Miller, M., Stevens, C. and M. S. Poesch. (In Press). Effectiveness of spawning substrate enhancement for adfluvial fish in a regulated sub-Arctic river. River Research and Applications.


This study was conducted to meet regulatory requirements under the Fisheries Act in Canada, specifically for a hydroelectric facility on the Yellowknife River in the Northwest Territories. The research focused on annual snorkel surveys of adfluvial fish and their spawning habitat below the facility. Initial observations of egg mortality, potentially due to overcrowding, prompted the investigation of natural and enhanced habitat for spawning Lake trout (Salvelinus namaycush), lake whitefish (Coregonus clupeaformis) and cisco (Coregonus artedi) from 2016 to 2019. The design and composition of the installed habitat were based on fish utilization of the natural channel below the hydro facility and design principles from previous habitat rehabilitation projects for anadromous fishes. Pre- and post-enhancement data on egg density and survival were collected using 1 m2 plots on both natural and artificially enhanced substrates. Three years of post-enhancement monitoring indicated higher egg densities and a greater proportion of live eggs in the artificially enhanced habitat compared to the natural habitat, with more pronounced trends observed for coregonids (lake whitefish and cisco) compared to lake trout. These findings suggest that habitat enhancement has the potential to enhance juvenile recruitment for adfluvial fish. A critical factor in the design was the substrate composition, providing adequate interstitial spaces for egg development and protection. This study represents the first documented attempt at habitat improvement in a regulated sub-Arctic river in Canada. The findings offer valuable guidance for stakeholders involved in new or existing development projects that require conservation actions to maintain fisheries productivity.

Citation: Miller, M., Stevens, C. and M. S. Poesch. (In Press). Effectiveness of spawning substrate enhancement for adfluvial fish in a regulated sub-Arctic river. River Research and Applications.

Also Read:

McPherson, M.*, Lewis, J.B., Cott, P.B., Baker, L.F., Mochnacz, N.J. Swanson, H.K., and S. Poesch. (2023) Habitat use by fluvial Arctic Grayling (Thymallus arcticus) across life stages in northern mountain streams. Environmental Biology of Fishes 106: 1001-1020.

*Lab members: Mark Poesch. Check out opportunities in the lab!

MacLeod, T. (2023) Assessing the station holding ability of three benthic fishes exposes to flow augmentation: implications for species at risk.

Thesis Title: Assessing the station holding ability of three benthic fishes exposes to flow augmentation: implications for species at risk.

Author: Taylor (Macs) MacLeod


Flow augmentation forces Plains Sucker in the Milk River to adopt more efficient station holding mechanisms, which must be energetically costly as they are not maintained year-round. The station holding ability of Milk River Plains Sucker was measured using a Brett-style swim tunnel respirometer, and the results were compared to other catostomid species in the Milk River and to Plains Sucker caught in water bodies that remain unmodified year-round. Milk River Plains Sucker maintained a significantly higher estimated marginal mean failure velocity (p < 0.0001) during augmentation (June-July) compared to natural flows (September-October). Catostomids in Milk River exhibited varying degrees of response; from no change in response to augmentation (Longnose Sucker, p = 0.5) to a significant shift (Plains Sucker and White Sucker p =
0.0001). Plains Sucker from unmodified water bodies demonstrated at most a minor change in performance between sampling periods (Battle Creek, p = 0.041; Caton Creek p = 0.068). The substantial energetic input into station holding may result in life history trade-offs impacting the populations’ continued existence in this part of its native range.


Edgar, M. (2022) The introduction of Cipangopaludina chinensis and tropic effects of sympatric freshwater fish invaders in southern Alberta reservoirs.

Thesis Title: The introduction of Cipangopaludina chinensis and tropic effects of sympatric freshwater fish invaders in southern Alberta reservoirs.

