Aaron T. Fisk’s research while affiliated with University of Windsor and other places

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Publications (33)


Evidence of shifts in habitat use of two snappers (Lutjanidae) in a tropical estuarine bay subjected to seasonal upwelling
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January 2025

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33 Reads

Marine Ecology Progress Series

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AT Fisk

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ABSTRACT: Biological and environmental conditions are drivers of fish habitat use, making it essential to understand how fish move and use specific areas to inform effective fisheries management and conservation. This study quantified the residency and habitat use patterns of the juveniles and early adults of 2 commercially exploited snappers (Lutjanidae) in Santa Elena Bay, a tropical estuarine embayment influenced by a seasonal upwelling in the north Pacific coast of Costa Rica. Using an array of 28 acoustic receivers, we monitored 14 Colorado Lutjanus colorado (28.848.9 cm) and 16 Pacific dog L. novemfasciatus (22.5–49.3 cm) snappers over 22 mo. Both species were detected inside the bay over 60 % of the monitoring days, showing higher relative abundance in mangrove and transitional estuarine habitats. Throughout the study, a shift in habitat use was observed for both species. Individuals moved from mangrove and transitional habitats to the outer reef habitat and exhibited a decreasing occurrence probability over time, suggesting they leave the bay as they mature. Season and environmental variables, e.g. temperature, had minimal or no effect on the occurrence of the tracked snappers in the bay. However, roaming varied seasonally, increasing during upwelling periods. These results suggest that habitat connectivity facilitates gradual life stage transitions, indicating that Santa Elena Bay likely supports essential fish habitat for commercially important species, particularly for L. novemfasciatus. Results also highlight the importance of integrating knowledge of the complex interplay of biological components (e.g. developmental and intra- and interspecific interactions) and seasonal habitat dynamics into conservation and management strategies.



