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Arctic surface air temperatures have been warming at twice the global rate, making it one of the most susceptible regions to current climate change. Effects on cold-adapted aquatic species, such as the culturally and ecologically important Arctic charr (Salvelinus alpinus), are difficult to anticipate and may vary depending on site-specific attributes. Temperature has a direct influence on aspects of species’ fitness, including growth, reproduction and, ultimately, survival. Previous research on temperature-growth patterns in Arctic charr has yielded variable results, particularly for studies observing these patterns in the wild. Two field-based studies are presented in this thesis, in an attempt to better understand temperature-growth patterns for wild populations of Arctic charr. In the first study, individual measurements of annual, or within-season growth were determined from tag-recaptured Arctic charr and examined in relation to summer sea surface temperatures and within-season capture timing in the Ungava and Labrador regions of eastern Canada. Differences in among-year growth were significant for Ungava Bay Arctic charr, with growth being positively correlated with temperature. Growth of Labrador Arctic charr did not vary significantly among years. Regional comparisons demonstrated that Ungava Arctic charr had significantly higher annual growth rates, with differences among years in all regions being positively correlated with temperature. Within-season growth rates of Labrador Arctic charr peaked in June, declined toward August, and were negatively correlated with the length of time spent at sea and mean experienced sea surface temperatures. A quadratic model relating growth rate to temperature best explained the pattern of within-season growth. The higher annual growth of Ungava Bay Arctic charr was attributed to the high sea surface temperatures experienced in 2010-11 and the localized differences in nearshore productivity as compared to Labrador. Results suggest that increases in water temperature may have profound consequences for Arctic charr growth in the Canadian sub-Arctic, depending on the responses of local marine productivity to those same temperature increases. In the second study, oxygen stable isotope temperature reconstruction methods were used to estimate mean experienced summer temperatures from growth zones within individual otoliths of Arctic charr sampled from contrasting lake environments. For either lake, otolith-estimated temperatures were not significantly related to back-calculated growth. Significant negative effects on back-calculated growth were observed due to increasing air temperatures in the smaller lake, owing to warmer surface waters and a limited amount of preferred cool-water habitat available. A similar relationship was not observed in the larger lake, indicating that the cooler, deeper lake provides ample preferred cool-water habitat for Arctic charr despite climate warming. In addition, young-of-the-year temperatures negatively related to zone 2 growth for the smaller lake, whereas no significant correlation was found for the larger lake. Results here provide evidence for differing climate-influenced growth outcomes depending on the site-specific fish density: preferred thermal habitat volume ratio as dictated by local attributes including lake morphometry, upstream catchment area and life-history strategy. Conclusions from this thesis include the increased need for detailed site- and population-specific assessments of the impacts of increasing temperatures on Arctic charr growth. Better understanding of the drivers of temperature-growth relationships in wild Arctic charr populations will facilitate more accurate stock forecasts with the overall goal of sustaining exploited Arctic charr populations as the climate warms and becomes increasingly variable.