Author: Megan Edgar


At present, one of the most pervasive risks to freshwater ecosystems are invasive species. Invasive species are among the leading antagonists to global biodiversity, since they can out-compete or predate on native species which leads to changes of the structure of food webs and alteration of ecosystem function. As biogeographic boundaries are broken down by human-related means of spread, more are we seeing novel occurrences between non-native species and the ecosystems they are introduced to. As invasive species continue to radiate from their original regions, it is critical to understand how these species will impact their new ecosystems. As of 2019, non-native Chinese Mystery Snail (Cipangopaludina chinensis (Gray, 1834)) has persisted in McGregor Lake Reservoir, Alberta, Canada. Additionally, Northern Crayfish (Faxonius virilis) a non-native species which has expanded their range into lakes and rivers in Alberta, exists in sympatry with Chinese Mystery Snail in McGregor Lake Reservoir.

I aimed to advise management programs related to both Chinese Mystery Snail and Northern Crayfish in Alberta lakes and reservoir systems, and provide important information regarding the trophic interactions and outcomes to native recreational fish species (Northern Pike (Esox lucius), Walleye (Sander vitreus), and Lake Whitefish (Coregonus clupeaformis)).

In this thesis, I provide a comprehensive literature review regarding Chinese Mystery Snail in Canada, along with pertinent information regarding their impacts, life history characteristics, morphological characteristics, and range within invaded and native ranges. The initial finding of Chinese Mystery Snail is officially documented in Alberta, along with biological information that may aid management efforts. DNA barcoding is used to confirm the species identification and the barcode is added to GenBank. We analyze growth rate and fecundity, and assessed the presence of digenean trematode cercariae in snails in McGregor Lake Reservoir. After a 24-hour experimental period, we confirmed that Chinese Mystery Snail specimens are not infected by digenean trematodes. We also determine that shell growth quickly outpaces shell width, and that upon emergence Chinese Mystery Snail is larger than many of the native snail species in Albertan waterbodies. We also determine that Chinese Mystery Snail in Alberta produce a lower average number of juveniles compared to populations elsewhere. We also suggest that Chinese Mystery Snail meet four of the five stages of species invasion: arrival, establishment, growth, and reproduction, however there is no evidence of dispersal to adjacent waterbodies.

With the use of stable isotope analysis and gut content analysis, I address the trophic consequences that may arise with the addition of Northern Crayfish and Chinese Mystery Snail into aquatic ecosystems in southern Alberta, as well as their impacts to Northern Pike, Walleye and Lake Whitefish. I sampled five reservoirs in Alberta (St. Mary’s Reservoir, Forty-Mile Reservoir, Sherburne Lake Reservoir, Travers Lake Reservoir, and McGregor Lake Reservoir), collecting macrophytes, benthic macroinvertebrates, small-bodied fish species, as well as invasives and large recreational fish species. I hypothesized that the presence of only one aquatic invader would create bottom-up effects on the food-web, and that an additional invasive species would amplify these effects, creating shifts in fish trophic positions by moving basal energy away from higher trophic levels through the consumption of algae and macrophytes, or by providing a new prey resource. I also hypothesized that Chinese Mystery Snail and Northern Crayfish would have overlapping niches, through competition for resources or predation. Briefly, I determined that fish are becoming more piscivorous compared to reference lakes where there are no invasive species present, community trophic positions are higher in reservoirs where only Northern Crayfish are present as an invasive, and that carbon ranges are narrower in systems with only Northern Crayfish and wider when both invasives are in sympatry. A few reasons that these effects may be occurring to fish include an “adaptive lag” period, or lack of macrophytes in invaded waterbodies due to the invasives present. I also discovered that trophic niche ellipses of Chinese Mystery Snail and Northern Crayfish are overlapping, pointing to competitive exclusion.

The results from this thesis address my overall goals to investigate the introduction of Chinese Mystery Snail and the potential impacts of interactions between Chinese Mystery Snail and Northern Crayfish on native recreational fish species in reservoirs in southern Alberta. The findings gained throughout this thesis are useful for the management of both invasive species and will hopefully provide a catalyst for other researchers and resource managers.