Full acoustic telemetry array, spanning 45.7 km, to monitor native and invasive fish connectivity in Canada's historic Rideau Canal Waterway. Receivers were deployed during the navigation season, from mid-May to mid-October, during 2019–2021. Each circle denotes an individual acoustic receiver, colour-coded to be reach-specific. Arrows point to each lockstation (LD) and the Rideau Ferry bridge, which delineates Big Rideau Lake (Reach 1) and Lower Rideau Lake (Reach 2). Water flows in the northeasterly direction. LD1 and LD7 serve as the southern and northern termini, respectively. Reach designations are as follows with colour designations in parentheses: Reach 1—LD1 to Rideau Ferry bridge (salmon); Reach 2—Rideau Ferry bridge to LD2 (pale blue); Reach 3—LD2 to LD3 (green); Reach 4—LD3 to LD4 (yellow); Reach 5—LD4 to LD5 (orange); Reach 6—LD5 to LD6 (teal); Reach 7—Edmonds LD6 to LD7 (purple); Reach 8—LD7 downstream (pink). We documented fish passages at all LDs in our telemetry array except LD1. Information about each LD and reach can be found in Tables 1 and 2. A map of the full 202 km Rideau Canal Waterway, including details of the study area in terms of the full system, and enlarged images of our acoustic array can be found in Figs. SA1 and SA5–SA7. Map projection: NAD 1983. Inset base map source: Government of Canada 1:250 000 NTS maps.
Enlarged acoustic telemetry array at, and images of, LD6 (Edmonds LD). Although each LD in the system varies, most are analogous to the one shown here. Navigation locks at each LD in our telemetry array were monitored each year from 2019 to 2021 for fish passages. (A) Acoustic receiver array at LD6 to evaluate connectivity and fish residency near infrastructure. The circles denote individual receivers, with blue circles indicating receivers deployed upstream (Reach 6) and purple circles indicating receivers deployed downstream (Reach 7) of LD6. The LD6 Dam was monitored by receivers in 2019 and 2020, though not all dams had coverage during our study due to equipment constraints. The fish symbols, located in the lock channels (usually calmer, sheltered areas), denote release locations that 60% of fish were transported to for surgical implantation of acoustic tags during poor weather conditions that created an unstable environment on our vessel. Map projection: NAD 1983. (B) The LD6 Lock chamber as water levels are being lowered. The lock gates in the image are the downstream gates. Note the hand cranks on the gate, which lockmasters use to manually operate the lock. (C) LD6 has a 167 m long and 4.1 m high stone arch dam consisting of a 96 m overflow stone weir and a 7.5 m long waste-weir of stacked logs. The dam creates a slackwater section to the upstream double-flight LD5. There are no fish pass systems in place at LDs in the Rideau Canal Waterway, making navigation locks the most plausible upstream connectivity pathway.
Abiotic information (left panels) and fish passage data for acoustically tagged northern pike and largemouth bass (right panels). Black rhombuses with a solid line, grey rhombuses with a fine-dotted line, and white rhombuses with a thick-dotted line represent the 2019, 2020, and 2021 navigation seasons, respectively. The navigation season each year in the Rideau Canal Waterway runs from mid-May to mid-October. Discharge rate (m³/s), lockage frequency, and (water) temperature (°C) data, averaged bi-weekly, are provided in the left panels. Discharge rates were highest in spring 2019. Lockage frequency and water temperature followed similar trends each year, peaking in July and August, though there were less lockages in 2020 as a result of COVID-19 lockdowns and restrictions. Cumulative passages for largemouth bass and northern pike are provided by month in the right panels. Northern pike conducted the most passages, with a peak number of passages (n = 9) in June 2019. No acoustically tagged-common carp passages were recorded and, therefore, this species was not included in the figure. No passages were recorded in 2021.
Boxplots illustrating the relationship between passage direction (D = downstream; U = upstream) and abiotic variables, including (water) temperature (°C), lockages, and discharge (m³/s), for northern pike and largemouth bass. Our results suggest that during the navigation season, fishes move upstream across lockstations more often during periods of warmer temperatures and higher lockage frequencies. Individuals passed upstream when discharge rates were <10 m³/s (P = 0.054). Both northern pike and largemouth bass showed similar responses to abiotic variables. Boxes represent the boundaries of the upper and lower quartiles, lines inside boxes represent medians, and whiskers represent the minimum and maximum values from the raw data.
Relationship between mean residency index (RI) at infrastructure approaches for acoustically tagged fishes (invasive common carp, and native northern pike and largemouth bass) in the Rideau Canal Waterway for the 2019 and 2020 navigation seasons (2021 not included due to equipment constraints). Residency was evaluated at five areas: the downstream dam approach (DD), the downstream lock approach (DL), the upstream dam approach (UD), the upstream lock approach (UL), and areas >200 m from infrastructure classified as “away” (A). All three species showed highest affinities for areas away from infrastructure, with overall low RI values near infrastructure (<0.20). Bars represent standard error. See Interspecific differences in LD residence, and Interspecific differences in fish residency with infrastructure and potential anthropause effects, for RI analysis methods and a discussion on findings, respectively. See Fig. SA12 and Table SA3 for changes in residency by year and RI ± SE for each species, at each approach area, during each navigation season.

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Ecological connectivity of invasive and native fishes in a historic navigation waterway
  • Article
  • Publisher preview available

February 2024

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44 Reads

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1 Citation

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Valerie Minelga

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Regulated waterways, interconnected by navigation barriers (locks and dams), are uniquely difficult to manage, given interest in enabling native species connectivity while minimizing invasions. Canada's historic Rideau Canal Waterway, a 202 km navigable route located in eastern Ontario and connected by 24 lockstations, embodies this challenge. The lock(s) and water-control dam that compose each lockstation may respectively offer a connectivity pathway, though to what extent is unclear. We used acoustic telemetry (native largemouth bass (Micropterus nigricans) and northern pike (Esox lucius), and invasive common carp (Cyprinus carpio); n = 224) to evaluate fish connectivity relative to lock operations and environmental data over three years (2019–2021). Thirty-five passages by 23 native fishes were recorded, with 49% of passages through locks. No common carp passages were detected; movements indicate that they favour higher flow areas downstream of dams, regions with no pathway upstream. Most passages were downstream and, of concern to obligate upstream migrators, we found that multi-flight and higher-lift locks appear impassable to upstream movements. Our results suggest that these lockstations limit, but not entirely restrict, connectivity.

