Trophic Structure of Apex Fish Communities in Closed Versus Leaky Lakes of Arctic Alaska

Despite low species diversity and primary production, trophic structure (e.g., top predator species, predator size) is surprisingly variable among Arctic lakes. We investigated trophic structure in lakes of arctic Alaska containing arctic char Salvelinus alpinus using stomach contents and stable isotope ratios in two geographically-close but hydrologically-distinct lake clusters to investigate how these fish may interact and compete for limited food resources. Aside from different lake connectivity patterns (‘leaky’ versus ‘closed’), differing fish communities (up to five versus only two species) between lake clusters allowed us to test trophic hypotheses including: (1) arctic char are more piscivorous, and thereby grow larger and obtain higher trophic positions, in the presence of other fish species; and, (2) between arctic char size classes, resource polymorphism is more prominent, and thereby trophic niches are narrower and overlap less, in the absence of other predators. Regardless of lake cluster, we observed little direct evidence of arctic char consuming other fishes, but char were larger (mean TL = 468 vs 264 mm) and trophic position was higher (mean TP = 4.0 vs 3.8 for large char) in lakes with other fishes. Further, char demonstrated less intraspecific overlap when other predators were present whereas niche overlap was up to 100% in closed, char only lakes. As hydrologic characteristics (e.g., lake connectivity, water temperatures) will change across the Arctic owing to climate change, our results provide insight regarding potential concomitant changes to fish interactions and increase our understanding of lake trophic structure to guide management and conservation goals

A Lota lota consumption: trophic dynamics of non-native Burbot in a valuable sport fishery

Unintentional and illegal introductions of species disrupt food webs and threaten the success of managed sport fisheries. Although many populations of Burbot Lota lota are declining in the species’ native range, a nonnative population recently expanded into Flaming Gorge Reservoir (FGR), Wyoming–Utah, and threatens to disrupt predator–prey interactions within this popular sport fishery. To determine potential impacts on sport fishes, especially trophy Lake Trout Salvelinus namaycush, we assessed the relative abundance of Burbot and quantified the potential trophic or food web impacts of this population by using diet, stable isotope, and bioenergetic analyses. We did not detect a significant potential for food resource competition between Burbot and Lake Trout (Schoener’s overlap index = 0.13), but overall consumption by Burbot likely affects other sport fishes, as indicated by our analyses of trophic niche space. Diet analyses suggested that crayfish were important diet items across time (89.3% of prey by weight in autumn; 49.4% in winter) and across Burbot size-classes (small: 77.5% of prey by weight; medium: 76.6%; large: 39.7%). However, overall consumption by Burbot increases as water temperatures cool, and fish consumption by Burbot in FGR was observed to increase during winter. Specifically, large Burbot consumed more salmonids, and we estimated (bioenergetically) that up to 70% of growth occurred in late autumn and winter. Further, our population-wide consumption estimates indicated that Burbot could consume up to double the biomass of Rainbow Trout Oncorhynchus mykiss stocked annually (\u3e1.3 × 105 kg; \u3e1 million individuals) into FGR. Overall, we provide some of the first information regarding Burbot trophic interactions outside of the species’ native range; these findings can help to inform the management of sport fisheries if Burbot range expansion occurs elsewhere

Quantitative PCR assays for detection of five Alaskan fish species: Lota lota, Salvelinus alpinus, Salvelinus malma, Thymallus arcticus, and Cottus cognatus from environmental DNA

The North Slope of Alaska contains arctic fish populations that are important for subsistence of local human populations, and under threat from natural resource extraction and climate change. We designed and evaluated four quantitative PCR assays for detection of environmental DNA from five Alaskan fish species present on the North Slope of Alaska: burbot (Lota lota), arctic char (Salvelinus alpinus), Dolly Varden (Salvelinus malma), arctic grayling (Thymallus arcticus), and slimy sculpin (Cottus cognatus). All assays were designed and tested for species specificity and sensitivity, and all assays detected target species from filtered water samples collected from the field. These assays will enable efficient and economical detection of the above species from lakes and rivers. This in turn will provide managers with improved knowledge of current distributions and future range shifts associated with climate and development threats, enabling more timely management

Investigating the Morphological and Genetic Divergence of Arctic Char \u3ci\u3e(Salvelinus alpinus)\u3c/i\u3e Populations in Lakes of Arctic Alaska

Polymorphism facilitates coexistence of divergent morphs (e.g., phenotypes) of the same species by minimizing intraspecific competition, especially when resources are limiting. Arctic char (Salvelinus sp.) are a Holarctic fish often forming morphologically, and sometimes genetically, divergent morphs. In this study, we assessed the morphological and genetic diversity and divergence of 263 individuals from seven populations of arctic char with varying length-frequency distributions across two distinct groups of lakes in northern Alaska. Despite close geographic proximity, each lake group occurs on landscapes with different glacial ages and surface water connectivity, and thus was likely colonized by fishes at different times. Across lakes, a continuum of physical (e.g., lake area, maximum depth) and biological characteristics (e.g., primary productivity, fish density) exists, likely contributing to characteristics of present-day char populations. Although some lakes exhibit bimodal size distributions, using model-based clustering of morphometric traits corrected for allometry, we did not detect morphological differences within and across char populations. Genomic analyses using 15,934 SNPs obtained from genotyping by sequencing demonstrated differences among lake groups related to historical biogeography, but within lake groups and within individual lakes, genetic differentiation was not related to total body length. We used PERMANOVA to identify environmental and biological factors related to observed char size structure. Significant predictors included water transparency (i.e., a primary productivity proxy), char density (fish·ha-1), and lake group. Larger char occurred in lakes with greater primary production and lower char densities, suggesting less intraspecific competition and resource limitation. Thus, char populations in more productive and connected lakes may prove more stable to environmental changes, relative to food-limited and closed lakes, if lake productivity increases concomitantly. Our findings provide some of the first descriptions of genomic characteristics of char populations in arctic Alaska, and offer important consideration for the persistence of these populations for subsistence and conservation