Theis, S. (2022) Offsetting approved harmful anthropogenic impacts in the 21st century – Insights into global offsetting practices, habitat banking as an alternative offsetting mechanism and application of habitat enhancement in northern boreal lake systems.

Thesis Title: Offsetting approved harmful anthropogenic impacts in the 21st century – Insights into global offsetting practices, habitat banking as an alternative offsetting mechanism and application of habitat enhancement in northern boreal lake systems.

Author: Sebastian Theis


Land-use change via human development is a major driver of biodiversity and habitat area loss and ecosystem function impairment. To reduce these impacts, billions of dollars are spent on environmental offsets, aimed to compensate for authorized negative impacts. Studies evaluating offset project effectiveness and individual mechanisms, remain rare.

Chapter 2 aimed to address the persistent questions of whether high project compliance is synonymous with high functional success as well as how to address residual or chronic impacts in aquatic ecosystems which can occur after offset establishment, for example because of the ephemeral timescale of some projects through a systematic review process and meta-analysis. While compliance and function were related to each other, a high compliance score did not guarantee a higher degree of function. However, function did improve with larger projects, specifically when projects targeted productivity or specific habitat features, and when multiple complementary management targets were in place. Altogether these relationships highlight specific ecological processes that may help improve offsetting outcomes for the conservation of habitat and biodiversity. The meta-analysis for offsetting residual or chronic impacts yielded three main approaches; habitat creation; restoration and enhancement and biological manipulation. Habitat creation projects, mainly targeting salmonids, with a high pooled effect size (0.8) and biomass increase (x1.4) needs to be explored for other species had a pooled effect size. Habitat restoration projects targeted a wide range of species and communities with a pooled effect size of 0.66, and intermediate biomass increases (>1x). Biological manipulation had the lowest effect size (0.51) with effort outcomes being highly variable.

Conservation and mitigation banks are widely used alternative mechanisms to traditional offsetting to compensate for unavoidable negative environmental impacts from development. In Chapter 3 we utilized publicly available banking data from for the United States to test whether area ratio requirements were met as well as how well ecological equivalency was achieved and to model current and future bank reserves through a predictive modeling framework. We conclude that most bank transactions using Preservation, Enhancement, and Re-establishment targeting wetlands, species, or multiple Mitigation-Targets met No Net Loss requirements on a ratio base. Wetland transactions, making up most of all assessed transactions (n = 10628), still missed matching appropriate impact to offset types in 25% of all cases, mainly due to Preservation not leading to any additional habitat area gain.  While the Preservation of wetlands and the Rehabilitation of streams can provide a multitude of benefits, both practices need to be revised on an ecological level to bridge the gap between Not Net Loss based on credit and area yield ratios and ecological equivalence. Future predictions indicate a decrease in available reserves for banks targeting wetlands or multiple ecosystems, with potential bottlenecks relating to large reserves being limited to the Southeast and release schedules not catching up to the current and anticipated demand. Banks targeting species or streams are predicted to meet future demand, with species banks (conservation banks) following a different legislative and operational approach based on the listing of endangered species. Most current reserves for all four bank types are restricted to very few service areas with around one-third of all bank areas still awaiting release, limiting their availability on a broader scale.

Chapter 4 focussed on the introduction of coarse woody habitat in a northern boreal lake and responses of aquatic fish, invertebrate and macrophyte communities through a Bayesian modeling approach and the use of changes in beta diversity components over time. Catch data was collected over 2 years and posterior model predictions showed an increase in habitat use of the enhanced areas by resident fish (spottail shiner – Notropis hudsonius; northern pike – Esox lucius; white sucker – Catostomus commersonii; brook stickleback – Culaea inconstans), while no probable effect on overall fish health, measured in Relative Weight, was linked to the enhancements. Enhancement structures featured increased macrophyte and invertebrate richness and biomass compared to reference sites and pre-treatment assessments over the course of three years. Enhanced sites also retained improved richness (macrophytes), diversity (macroinvertebrates) and biomass (both), despite structural integrity loss of enhancements as early as 1 week post construction.