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Changing environmental conditions have altered the feeding ecology of two keystone Arctic marine predators

August 2023

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196 Reads

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4 Citations

Environmental change in the Arctic has impacted the composition and structure of marine food webs. Tracking feeding ecology changes of culturally-valued Arctic char ( Salvelinus alpinus ) and ringed seals ( Pusa hispida ) can provide an indication of the ecological significance of climate change in a vulnerable region. We characterized how changes in sea ice conditions, sea surface temperature (SST), and primary productivity affected the feeding ecology of these two keystone species over a 13- and 18-year period, respectively, in northern Labrador, Canada. Arctic char fed consistently on pelagic resources (δ ¹³ C) but shifted over time to feeding at a higher trophic level (δ ¹⁵ N) and on more marine/offshore resources (δ ³⁴ S), which correlated with decreases in chlorophyll a concentration. A reduction in Arctic char condition factor and lipid content was associated with higher trophic position. Ringed seals also shifted to feeding at a higher trophic level, but on more pelagic resources, which was associated with lower SST and higher chlorophyll a concentrations. Years with abnormally high SSTs and reduced sea ice concentrations resulted in large isotopic niche sizes for both species, suggesting abrupt change can result in more variable feeding. Changes in abundance and distribution of species long valued by the Inuit of Labrador could diminish food security.


Seasonal variation in trophic structure and community niche dynamics of an Arctic coastal community of marine vertebrates

August 2023

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204 Reads

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2 Citations

Temporal variation in food web structure is widespread among highly seasonal environments, such as the Arctic and is driven by changes in resource availability. Variation in resource availability can lead to species differences in diet composition, isotopic niche width, and trophic position (TP) across seasons. Here, we used tissue samples that represent two distinct turnover rates for diet (liver = shorter-term, muscle = longer-term) from 18 fish and three marine mammal species to investigate seasonal (i) variation in TPs within the Southampton Island marine ecosystem of Hudson Bay, (ii) variation in consumer isotopic niche width within this part of the food web, and (iii) variation in community niche dynamics among a fish and marine mammal community using stable carbon (δ13C) and nitrogen (δ15N) isotope analyses. Many zooplanktivores and piscivores increased in TP in summer (i.e. shorter-term turnover period), whereas benthic-feeders dependent on ice-obligate prey decreased in TP. Most isotopic niche widths and community metrics (δ15N range, total ellipse area, mean centroid distance) were higher in liver than muscle. Our findings demonstrate seasonal changes in TPs, which suggests that Arctic communities may be differentially affected by longer ice-free periods and earlier onset of primary production due to accelerated climate change.


Lingering Effects of Legacy Industrial Pollution on Yellow Perch of the Detroit River

June 2023

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42 Reads

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1 Citation

Environmental Toxicology and Chemistry

We used yellow perch (Perca flavescens) captured at four sites differing in legacy industrial pollution in the Lake St. Clair–Detroit River system to evaluate the lingering sublethal effects of industrial pollution. We emphasized bioindicators of direct (toxicity) and indirect (chronic stress, impoverished food web) effects on somatic and organ-specific growth (brain, gut, liver, heart ventricle, gonad). Our results show that higher sediment levels of industrial contaminants at the most downstream Detroit River site (Trenton Channel) are associated with increased perch liver detoxification activity and liver size, reduced brain size, and reduced scale cortisol content. Trenton Channel also displayed food web disruption, where adult perch occupied lower trophic positions than forage fish. Somatic growth and relative gut size were lower in perch sampled at the reference site in Lake St. Clair (Mitchell's Bay), possibly because of increased competition for resources. Models used to determine the factors contributing to site differences in organ growth suggest that the lingering effects of industrial pollution are best explained by trophic disruption. Thus, bioindicators of fish trophic ecology may prove advantageous to assess the health of aquatic ecosystems. Environ Toxicol Chem 2023;42:2158–2170. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Abstract Stable isotope analysis at Trenton Channel, Detroit River, where polyaromatic hydrocarbon and polychlorinated biphenyl sediment contamination is highest, revealed trophic disruption compared with other sites in the Lake St. Clair–Detroit River system.


