstor.org.http://www.jstor.orgSat Jun 9 14:08:22 2007

Simulated fine woody debris accumulations in a stream increase rainbow trout fry abundance

Abstract Habitat for young-of-the-year rainbow trout Oncorhynchus mykiss was enhanced in a fourth-order stream during August–October 1991 by the addition of wooden structures that simulated accumulations of fine woody debris (FWD). The experiment represented a two-factorial design with the presence or absence of FWD bundles and time since debris introduction as factors. Immediately after FWD placement, fry density, individual biomass, fry condition factor, and total fry biomass were similar in treated and untreated sites. As the experiment progressed, density and total fry biomass significantly increased at treated but not at untreated sites. Individual biomass and condition factor did not differ between treated and untreated areas, and they were affected only by time since FWD placement. Because individuals at treated and untreated sites were the same size, added FWD did not affect an individuals net rate of energy gain. Rather, we hypothesize that the FWD provided structurally complex habitat that acte...

Transferability of Habitat Suitability Curves for a Benthic Minnow, Rhinichthys cataractae

Abstract Physical Habitat Simulation (PHABSIM) is used to predict the impact of flow regime alterations on habitat availability of fish. Species-specific predictions of habitat availability for fish are often made by applying generic habitat suitability curves (HSC), thereby implicitly assuming that HSCs are fixed among rivers. We tested the hypothesis that HSCs for a widely-distributed North American minnow, the longnose dace (Rhinichthys cataractae), were similar in two rivers in western Canada. Utilization curves differed between rivers for all three parameters, but the mechanism producing these differences was different. Although transferability tests provide an objective method of assessing whether an existing curve is applicable to a new river system, our findings indicated the tests often failed because the test statistic was not applicable to the raw data. R. cataractae populations displayed large variations in HSC for water depth, water velocity, and substratum composition between the study river...

Effects of Forest Harvesting and Fire on Fish Assemblagesin Boreal Plains Lakes: A Reference Condition Approach

Abstract To assess the impacts of forest harvesting and fires on lentic fish assemblages in the Boreal Plains ecoregion (Alberta, Canada), we applied a reference condition approach to 37 lakes in burned, logged, or undisturbed catchments. Fish assemblages in the reference lakes were classified into two types: those dominated by large-bodied piscivores and those dominated by small-bodied fishes. A discriminant function analysis with only two environmental descriptors (lake maximum depth and average slope of the catchment) could correctly predict assemblage type in 84% of reference lakes. Depth likely reflects the influence that winter oxygen concentrations have on fish assemblage type, whereas catchment slope is correlated with a variety of landscape-level features. Although potential effects of forest harvesting and fire can increase the susceptibility of lakes to winter hypoxia (via nutrient enrichment) and alter connectivity to the regional drainage network (via altered hydrology), fish assemblages in 9...

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.