Pallard, J. (2022) Assessing the effects of non-native salmonids on Bull Trout (Salvelinus confluentus) in Alberta’s Rocky Mountain foothills.

Thesis Title:Assessing the effects of non-native salmonids on Bull Trout (Salvelinus confluentus) in Alberta’s Rocky Mountain foothills.

Author: Jacqueline Pallard


The rapid decline in global biodiversity threatens the natural resources, food security, health, and livelihoods of current and future generations. Anthropogenic activities, including the introduction of non-native species, habitat fragmentation and alteration, and resource extraction, have exacerbated this decline. One such imperiled species are Bull Trout (Salvelinus confluentus), which have exhibited significant declines throughout their range and are expected to decline by >30% over the next 21 years in Alberta. While their decline is attributed to a myriad of threats, the degree to which non-native fishes contribute to their decline is uncertain. The objective of my thesis was to investigate the effects of Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta), two non-native salmonids, on the habitat use and dietary niche of Bull Trout. To address the habitat component, I developed a multi-species N-mixture model using in-stream and land use derived characteristics to assess how Brook Trout and Brown Trout affect Bull Trout abundance in relation to habitat factors. I determined that Brook Trout negatively affect Bull Trout abundance when streams are <11°C and lack habitat complexity. Interactions between Brown Trout and Bull Trout are less certain, but larger, lower elevation streams are likely to see reductions in Bull Trout abundance where Brown Trout invasion is present and likely to occur. To address the dietary component, I employed stable isotope analysis to investigate how Brook Trout and Brown Trout interact with the dietary niche of Bull Trout. I determined that Bull Trout in sympatry with both Brook Trout and Brown Trout undergo a niche shift and are displaced from terrestrial-based resources. Furthermore, potential for competitive exclusion exists when resources are low given all species exhibit a high degree of niche overlap (>80%) when in sympatry and the amount of niche overlap does not decrease between allopatry and sympatry. The findings of my thesis suggest that both Brook Trout and Brown Trout interfere with the resource use of Bull Trout, on multiple levels, and provides practical guidelines for limiting future declines.


Roberts, K. N. (2022) The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Thesis Title: The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Author: Karling Roberts


Habitat offsets, where damages to natural ecosystems caused by socio-economic development projects are compensated for by the construction or restoration of ecosystems, can contribute to biological conservation when implemented properly. But, large uncertainties remain surrounding our ability to construct ecosystems that offer high quality habitat and sustainably provide desired ecosystem functions and services. Trophic structure and dynamics sustain ecosystem stability and function by limiting competition between consumers and alleviating prey species from damaging levels of predation. The application of food web theory has improved outcomes in ecological restoration and conservation, and has the potential to do the same for habitat offsetting. In this thesis I present one way trophic structure and seasonal trophic dynamics of an offset can be assessed, and examine how stable isotope analysis can be improved for use on sensitive species and in multi-season studies.

In the Alberta oil sands, unavoidable destruction of fish habitat from open-pit mining is offset with the construction of small lakes on or near mine sites. To investigate trophic structure in constructed offsets, I sampled the first offset lake constructed in the Alberta oil sands, Horizon Lake, and eight natural lakes for comparison. I measured stable carbon and nitrogen isotope ratios in the tissues of fish, and used these values to estimate metrics of trophic structure. I found that, despite the unique fish assemblage found in the offset lake, its trophic structure metrics are within the range of variation detected in natural lakes. The offset lake was most similar in terms of habitat to natural lakes that are relatively small and deep, but its trophic structure was more similar to large lakes with diverse fish assemblages. We recommend trophic structure continue to be examined in these and other offsets to further our understanding of their potentially unique ecology.