Estimating survival probabilities of Cambridge Bay Arctic char using acoustic telemetry data and Bayesian multistate capture–recapture models

August 2022

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82 Reads

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1 Citation

Arctic fishes are threatened by climatic change and other anthropogenic stressors, yet information on how such changes impact survival remains scarce. Acoustic telemetry has become valuable for studying aspects of fish ecology, including survival, which is invaluable in understanding potential responses to changing conditions. In Cambridge Bay, NU, we have been using acoustic telemetry to study movements and habitat use of the culturally and commercially important Arctic char (Salvelinus alpinus). Here, we combine acoustic telemetry data and Bayesian multistate mark–recapture models to study the survival of Arctic char from 2014 to 2018 in the region in freshwater and marine/estuarine habitats. We found that survival probabilities were high (>0.87) and models considering two environments (freshwater and marine) perform better than those considering three (including estuarine habitats). Furthermore, the survival in fresh water was higher than survival in marine/estuary environments. Overall, the results of this study further our understanding of important demographic parameters (i.e., survival) for Arctic char in the region, which will be useful in refining fishery management plans for the largest commercial fishery for this species in Canada.


Technoscience and the modernization of freshwater fisheries assessment and management

August 2022

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196 Reads

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7 Citations

Environmental Technology & Innovation

Inland fisheries assessment and management are challenging given the inherent complexity of working in diverse habitats (e.g., rivers, lakes, wetlands) that are dynamic on organisms that are often cryptic and where fishers are often highly mobile. Yet, technoscience is offering new tools that have the potential to reimagine how inland fisheries are assessed and managed. So-called “technoscience” refers to instances in which science and technology unfurl together, offering novel ways of spurring and achieving meaningful change. This paper considers the role of technoscience and its potential for modernizing the assessment and management of inland fisheries. It first explores technoscience and its potential benefits, followed by presentation of a series of synopses that explore the application (both successes and challenges) of new technologies such as environmental DNA (eDNA), genomics, electronic tags, drones, phone apps, iEcology, and artificial intelligence to assessment and management. The paper also considers the challenges and barriers that exist in adopting new technologies. The paper concludes with a provocative assessment of the potential of technoscience to reform and modernize inland fisheries assessment and management. Although these tools are increasingly being embraced, there is a lack of platforms for aggregating these data streams and providing managers with actionable information in a timely manner. The ideas presented here should serve as a catalyst for beginning to work collectively and collaboratively towards fisheries assessment and management systems that harness the power of technology and serve to modernize inland fisheries management. Such transformation is urgently needed given the dynamic nature of environmental change, the evolving threat matrix facing inland waters, and the complex behaviour of fishers. Quite simply, a dynamic world demands dynamic fisheries management; technoscience has made that within reach.



Feeding habits of Baffin Bay polar bears (Ursus maritimus): insight from stable isotopes and total mercury in hair

