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Passive acoustic telemetry provides an important tool to study the spatial ecology and behaviour of organisms in marine and freshwater systems, but understanding the detection range of acoustic receivers is critical for interpreting acoustic data and establishing receiver spacing to maximize study efficiency. This study presents a comprehensive review of how acoustic detection range has been considered and assessed to date, summarizes important variables to monitor when determining the detection range of a receiver array, and provides recommendations to account for detection range during experimental design, analysis and data interpretation. A total of 378 passive acoustic telemetry studies (1986–2012) were scored against a set of pre-defined criteria to provide a standardized assessment of how well detection range was accounted for, from a maximum possible score of 45. Scores ranged from 0 to 39 (11.1 ± 0.4; mean ± 1 SE). Over the past decade mean scores have been consistently between 6.7 and 12.9 which indicates that detection range has not been adequately considered in most contemporary acoustic telemetry studies. Given the highly variable nature of detection range over space and time, it is necessary to create a culture of detection range testing among the scientific community. For robust telemetry studies it is recommended that consideration of detection range should be given a greater focus within study design, execution and data analysis. To aid array design in new systems, short-term detection range tests should be conducted in the most representative area of the study system prior to deployment. As well, fixed distance sentinel tags should ideally be deployed at a representative receiver site within the array to provide a continuous assessment of detection range and influential environmental parameters should be monitored to facilitate modeling of detection range variability over time. When warranted, data analysis should incorporate modeled variation in detection ranges.

Stable isotope analysis is widely used to quantify the flow of energy, nutrients, and biomass through aquatic food webs, where values of carbon (δ 13 C) and nitrogen (δ 15 N) have been used to estimate littoral carbon use (LCU) and trophic position (TP) in lentic ecosystems, respectively. Standardizing stable isotope values with these metrics allows for comparison across different systems and time scales; however, several equations to quantify LCU and TP have been introduced with little guidance on the bias and limitations of each equation, or how and when different equations should be used. Here, we provide recommendations on the appropriate use of LCU and TP equations in freshwater ecosystems based on our analysis of case studies using five fish species common to the study lakes. We address three common challenges of ecosystem variability, namely (1) temporal, (2) spatial, and (3) differing rates of tissue turnover between study and baseline organisms. We begin with a relatively simple case study (Parry Sound) then explore challenges around spatial (Lake Erie) and temporal (Canoe Lake) variation, and the use of multiple fish tissue types (Canoe Lake). We found LCU and TP estimates to be highly variable and dependent on the equation used. High percentages of individual fish exhibited unrealistic LCU values, and the equation of LCU used had a large effect on calculated TP values. We found relative littoral carbon use (LCU R ) produces the most consistent TP estimate, avoiding extreme values while reflecting the natural variability of the system. We propose a framework for calculating LCU and TP, allowing researchers to produce the least amount of bias relative to the known feeding ecology of study species while making estimates comparable across systems. Based on our case studies, we have developed a decision tree to guide researchers in estimating LCU and TP in freshwater ecosystems.

Winter is a challenging period for aquatic research—weather is uncomfortable, ice is hazardous, equipment fails, and daylength is short. Consequently, until recently relatively little research on freshwater fishes has included winter. Telemetry methods for tracking fish and observing movement behavior are an obvious solution to working in harsh conditions because much of the data can be collected remotely, and passive methods collect data year-round without winter maintenance. Yet, many telemetry studies do not collect data during winter or, if they do, only report data from the ice-free seasons while the remaining data are unused. Here, we briefly summarize the advantages and limitations of using telemetry methods in winter, including acoustic and radio telemetry and passive integrated transponder technology, then review the range of questions related to fish ecology, behavior, bioenergetics, and habitat use that can be addressed in winter using telemetry. Our goals are to highlight the untapped potential of winter fish biology and to motivate scientists to revisit their four-season telemetry data and incorporate objectives specific to winter biology in future study plans.

Prey selection can influence interactions among species, the composition and abundance of prey, and ultimately the movement of energy within the ecosystem. Different species of the exploited coral trout Plectropomus spp. often co-occur in reef environments, but their foraging behaviour and ecological niches are largely unknown. To explore niche overlap and resource use of sympatric adult coral trout, stable isotopes (δ13C and δ15N) were quantified for 3 tissues (muscle, red blood cells, and plasma) collected between August 2013 and February 2014 from P. leopardus (n = 117) and P. laevis (n = 36) at 4 reefs in eastern Australia. Bayesian standard ellipses were used to show that prey selection of P. leopardus varied considerably from P. laevis, particularly from P. laevis in the blue-spot colour phase. Size of adult individuals had little influence on δ13C and δ15N values for P. leopardus and both footballer and blue-spot colour phases of P. laevis. Spatio-temporal comparisons of P. leopardus trophic positions, made by adjusting baseline algae and planktonic δ15N at each reef and sampling period, demonstrated that trophic positions varied in time and space, and warrants further investigation. This study highlights that sympatric species of coral trout have distinct ecological roles and will likely react differently to environmental disturbances and/or changes in habitat or prey composition.