Abstract The thesis includes two studies of Arctic charr, Salvelinus alpinus, responses to climate variation. In the first chapter, site-specific data from a fishery on the Hornaday River, Northwest Territories (NWT), are used to make inferences about the environmental drivers of observed variation in the mean biological characteristics of the catch. Mean length and weight characteristics of subsistence-fished Arctic charr available from 15 years of monitoring on the Hornaday River, were significantly influenced by among-year differences in local summer temperature and/or precipitation patterns. Environmental influences on mean length were age-specific, with temperature being the most important influence on younger (age-5) fish and precipitation being the most important influence on older (age-8) fish. Mean weight was positively influenced by precipitation only. Significant models of length-temperature relationships further indicated that larger mean sizes occurred in years when average summer air temperatures ranged from 6.7-7.1ºC. The effects of precipitation on nutrient exports to the nearshore marine area appear to trigger many of the observed correlations. Overall, results suggest that the large-scale environmental changes predicted by climate change scenarios will hold significant implications for Arctic charr from the Hornaday River, with population-specific effects likely to be exhibited in other northern Arctic charr populations. The second chapter uses archival biological data on 67 anadromous and lacustrine charr populations from eastern North America to assess variation within and among populations of Arctic charr as a function of latitude. Eastern North America was defined to include areas east of 80° W, including: Maine, the Canadian Maritime Provinces, insular Newfoundland, Labrador, Québec, and the eastern Arctic Islands of Baffin, Devon and Ellesmere. Obtained population data sets contained individual observations on age, length, weight, sex and fecundity of Arctic charr from as many age-classes as possible and included sufficient life-history information to permit grouping populations to life-history types: dwarf lacustrine, normal lacustrine and anadromous. Data were used to determine the significance of latitudinal clines in the biological responses as explanations of variation in age-specific biological characteristics (length and growth rate) among populations and life-history-types. The presence of a gradient in temperature and growing season length across latitudes was significantly related to a latitudinal compensation in the growth rate of all age-classes of normal and dwarf lacustrine Arctic charr populations. No decrease in dwarf length-at-age along the gradient was noted, whereas normal lacustrine length-at-age in the younger ages (age-4 to age-6) declined along the gradient. Results provide evidence of the applicability of the countergradient hypothesis as an explanation of among population differences in length-at-age for normal and dwarf lacustrine Arctic charr. Only weak evidence of the applicability of the countergradient hypothesis to anadromous Arctic charr populations was found. Although a decrease in length-at-age for all age-classes was observed along the gradient, only four age-classes (age-10 to age-13) showed a significant increase in growth rate with an increase in latitude. The similarity of the marine thermal environment across the latitudinal gradient is argued to account for the differential response of anadromous Arctic charr in comparison to lacustrine populations.

Abstract The thesis includes two studies of Arctic charr, Salvelinus alpinus, responses to climate variation. In the first chapter, site-specific data from a fishery on the Hornaday River, Northwest Territories (NWT), are used to make inferences about the environmental drivers of observed variation in the mean biological characteristics of the catch. Mean length and weight characteristics of subsistence-fished Arctic charr available from 15 years of monitoring on the Hornaday River, were significantly influenced by among-year differences in local summer temperature and/or precipitation patterns. Environmental influences on mean length were age-specific, with temperature being the most important influence on younger (age-5) fish and precipitation being the most important influence on older (age-8) fish. Mean weight was positively influenced by precipitation only. Significant models of length-temperature relationships further indicated that larger mean sizes occurred in years when average summer air temperatures ranged from 6.7-7.1ºC. The effects of precipitation on nutrient exports to the nearshore marine area appear to trigger many of the observed correlations. Overall, results suggest that the large-scale environmental changes predicted by climate change scenarios will hold significant implications for Arctic charr from the Hornaday River, with population-specific effects likely to be exhibited in other northern Arctic charr populations. The second chapter uses archival biological data on 67 anadromous and lacustrine charr populations from eastern North America to assess variation within and among populations of Arctic charr as a function of latitude. Eastern North America was defined to include areas east of 80° W, including: Maine, the Canadian Maritime Provinces, insular Newfoundland, Labrador, Québec, and the eastern Arctic Islands of Baffin, Devon and Ellesmere. Obtained population data sets contained individual observations on age, length, weight, sex and fecundity of Arctic charr from as many age-classes as possible and included sufficient life-history information to permit grouping populations to life-history types: dwarf lacustrine, normal lacustrine and anadromous. Data were used to determine the significance of latitudinal clines in the biological responses as explanations of variation in age-specific biological characteristics (length and growth rate) among populations and life-history-types. The presence of a gradient in temperature and growing season length across latitudes was significantly related to a latitudinal compensation in the growth rate of all age-classes of normal and dwarf lacustrine Arctic charr populations. No decrease in dwarf length-at-age along the gradient was noted, whereas normal lacustrine length-at-age in the younger ages (age-4 to age-6) declined along the gradient. Results provide evidence of the applicability of the countergradient hypothesis as an explanation of among population differences in length-at-age for normal and dwarf lacustrine Arctic charr. Only weak evidence of the applicability of the countergradient hypothesis to anadromous Arctic charr populations was found. Although a decrease in length-at-age for all age-classes was observed along the gradient, only four age-classes (age-10 to age-13) showed a significant increase in growth rate with an increase in latitude. The similarity of the marine thermal environment across the latitudinal gradient is argued to account for the differential response of anadromous Arctic charr in comparison to lacustrine populations.