October 2021

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293 Reads

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7 Citations

Marine Ecology Progress Series

Loss of sea ice brought on by climate change affects polar bear Ursus maritimus access to prey. Here we investigated variation in feeding habits of the Baffin Bay (BB) polar bear subpopulation in relation to sea ice, habitat use, season, and demography using hair carbon (δ ¹³ C), nitrogen (δ ¹⁵ N), and sulfur (δ ³⁴ S) stable isotope values and total mercury (THg) concentrations as ecological tracers. We analyzed hair samples from BB polar bears (n = 131) of all age and sex classes live-captured in West Greenland during the spring in 2009-2013. BB polar bears occupied a narrow isotopic space, suggesting limited variation in carbon sources and trophic position within the subpopulation. THg concentrations (median ± SE: 5.1 ± 0.2, range: 0.3-12.5 µg g ⁻¹ dry weight, DW) were related to age class, and nearly half exceeded the suggested threshold for neurological effects in polar bears at 5.4 µg g ⁻¹ DW. Although distinct coastal and offshore space-use strategies have been reported for BB polar bears, our results suggest that both strategies lead to similar carbon sources and trophic positions. We found seasonal variation in δ ¹³ C and δ ³⁴ S across both space-use strategies, with δ ³⁴ S suggesting that all BB polar bears may prey on a higher proportion of benthic-feeding bearded seals Erignathus barbatus in late summer relative to spring. Despite wide fluctuations in inter-annual sea ice conditions and differences in space-use strategies among individuals, stable isotope values and THg concentrations suggested limited variation in feeding habits among BB polar bears. The variation of habitat tracers (δ ¹³ C and δ ³⁴ S) was related to season, whereas trophic tracer (δ ¹⁵ N and THg) variation was driven by demographic group. The specialized BB polar bear diet suggests limited feeding plasticity under continued climate warming.


Citations (24)


... The entire food web relied on Mysis and to a lesser extent Diporeia, highlighting the importance of these species and the critical need for continued monitoring as Diporeia density declined 59 % from 2003 to 2016 at 25 historical nearshore sampling stations (Mehler et al., 2018). Wegher et al. (2025) showed that within-species regional and depth-dependent differences in benthic and pelagic prey resource use and trophic position vary across Lake Superior fishes, with a difference of a full trophic position or greater being observed for the same species in the same region collected at different depths. Reliance on benthic prey resources increased with depth, but piscivores were primarily reliant on pelagic energy pathways due to, again, the high reliance on Mysis within the Lake Superior fish community. ...

Reference:

Lake Superior: Current conditions, trends, and emerging threats – Foreword to the special section
Regional variability of resource use, trophic position and habitat coupling within Lake Superior
  • Citing Article
  • October 2024

Journal of Great Lakes Research

... Apart from changes in diet and habitat loss, Arctic top predators will likely face an increasing number of anthropogenic pressures, such as increased noise and pollution from shipping, plastic pollution, increasing disease and parasite occurrence, (Kovacs and Lydersen, 2008;Merkel et al., 2021). Top predators have been shown to sometimes adapt to the change in diet (e.g., Yurkowski et al., 2016b;Vihtakari et al., 2018;Sauser et al., 2023), although not always successfully, as changes in prey quality, notably fat content, would affect species fitness (e.g., Descamps et al., 2022;Anderson et al., 2023;Sauser et al., 2023). The decline of iconic marine mammals in the Arctic is a major conservation concern, with implications for biodiversity and cultural ecosystem services in the Arctic. ...

Changing environmental conditions have altered the feeding ecology of two keystone Arctic marine predators

... While spatial heterogeneity is key in facilitating species coexistence (Stein et al., 2014;Barton et al., 2024), temporal heterogeneity may also play a pivotal role in this process through various niche-based mechanisms (Fretwell, 2020;White and Hastings, 2020). Seasonal changes in ecologically relevant characteristics impact resource availability (McMeans et al., 2015;Fuirst et al., 2023) and alter biotic interactions (Williams et al., 2017), thereby affecting organisms both directly and indirectly. Thus, to cope with seasonal changes in abiotic and biotic conditions (e.g., changes in environmental favorability, or quality and quantity of available food sources and habitats), many species were shown to exhibit temporal changes along certain axes of their realized niche breadth, which can also influence their niche overlap patterns (Albrecht and Gotelli, 2001;Roy and Thomas, 2003;Houadria and Menzel, 2020). ...

Seasonal variation in trophic structure and community niche dynamics of an Arctic coastal community of marine vertebrates

... Teleost fishes are particularly suitable neurotoxicity models, in part, because they exhibit widespread adult neurogenesis, allowing for lifelong brain growth (Zupanc 2008). The potential of fish brain size as a useful endpoint to assess sublethal neurotoxic effects of contaminants is supported by our recent observation of reduced brain size with exposure to legacy industrial pollution in yellow perch (Yin-Liao et al. 2023). Moreover, brain size is recognized as a biologically significant screen of neurotoxicity in neuropathology (Bolon et al. 2013). ...