There is little doubt that Arctic ecosystems will continue to face unprecedented change in the coming decades. The identification of food web structures that confer stability to these systems is, therefore, a priority. Here, we use stable isotopes and fatty acids to resolve the food web structure of a seasonally ice-covered fjord (Cumberland Sound, Baffin Island, Canada) sampled in late summer. We show that the food web is structured such that upper trophic levels couple separate energy channels (based on phytoplankton or macroalgae), a previously documented food web structure that has been linked with stability in temperate ecosystems, but never established in a seasonally dynamic, ice-covered ecosystem. Herbivorous zooplankton (e.g. Calanus hyperboreus) relied exclusively on phytoplankton, whereas herbivorous benthos used either phytodetritus (e.g. Hiatella arctica) or macroalgae (e.g. Tectura testudinalis), supporting the existence of separate energy channels. Upper trophic level fishes and marine mammals relied more heavily on phytoplankton- than macroalgal-derived carbon (58 to 100% reliance on phytoplankton), but 6 out of 8 species sampled derived energy from both carbon sources. Since benthic invertebrate predators used both phytodetrital- and macrolgal-based resources, the coupling of separate energy channels was also iterated within the benthos. The temporally pulsed nature of phytoplankton production, characteristic of Arctic seas, indicates that Arctic consumers also act as couplers of resources in time because phytoplankton- and detrital-based carbon would likely reach upper trophic levels earlier and later in the season, respectively. Potential changes in the relative production of macroalgae and phytoplankton under climate change scenarios could impact the stability-promoting food web structure reported here.

With climate change resulting in unpredictable sea ice conditions between years, it is crucial to gain a more comprehensive understanding of the subsequent effects on Arctic marine ecosystems. Arctic cod ( Boreogadus saida ) play a key role in the Arctic marine food web, serving as a food source that is estimated to contribute up to 75 % of energy transfer to higher trophic levels. To investigate Arctic cod residency and distribution in Resolute Bay (74°44′N, 095°04′W), 85 individuals from four locations in the bay were captured, measured, weighed, implanted with acoustic tags and subsequently tracked on an acoustic array of 49 receivers. Two main periods of residence in the bay were identified, the first in open water and the second under ice cover, and both concluded with a collective mass departure of fish. A generalised linear mixed model was used to investigate the influence of variables on Arctic cod presence/absence in the bay, indicating that ingress and egress were influenced by environmental changes, particularly those associated with the transition from open-water to the ice-covered period. Timing and distribution, during the study period, appeared to be influenced by a combination of physiological acclimation, and a balance between resource availability and refuge from predators. Receiver site Residence Index (RI) analysis revealed strong site fidelity of fish towards the northern areas of the bay, and this behaviour was consistent between tagging groups and individuals, indicating that the majority of tagged cod were representative of a single school. This study represents the first employment of acoustic telemetry to monitor the movements of individual Arctic cod over 9 months, incorporating both open-water and ice-covered periods.

Polar bears (Ursus maritimus) are apex predators of the Arctic, which exposes them to an array of natural and anthropogenic stress factors. Metabolomics analysis profiles endogenous metabolites that reflect the response of biological systems to stimuli, and the effects of multiple stressors can be assessed from an integrated perspective. A targeted, quantitative, liquid chromatography–mass spectrometry-based metabolomics platform [219 metabolites including amino acids, biogenic amines, acylcarnitines, phosphatidylcholines (PCs), sphingomyelins, hexoses (Hex), and fatty acids (FAs)] was applied to the muscle and liver of polar bears from the Southern and Western Hudson Bay (Canada) subpopulations (SHB and WHB, respectively). Multivariate statistics were then applied to establish whether bears were discriminated by sex and/or subpopulation. Five metabolites identified by variable importance projection (VIP) discriminated the hepatic profiles of SHB males and females (Hex, arginine, glutamine, one PC, one sphingomyelin), while fifteen metabolites (primarily PCs along with leucine) contrasted the livers of males from SHB and WHB. Metabolite profiles in the muscle of male and female bears could not be differentiated; however, the muscles of SHB and WHB males were discriminated primarily by PCs and FAs. Stable isotope ratios (δ13C and δ15N) were variably related to metabolites; δ13C was correlated with some VIP metabolite concentrations, particularly in comparisons of male bears from SHB and WHB, suggesting an influence of dietary differences. However, δ15N and age exhibited few, relatively weak correlations with metabolites. The metabolite profiles discriminating the sexes and subpopulations may have utility for future assessments regarding the effects of specific stressors on the physiology of Hudson Bay polar bears.