Seasonal variation in environmental conditions and resource availability may play an underappreciated role in the maintenance of biodiversity, especially in ecosystems that experience drastic seasonal changes. High-latitude and high-altitude aquatic ecosystems switch between an open water state in the summer and an ice covered state in the winter. This large environmental change is associated with reduced primary and secondary productivity, but it is not clear how consumers such as fishes respond. To address this knowledge gap, I examined the trophic dynamics of fish populations in three natural lakes and one constructed offset habitat. I used stable isotope analysis and stomach content analysis to assess if fish were 1) maintaining the same diet across seasons, 2) changing their diet seasonally, or 3) going dormant seasonally. We found that fishes most commonly change their diet between seasons in the three natural lakes and the offset. But, there was also evidence of diet maintenance and seasonal dormancy. Flexible foraging and a diversity of seasonal trophic responses among fish populations are likely contributing to the maintenance of biodiversity within these ecosystems. Evidence of winter activity by fishes in the offset is promising, and suggests the habitat is fulfilling its role as an over-wintering habitat for fishes.  

Stable isotope analysis is an important ecological method with many applications, but it often requires lethal sampling to obtain tissue samples. In addition, most stable isotope research is performed in the summer, leaving a gap in our understanding of whether isotope data collected in different seasons can be interpreted using the same methods. To address this, I investigated how lethal (muscle) and non-lethal (fin) tissues differ in their stable carbon and nitrogen isotope ratios, and whether inter-tissue differences change with season. I found that muscle and fin differ consistently in carbon and nitrogen stable isotope ratios, but whether season affects this relationship is species- and isotope-dependent. We recommend accounting for differences in tissue types whenever possible, and accounting for season of capture when research questions are highly sensitive to variation in isotope ratios.

Overall, this thesis demonstrates how ecological study of constructed offsets can advance our understanding of human modified ecosystems, basic ecological principles, and ecological methods. As offsetting grows as a practice across Canada and around the world, using these large-scale projects to further these objectives is imperative for improving the practice of offsetting and represents an enormous opportunity for advancing ecological research. 

Bazan, S. (2021) Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Thesis Title: Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Author: Sergio Bazan


During July 2021, 30 sampling sites at Bow River Watershed and 6 sampling sites at Crowsnest River were visited to perform tubifex relative abundance counts and the collection of environmental conditions associated to each site, such as stream characteristics, water physicochemical parameters, sediment composition and quality. Relative abundance of tubifex worms at Crowsnest River was significatively higher than any Hydrologic Unit 8 (HUC8) of Bow River Watershed except for Jumpingpound Creek (p-value 0.372). Higher relative abundance of tubifex worms were found in Jumpingpound Creek and Highwood River within Bow River watershed, but the difference with the other HUC8 was not statistically significant. The land use analysis results show higher relative abundance of tubifex worms around urban and farmland areas. However, the differences between all land use categories were not statistically significant (p-value 0.515), The same results were found for Silt-Clay type of sediments over of Granular sediments with no statistically significant difference (p-value 0.543). A multivariable linear model of tubifex relative abundance for the study area was built. The adjusted r-squared value was (R 2 = 0.1755). The variables included in the model were: the water pH, the wetted width, the stream velocity, the estimated flow, and the sediment classification. However, the assumption of linearity and homogeneity of variances were not meet by the proposed linear model.

Van Mierlo, V. (2021) Occupancy and Impacts of the Northern Crayfish (Faxonius virilis) in Tributaries of the North Saskatchewan River Basin.

Thesis Title: Occupancy and Impacts of the Northern Crayfish (Faxonius virilis) in Tributaries of the North Saskatchewan River Basin

Author: Victoria van Mierlo


Invasive species are the second greatest threat to biodiversity globally. Crayfish are especially robust invaders due to their omnivorous nature and ability to compete both directly (resource procurement) and indirectly (habitat occupation and modification) with native species. In the North Saskatchewan River (NSR) basin, the Northern Crayfish (Faxonius virilis) was introduced and has persisted since the early 1990s. Despite the North Saskatchewan River being an ecologically, economically, and culturally valuable watershed, the crayfish’s impacts on Alberta’s native fish communities have yet to be assessed.