Lingering Effects of Legacy Industrial Pollution on Yellow Perch of the Detroit River
  • Citing Article
  • June 2023

Environmental Toxicology and Chemistry

... We posit that combined sibship-abundance estimation datasets could further advance empirical support for predictive metapopulation models because the methodology has different strengths and constraints compared to methods using individual tagging and telemetry methods. Individual tagging and telemetry methods provide a wide range of approaches for quantifying movement and survival (Lucas and Baras 2000;Pine et al. 2003;Thorstad et al. 2013) and international collaborations (Iverson et al. 2018) and innovations in technoscience (Cooke et al. 2022) are continuously advancing the potential of these methods. However, making inferences from tagged individuals requires careful management of tagging and handling effects. ...

Technoscience and the modernization of freshwater fisheries assessment and management
  • Citing Article
  • August 2022

Environmental Technology & Innovation

... High network connectivity is a hallmark of microbiota resilience (130)(131)(132)(133), so such results might indicate a healthy fish population. Interestingly, Arctic char stock and survival in Ekaluktutiak were relatively stable (112,134,135). Thus, Ekaluktutiak gills microbiota exhibited a resilient pattern that involved mainly active strains belonging to Proteobacteria and Bacteroidetes (Table S3A; Fig. 7). ...

Estimating survival probabilities of Cambridge Bay Arctic char using acoustic telemetry data and Bayesian multistate capture–recapture models

... Stable isotopes analysis has been the primary tool to examine dietary patterns related to distinct coastal and offshore movement patterns within polar bear subpopulations (Blévin et al., 2020;Boucher et al., 2019;Rogers et al., 2015;Stern et al., 2021), but multiple methods are recommended to ensure reliable diet information (Bowen & Iverson, 2013). Stern et al. (2021) detected no differences between coastal and offshore adult female BB polar bears in hair sample carbon, nitrogen, and sulfur stable isotope values and total mercury concentrations. ...

Feeding habits of Baffin Bay polar bears (Ursus maritimus): insight from stable isotopes and total mercury in hair
  • Citing Article
  • October 2021

Marine Ecology Progress Series

... Hooded seals have undergone significant changes in phenology of their movements, with earlier departures north and delayed departures southward (see Case Study No. 3), resulting in an extended period of Arctic residency. Summer foraging migrations of ringed seals (Pusa hispida) to preferred seaice concentrations start at similar times compared to the past, but now require longer travel distances compared to decades ago (Freitas et al., 2008;Lone et al., 2019;Ogloff et al., 2021). ...

Long-distance movements and associated diving behaviour of ringed seals (Pusa hispida) in the eastern Canadian Arctic

... Winter is a challenging time for freshwater fishes, as water temperatures fall below thermal optima, icecover reduces light penetration, and food becomes scarce. Winter conditions can also provide cold, thermally stable habitats (e.g., 4 °C) where warmwater species lay dormant while cool-and coldwater species actively forage (Block et al. 2020;Marsden et al. 2021). For juvenile freshwater drum, water temperatures ≤ 1 °C may disorient individuals and lead to high mortality (Bodensteiner and Lewis 1992). ...

Using untapped telemetry data to explore the winter biology of freshwater fish

Reviews in Fish Biology and Fisheries

... High network connectivity is a hallmark of microbiota resilience (130)(131)(132)(133), so such results might indicate a healthy fish population. Interestingly, Arctic char stock and survival in Ekaluktutiak were relatively stable (112,134,135). Thus, Ekaluktutiak gills microbiota exhibited a resilient pattern that involved mainly active strains belonging to Proteobacteria and Bacteroidetes (Table S3A; Fig. 7). ...

Annual survival probabilities of anadromous Arctic Char remain high and stable despite interannual differences in sea ice melt date