Mercury concentrations in freshwater and marine biota are an ongoing concern, even in areas remote from local point sources, such as in the Canadian Arctic and sub-Arctic. Anadromous Arctic charr, which feed in the marine environment, have lower mercury concentrations than non-anadromous Arctic charr, which feed strictly in freshwater, but the two life-history forms have rarely been studied together, and the mechanisms driving the difference are unclear. Here, data from nine pairs of closely-located anadromous and non-anadromous Arctic charr populations were used to explore the impact of biological and life-history factors on individual total mercury concentration ([THg]) across a range of latitudes (49 – 81° N) in eastern Canada. From six of these sampling locations, additional samples of lower trophic level biota (i.e., algae, invertebrates, and forage fishes) were obtained in order to investigate patterns of total mercury (THg) and methylmercury (MeHg) biomagnification in the marine and lacustrine foodwebs supporting Arctic charr. Arctic charr mean [THg] ranged from 20 to 114 ng/g wet weight (ww) in anadromous populations, and was significantly higher in non-anadromous populations (all p < 0.01), ranging from 111 to 227 ng/g ww. Within-population variations in Arctic charr [THg] were best explained by fish age, and were also positively related to fork-length and δ15N-inferred trophic level. Across all sampling sites, the relationship between Arctic charr [THg] and fish age was significant and statistically similar in both life-history types, but only the non-anadromous fish demonstrated a significant relationship with trophic level. Fork-length and site latitude did not explain significant additional variation in Arctic charr [THg] across sampling locations. Trophic magnification factors were 1.98 – 5.19 for THg and 3.02 – 6.69 for MeHg in lacustrine foodwebs, and 1.59 – 2.82 for THg and 2.72 – 5.70 for MeHg in marine foodwebs, and did not differ significantly between the two feeding habitats for either THg or MeHg. The biomagnification rate of MeHg exceeded that of THg in both habitats. Mercury concentrations at the base of the foodweb were higher in the lacustrine environment (estimated at 17 – 139 ng/g dw for THg and 5 – 42 ng/g dw for MeHg) than in the marine environment (8 – 39 ng/g dw for THg and 1 – 11 ng/g dw for MeHg). The proportion of mercury in the methylated form was related to trophic level, and the relationship was statistically similar in the lacustrine and marine habitats. There was no effect of site latitude on mercury concentrations in marine or lacustrine biota, thus the difference between feeding habitats was consistent across a range of latitudes (56 – 72°N) in eastern Canada. We conclude that a difference in prey mercury concentration, driven by differential mercury concentrations at of the base of the lacustrine and marine foodwebs, is important for explaining the difference in mercury concentration between anadromous and non-anadromous in Arctic charr.