We aimed to determine the in-stream environmental characteristics most associated with the crayfish’s occupancy in the North Saskatchewan River and determined which currently unoccupied tributaries are most prone to future invasion. We deployed 24-hour baited crayfish traps and collected environmental measurements (water temperature (°C), turbidity (NTU), flow velocity (ms-1), and physical complexity) at 37 tributary reaches along the Alberta portion of the North Saskatchewan River basin. Northern Crayfish were detected at 13 of 37 tributary reaches, with no occurrences detected west of Edmonton. Occupancy model selection and averaging revealed that water temperature alone drove occupancy of Northern Crayfish in tributaries of the North Saskatchewan River and that streams with mean summer water temperatures greater than 18.7 °C are 50% or more likely to be occupied by Northern Crayfish and thus, are at highest risk for subsequent invasion. Further, we found that streams with mean summer water temperatures below 15 °C were less than 25% likely to be or become occupied by Northern Crayfish. Cold water streams may have some natural protection against subsequent Northern Crayfish invasion.

We sampled ten North Saskatchewan River basin tributaries for F. virilis and six native common-generalist fish species and used stable isotope analysis to investigate if there is sharing of and/or exploitative competition for nutritional resources between F. virilis and native fish species. We also investigated if F. virilis sympatry was related to differences in fish isotopic characteristics and/or reduced condition of native fishes. Moderate overlap (13.8-40.2%) of F. virilis and native fishes’ fundamental isotopic niches indicated that F. virilis have the potential to consume the same resources as native fishes. However, overall segregation of realized isotopic niches indicated a lack of resource sharing between F. virilis and native fishes in NSR tributaries. Similarity between the Bayesian estimated realized standard ellipse areas (SEAB), carbon ranges, and body condition of F. virilis allopatric and sympatric native fish populations indicated that F. virilis sympatry did not have negative trophic effects on the native fish species in this study. Our results suggest that F. virilis may be utilizing dietary plasticity to exploit a slightly different trophic niche than native fishes and in doing so, avoid exploitative competition for nutritional resources. Dietary plasticity could facilitate the establishment and invasion of F. virilis populations in currently unoccupied tributaries of the North Saskatchewan River basin in the future.

The results from this thesis provide practical guidelines for watershed management of invasive Northern Crayfish populations in the North Saskatchewan River and Alberta. Our findings also highlight the importance for watershed managers to continue to prevent further spread of F. virilis in the North Saskatchewan River basin to prevent potential negative impacts on native fish while further research is conducted.

Hamilton, K. (2020) Streamflow is changing in rivers across Alberta: assessing regional variation in changing hydrologic indices.

Thesis Title: Streamflow is changing in rivers across Alberta: assessing regional variation in changing hydrologic indices.

Author: Kyle Hamilton


The flow regime is a crucial factor in the well-being of aquatic and riparian ecosystems. Many components of those ecosystems, ranging for nutrient transport to morphology, are impacted by various hydrologic parameters. The parameters help define and quantify five important hydrologic regime characteristics: magnitude, duration, timing, frequency, and rate of change. Our study utilized the Indicators of Hydrologic Alteration (IHA) indices to (1) determine how various ecologically relevant components of streamflow are changing across Alberta’s various biomes; and (2) examine the similarities and differences between streamflow trends and climate trends. The overarching goal of these objectives is to create a foundation upon which water management practices can be created or modified.