Quantitative PCR Assays for Detection of Five Arctic Fish Species: \u3ci\u3eLota lota\u3c/i\u3e, \u3ci\u3eCottus cognatus\u3c/i\u3e, \u3ci\u3eSalvelinus alpinus\u3c/i\u3e, \u3ci\u3eSalvelinus malma\u3c/i\u3e, and \u3ci\u3eThymallus arcticus\u3c/i\u3e from Environmental DNA

The North Slope of Alaska contains arctic fish populations that are important for subsistence of local human populations, and are under threat from natural resource extraction and climate change. We designed and evaluated four quantitative PCR assays for the detection of environmental DNA from five Alaskan fish species present on the North Slope of Alaska: burbot (Lota lota), arctic char (Salvelinus alpinus), Dolly Varden (Salvelinus malma), arctic grayling (Thymallus arcticus), and slimy sculpin (Cottus cognatus). All assays were designed and tested for species specificity and sensitivity, and all assays detected target species from filtered water samples collected from the field. These assays will enable efficient and economical detection and monitoring of these species in lakes and rivers. This in turn will provide managers with improved knowledge of current distributions and future range shifts associated with climate and development threats, enabling more timely management

The Abiotic and Biotic Controls of Arctic Lake Food Webs: A Multifaceted Approach to Quantifying Trophic Structure and Function

The Arctic is warming faster than any other region of the globe. To conserve and manage many thousands of lakes across arctic landscapes, scientists need to understand historic and present conditions within these lakes to predict how the lakes, and the organisms that inhabit them, may respond to a changing climate. The goal of my research was to improve our understanding of what physical, chemical, and biological factors contribute to: 1) how lake food webs are assembled; and, 2) how these food webs may change in the future. First, I used long-term observations and lab experiments to determine how fish food, including zooplankton and snails, may respond to a warming climate. I then used field measurements of arctic char (Salvelinus alpinus) body characteristics, genetic samples, and fish diets to investigate if, and potentially why, populations of arctic char across a series of lakes achieve different maximum body sizes. Finally, as a method of monitoring population-level changes of fish abundance, I collected samples of arctic char DNA in lake water to test if estimated arctic char population abundances within a given lake correspond to the amount of DNA collected. Fish will require more food to eat as their metabolism increases with warming lake temperatures. Based on a thirty-year period of record, I determined zooplankton abundance increases in warmer years, indicating there is likely to be enough food for fishes in the future. Accordingly, zooplankton and snail abundance and development was also faster in warmer treatments of my lab experiments. My field observations indicated these are important prey items for arctic char. Small arctic char eat more zooplankton and large arctic char eat more snails, and these observations were consistent whether or not other predators are found in the particular lake. Similarly, my analyses did not indicate morphological or genetic differences between small and large arctic char within the same lake, suggesting arctic char size structure is determine by biological characteristics, including primary productivity and arctic char density. Indeed, estimates of arctic char population abundances across a series of lakes followed a gradient of arctic char densities, and my DNA sampling corresponded with this gradient. As there are thousands of lakes across the Arctic, my research demonstrates lake food webs, and the fishes within them, are likely to adapt to a warming climate. However, biological, chemical, and physical properties of these lakes can vary widely such that management and conservation plans may need to be developed at relatively small spatial scales across a large landscape

At the forefront: evidence of the applicability of using environmental DNA to quantify the abundance of fish populations in natural lentic waters with additional sampling considerations

Environmental DNA (eDNA) sampling has proven to be a valuable tool for detecting species in aquatic ecosystems. Within this rapidly evolving field, a promising application is the ability to obtain quantitative estimates of relative species abundance based on eDNA concentration rather than traditionally labor-intensive methods. We investigated the relationship between eDNA concentration and arctic char (Salvelinus alpinus) abundance in five well-studied natural lakes, and additionally, we examined the effects of different temporal (e.g., season) and spatial (e.g., depth) scales on eDNA concentration. Concentrations of eDNA were linearly correlated with char population estimates (〖"R " 〗_"adj" ^"2" = 0.78) and exponentially correlated with char densities (〖"R " 〗_"adj" ^"2" = 0.96 by area; 0.82 by volume). Across lakes, eDNA concentrations were greater and more homogeneous in the water column during mixis; however, when stratified, eDNA concentrations were greater in the hypolimnion. Overall, our findings demonstrate that eDNA techniques can produce effective estimates of relative fish abundance in natural lakes. These findings can guide future studies to improve and expand eDNA methods while informing research and management using rapid and minimally invasive sampling.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author