I examined phenotypic and genetic variation in growth traits in 30 families of commercial Fraser strain Arctic charr (Salvelinus alpinus) reared in freshwater (FRW) and brackish water (BRW) in Eastern Canada. I detected family by treatment interactions for all traits [body weight (BW), condition factor (K) and specific growth rate (SGR)] across all measurement dates and growth intervals, however, mean family BW in FRW was correlated phenotypically with BRW BW. In addition, FRW fish showed significantly greater survival than those transferred to BRW and fish which survived until the conclusion of the experiment were significantly heavier in BW at the baseline assessment than their full-sibs that died. These observations suggest that BW in FRW and BW in BRW should be analyzed as separate but correlated traits in Arctic charr breeding programs. I then tested the potential for genetic improvement in this species by calculating genetic parameters for BW and K, and tested if previously identified quantitative trait loci (QTL) for these traits were detectable across the broodstock. QTL with experiment-wide and chromosome-wide significance for body size and condition factor were detected on multiple linkage groups. Heritability for BW and K was moderate in FRW (0.29-0.38) but lower in BRW (0.14-0.17). Genetic correlations for BW across environments were positive and moderate (0.33-0.67), however equivalent K correlations were weaker (0.24-0.37). This information was then used to predict the rate of genetic change following one generation of selection for BW using phenotypic selection and genomic methodologies including marker-only selection and marker assisted selection. The greatest response in the rate of genetic change was achieved by selecting only from families in which significant BW QTL had been identified. As such, marker assisted selection showed the greatest gain in genetic response with 5.4% in FRW and 4.3% in BRW. These results have applications to commercial aquaculture as the Canadian aquaculture industry is attempting to diversify with alternative species. Such genetic improvement strategies will aid in developing a strain of Arctic charr characterised by increased BW. / Funding provided through the NSERC Strategic grants program. The project was sponsored by CanAqua Seafoods Ltd. in collaboration with the Coastal Zones Research Institute.

Le mercure, polluant toxique pour les êtres vivants est présent dans tous les compartiments de l'environnement. Son cycle biogéochimique est encore mal connu, et des lacunes existent, notamment dans les sites de hautes altitudes comme les Alpes françaises. Au cours de ces travaux, nous avons examiné la dynamique du mercure dans les écosystèmes lacustres alpins, par l'étude du transfert de ce polluant entre les différents réservoirs que sont la neige (bassin versant), l'eau des lacs, et les poissons. Par des échantillonnages réguliers (janvier à juin 2009) de la neige de surface du lac Bramant, nous montrons que le manteau neigeux est le siège de processus de dépôts atmosphériques de mercure et de méthylmercure provenant des sources anthropiques de la région de Grenoble. Nous montrons également qu'une proportion de ces espèces rejoint le lac notamment lors de la fonte du manteau neigeux. Cependant, elles s'avèrent rapidement évacuées du lac en raison d'un fort et rapide renouvellement de ces eaux. Par ailleurs, la caractéristique spécifique (peu de végétation, grande minéralité) de ces bassins versants d'altitude explique également les faibles quantités de mercure présentes dans ces lacs. La faible contamination en mercure retrouvée dans les poissons de ces lacs est certainement due notamment à un faible temps de séjour du mercure dans l'eau. Enfin, grâce à un outil de prédiction et d'aide à la décision (WARMF), nous suggérons que les paramètres essentiels gouvernant la méthylation du mercure et la contamination des poissons dans nos lacs ne sont pas les dépôts atmosphériques mais plutôt les caractéristiques physico-chimiques du lac et de son bassin versant.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Increases in global temperatures resulting from climate change have raised concern over potential responses of Arctic charr, <i>Salvelinus alpinus</i>, a cold-adapted freshwater/anadromous fish species in the salmonid family. While various aspects of adult Arctic charr ecology are well established, juvenile, and in particular, young-of-the-year (YOY) ecology is less well understood. The study of early life stages is important because of implications for subsequent population dynamics as well as their particular sensitivity to climate change. In this thesis, I aimed to broaden the scope of knowledge on juvenile Arctic charr from Canadian populations with a particular emphasis on YOY, and thermal habitat use through four studies. An intensive study of juvenile Arctic charr from Lake Hazen, Nunavut, demonstrated a preference during the summer for stream environments, particularly