Arctic cod (Boreogadus saida (Lepechin, 1774)) vertically segregate by size class in deep waters, but such dynamics had not been explored in shallow waters. Spatial distribution of Arctic cod was investigated in Resolute Bay, Nunavut, Canada (74°41N, 94°52W) from 20 July to 5 August 2012, using a combination of hydroacoustic survey and direct capture. Hydroacoustic surveys identified two high concentrations of Arctic cod, with larger individuals detected on the west side, and smaller individuals on the east. Catch data confirmed size segregation, with fish sampled on the west side of the bay significantly larger (mean = 174 mm total length (TL); 35.9 g weight (WT)) than those on the east (mean = 110 mm TL; 9.2 g WT). Fish density on the west was estimated at 3.52 fish·m −2 , extrapolated to the full 0.52 km 2 of the surveyed shoal to ∼1 830 400 fish and 65 711 kg (assuming a 35.9 g mean WT). Smaller fish on the east side were more abundant (9.32 fish·m −2 ; total abundance ∼11 836 400 fish or 108 894 kg; mean WT = 9.2 g). Horizontal habitat-partitioning was observed between Arctic cod size classes over a small geographic area (∼8 km 2 ), most probably due to partitioned resources and to mitigate predation risk.

To examine the influence of diet and age on organochlorine contaminant (OC) concentrations in two closely related ringed seal (Phoca hispida) populations enantiomeric fractions (EFs) of chiral contaminants and stable isotopes of nitrogen (delta15N) and carbon (delta13C) were measured along with OCs in ringed seals collected from the east and west side of the Northwater Polynya. Seals from these two locations were feeding at the same trophic level based on delta15N values in muscle but had slightly different sources of carbon based on delta13C measurements in muscle. After removing the influence of age, sex, and blubber thickness, OC concentrations did not vary between ringed seals from the east and west side of the polynya. SigmaPCB, SigmaDDT, and Sigmachlordane were found to increase with age for both male and female seals. The inclusion of older (>20 years) female seals, which may have a reduced reproductive effort, may influence the relationships in females. Stable isotopes failed to describe OC concentrations in ringed seals suggesting that diet was not a major factor in variation of OC concentrations within this ringed seal population. Cis- and trans-chlordane, oxychlordane, and heptachlor epoxide were all nonracemic in the ringed seal blubber but did not vary with age, sex, or collection site. Alpha-HCH appeared racemic (enantiomeric fraction = 0.50 +/- 0.01) in the seals, although this EF is different than those previously observed in their prey species, and was found to vary significantly with age. EF values in the ringed seals varied considerably from other Arctic marine mammals and seabirds, providing addition evidence that the type(s) and characteristic(s) of the enzymes involved in biotransformation of chiral OCs vary between these organisms.

As apex marine predators, seabirds are often sampled to monitor bioaccumulative persistent organic pollutants (POPs) in the marine environment. Despite the restrictions on use and production of many POPs, concern remains about levels of these chemicals present in marine biota due to their potential toxicity. Many seabird species are migratory, and although overwintering area has been hypothesized to affect the accumulation of POPs, few have studied the contribution of exposure in the wintering area on the POP burdens of seabirds. This study investigated the impact of wintering area on concentrations and patterns of organochlorines (OCs) and polybrominated diphenyl ethers (PBDEs) in plasma of breeding great skuas Stercorarius skua from 3 colonies; Bjørnøya (Svalbard), southeast Iceland and Shetland (Scotland). To do so, stable isotope values of primary feathers grown during the winter were used in conjunction with geolocator data (n = 16) to assign untracked individuals (n = 122), to 3 wintering areas (America, Europe and Africa). Birds wintering in Africa had lower plasma concentrations of many OCs and PBDE 47 compared to the other areas. Nevertheless, the influence of wintering area differed between contaminants and between breeding colonies. We conclude that although wintering area had a significant effect on both concentrations and patterns of POPs, its influence was small in comparison to differences in exposure to these pollutants at breeding colonies, but that accumulation of POPs during the winter may be important for specific populations of seabirds.