Region-specific water management is required to balance the residential, commercial, and industrial water needs of a particular region with ecological concerns and conservation initiatives. Understanding the trends in hydrologic parameters is an important step in recognizing the vulnerabilities of each region. Streamflow at Water Survey of Canada stations was assessed for linear trends using a Mann-Kendall Trend Analysis. Our approach of assessing overall trends on a regional basis was validated when looking at trends in magnitude. The average daily flow rate for spring and summer months was found to be decreasing in the boreal region but increasing in the grassland region. Other hydrologic indices were found to exhibit significant trends on a province-wide level. Annual minimum and maximum flow conditions over a variety of durations were observed to be merging across the province. Similarly, the rate of change of streamflow between consecutive days is decreasing across Alberta.

To determine whether these results were the function of climate oscillation patterns, a composite analysis was performed to determine the effect of the El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on hydrologic indices. Only 8% of parameters were found to be significantly influenced by PDO patterns and 4% influenced by ENSO patterns.

McPherson, M. (2020) Habitat use by fluvial Arctic Grayling (Thymallus arcticus) across life stages in northern mountain streams.

Thesis Title: Habitat use by fluvial Arctic Grayling (Thymallus arcticus) across life stages in northern mountain streams.

Author: Morag McPherson 


Northern aquatic ecosystems face increasing pressures from climate change and natural resource development, raising conservation concerns for species in these understudied regions.  The Arctic Grayling (Thymallus arcticus) is a widely distributed, but sensitive, northern freshwater fish that is a good indicator of general aquatic health. In the Northwest Territories (NWT), there has been little focus on studying riverine Arctic Grayling populations or their use of stream habitats within mountain river watersheds. The purpose of my research is to characterize fluvial Arctic Grayling distribution among mountain streams in the NWT, and to determine habitat characteristics and ecological factors that influence Arctic Grayling habitat use across life stages. Sampling sites (n=183) were selected in four sub-basins within the Little Nahanni River watershed in the southwest NWT. In the summer of 2015, each site (100 meters in length) was electrofished and stream habitat parameters were measured. Arctic Grayling were collected for biological analyses of age, size, weight, and reproductive development. Results showed shifts in Arctic Grayling development by size and age class that corresponded with shifts in distribution observed across the study streams. From these findings, four distinct post-emergence life stages for Arctic Grayling were identified: young-of-year (YOY), juvenile, sub-adult and adult. Step-wise logistic regression was used to explore the relationship between the occurrence of Arctic Grayling life stages and stream habitat characteristics. Multivariate regression tree (MRT) analysis was used to identify environmental thresholds and habitat-based life stage segregation, and redundancy analysis (RDA) was used to determine potential life stage-specific habitat correlations. Differences emerged in how Arctic Grayling life stages use habitat across a range of available stream conditions. YOY Arctic Grayling were found exclusively in low elevation, low gradient habitat dominated by silty-sand substrate with average water temperatures >10oC. Similarly, juvenile Arctic Grayling occupied low elevation, warm water stream habitat, but associated strongly with run habitats, as well as showing movement towards cooler water temperatures and more riffle dominated habitats. Sub-adult Arctic Grayling used the widest range of habitats across the study area, being found at a range of elevations and water temperatures, demonstrating the ability of this life stage to use a diversity of available habitats. Sub-adults showed a relationship to in-stream riffle, pool, and cascade-boulder habitats. Adults had a strong correlation to elevation and water temperature, using habitats with high elevation (>1200 m) and low temperature (7oC), and increased proportions of pool and boulder habitat. The four sub-watersheds studied provided distinct stream habitats and Arctic Grayling life stages separated across the habitat types, advancing our understanding of the life cycle habitat requirements for fluvial populations in mountain systems. It provides insight on the important and potential limiting factors, such as availability of warm water habitats, to population success in cold regions. The dynamic nature of Arctic Grayling habitat use in mountain streams highlights the need to consider habitat complexes at the watershed scale when defining species life stage requirements, managing habitats, monitoring populations, and assessing potential impacts into the future. Improved understanding of the distribution, habitat requirements and ecology of different life history types and life stages of Arctic Grayling is crucial for the effective management and monitoring of this species in northern environments