those fed by warm upstream ponds. Charr occupying both stream and nearshore lake habitats were found to feed similarly, with chironomids occurring most frequently in diets. Some older stream-dwelling charr preyed on smaller, younger Arctic charr. Preferred stream occupancy is likely mediated by physical barriers created mainly by water velocity, and by distance from the lake, lake-ice dynamics, low water depth, and turbidity. Water velocities and possibly intercohort competition resulted in stream habitat segregation by size, with YOY mainly found in low velocity pools and back eddies adjacent to stream banks, but not in water velocities greater than 0.1m/s. Greatest charr densities in streams were found in small, shallow, slow-flowing side channels, which are highly susceptible to drought. A discriminant function analysis model based on carbon and nitrogen stable isotope values was used to identify offspring of piscivorous large-form and non-piscivorous small-form Arctic charr morphotypes from Lake Hazen, Nunavut. The adult morphotypes were estimated to contribute approximately equally to the YOY population, however, the morphotype offspring were differentially distributed among sampled nursery sites. Unequal distribution corresponds with prerequisites suggested for the evolution of trophic specialists within a single population that experiences assortative mating based on trophic specialization. An assessment of growth rates and otolith-inferred metabolic rates obtained from YOY from 23 populations over a 27˚ latitudinal gradient demonstrated latitudinal variability consistent with countergradient variation where northern populations demonstrated faster growth and higher metabolic rates compared to southern populations. Countergradient variation (CGV) is defined as genetic variation that counteracts the negative influences of the physical environment, minimizing phenotypic variability along a gradient. Otolith-inferred metabolic rates from free-living animals reflect the average daily energy expenditure of the organism, which incorporate the energetic costs of standard metabolic rate (SMR) and other processes such as feeding, locomotion, thermoregulation, reproduction and growth. As such, variations in otolith-inferred metabolic rates may reflect a combined increase in feeding, activity and SMRs in northern populations. Nevertheless, the phenotypic variation in physiological traits observed here demonstrates the significant adaptability of Arctic charr to different thermal regimes with different growing season lengths. Otolith-inferred temperatures and fork lengths at capture from YOY from two proximal fluvial and lacustrine sites in Labrador were used to compare growth and thermal habitat use between habitat types. Otolith-inferred temperatures were not significantly correlated with air temperatures, suggestive of behavioural thermoregulation by YOY at both sites. The majority of YOY from Kogluktokoluk Brook (fluvial) were found using temperatures consistent with laboratory determined preferred temperatures for juvenile Arctic charr, whereas most Tom’s Pond (lacustrine) YOY were found using temperatures ranging between preferred temperatures and optimal temperatures for growth. Otolith-inferred temperatures were only correlated to fork lengths in Tom’s Pond YOY. The lack of correlation in Kogluktokoluk Brook YOY may reflect resource partitioning occurring as a result of territoriality known to occur among stream salmonids. The limited range of temperatures used by fluvial YOY in this study, particularly the lack of cooler temperatures, suggests that fluvial YOY may face barriers to accessing thermal refugia, and as a result may be particularly vulnerable to climate change. Examining the ecology of juvenile Arctic charr from Canadian populations over a number of spatial scales (i.e. latitudinal, regional and local) highlighted the considerable phenotypic plasticity demonstrated by the species. While physiological plasticity observed over the latitudinal gradient reflected the ability for juvenile Arctic charr to utilize different thermal regimes, the regional comparison between habitat types demonstrated that the ability for juvenile Arctic charr to respond to climate change is likely to vary between habitat types. Further, on a local scale, behavioural plasticity was observed, but was found to be influenced by several regulatory factors. The study of the ecology of juvenile Arctic charr in this thesis has highlighted various factors affecting juvenile Arctic charr in Canada: temperature, water velocity, cover, maternal influences, habitat type and ration. The relative contributions of these factors as well as others which were not directly testable in this thesis (e.g. variability in standard metabolic rate, the role of genetic adaptation) are likely to vary with latitude, populations and habitat types. Deciphering the relative roles of these factors will allow better predictions of responses to climate change.