Telemetry is increasingly being used to estimate population-level survival rates. However, these estimates may be affected by the detectability of telemetry tags and are reliant on the assumption that telemetry data represent the movements of the tagged fish. Predation on tagged fish has the potential to bias survival estimates, and unlike the issue of detectability, methods to correct for the resulting bias (termed "predation bias") are not yet developed. In an acoustic telemetry study on inner Bay of Fundy Atlantic salmon (Salmo salar) smolts during 2008 and 2011, unusual tag detection patterns were indicative that some data may have been representative of the movements of predators rather than smolts. To incorporate predation effects into the resulting survival estimates, a suite of 11 summary migration metrics were compared between Atlantic salmon smolts and striped bass (Morone saxatilis). Cluster analyses revealed that 2.4% to 13.6% of tags implanted in smolts exhibited migration patterns more similar to striped bass than to other smolts, which was interpreted here as evidence of predation. Reassigning the fate of these tags as "depredated-died" reduced estimated survival from 43.5% to 41.1% in 2008 and from 32.6% to 19.0% in 2011 relative to a traditional mark-recapture model, illustrating the effect of predation bias in this case study.Résumé : L'utilisation de la télémétrie pour estimer les taux de survie à l'échelle de la population est de plus en plus répandue. Ces estimations peuvent toutefois être influencées par la détectabilité des étiquettes utilisées et reposent sur le principe que les données de télémétrie rendent compte des déplacements des poissons marqués. La prédation de ces derniers pourrait cependant biaiser les estimations des taux de survie et, contrairement au problème de détectabilité, il n'existe pas encore de méthode permettant de corriger le biais qui en résulte (appelé « biais de prédation »). Dans une étude de télémétrie acoustique portant sur des saumoneaux de saumon atlantique (Salmo salar) de la haute baie de Fundy, menée en 2008 et 2011, des motifs de détection d'étiquettes inhabituels indiquaient que certaines données pouvaient refléter les déplacements de prédateurs plutôt que ceux des saumoneaux. Afin d'intégrer les effets de la prédation dans les estimations des taux de survie en découlant, 11 paramètres sommaires associés à la migration de saumoneaux de saumon atlantique et de bars d'Amérique (Morone saxatilis) ont été comparés. Des analyses typologiques ont révélé que de 2,4 % à 13,6 % des étiquettes implantées dans des saumoneaux témoignaient d'habitudes migratoires plus semblables à celles de bars d'Amérique qu'à celles d'autres saumoneaux, ce qui a été interprété comme une preuve de prédation. La réaffectation du destin de ces étiquettes à des individus « morts-victimes de prédation » s'est traduite par une réduction des taux de survie estimés de 43,5 % à 41,1 % pour 2008, et de 32,6 % à 19,0 % pour 2011, par rapport aux résultats d'un modèle de marquage-recapture tra...

Summary The field of acoustic telemetry has evolved rapidly and now permits the remote sensing of animal behaviour, movement, physiology and survival in environments, and species not previously possible. However, an inability to detect when a telemetered animal is consumed by a predator can complicate accurate interpretation of the telemetry data. In this paper, we describe the efforts taken to test the two generations of a novel prototype acoustic telemetry transmitter designed specifically to detect predation. Testing involved either staged predation events where tagged prey (Rainbow Trout Oncorhynchus mykiss and Yellow Perch Perca flavescens) were fed to captive Largemouth Bass Micropterus salmoides, or false‐positive testing where prey fish were tagged and held without the risk of predation. Metrics of interest were (i) the rate of correctly identifying the predation events, (ii) signal lag (i.e. the time required to detect a predation event), (iii) tag retention time in the predator's gut, and (iv) the rate of false‐positive triggering in both live and dead prey fishes. Staged predation events were successfully identified in 61/65 and 52/55 trials for generation 1 and 2 tags, respectively. Signal lag time was reduced in generation 1 tags (generally between 1 and 9 h) relative to generation 2 (3–29 h); although signal lag was highly variable. A generalized linear mixed model (GLMM) indicated strong evidence that signal lag and tag retention were both negatively correlated with water temperature, but were not affected by prey species and only slightly by individual predator traits. There was preliminary evidence that prey size may be an important determinant of both signal lag and tag retention. False‐positives in live fish were absent after 120 days for generation 1 tags (n = 31), however, the false‐positive rates were significantly higher (10/44) after only 66 days for generation 2 tags. False‐positives in dead fish showed that 20% of the generation 2 predation tags would falsely trigger 2–3 days post‐mortem. Testing of the novel predation tags was encouraging, however, further testing is recommended. Predation tags will be an important contribution to the field of acoustic telemetry, thus, permitting the improved data interpretation and less‐subjective estimates of predation rates in biotelemetry studies.

Background: Acoustic telemetry is an increasingly common method used to address ecological questions about the movement, behaviour, and survival of freshwater and marine organisms. The variable performance of acoustic telemetry equipment and ability of receivers to detect signals from transmitters have been well studied in marine and coral reef environments to inform study design and improve data interpretation. Despite the growing use of acoustic telemetry in large, deep, freshwater systems, detection efficiency and range, particularly in relation to environmental variation, are poorly understood. We used an array of 90 69-kHz acoustic receivers and 8 sentinel range transmitters of varying power output deployed at different depths and locations approximately 100-9500 m apart for 215 days to evaluate how the detection efficiency of acoustic receivers varied spatially and temporally in relation to environmental conditions. Results: The maximum distance that tags were detected ranged from 5.9 to 9.3 km. Shallow tags consistently had lower detection efficiency than deep tags of the same power output and detection efficiency declined through the winter months (December-February) of the study. In addition to the distance between tag and receiver, thermocline strength, surface water velocity, ice thickness, water temperature, depth range between tag and receiver, and number of fish detections contributed to explaining variation in detection efficiency throughout the study period. Furthermore, the most significant models incorporated interactions between several environmental variables and tag-receiver distance, demonstrating the complex temporal and spatial relationships that exist in heterogeneous environments. Conclusions: Relying on individual environmental variables in isolation to interpret receiver performance, and thus animal behaviour, may be erroneous when detection efficiency varies across distances, depths, or tag types. As acoustic telemetry becomes more widely used to study ecology and inform management, it is crucial to understand its limitations in heterogeneous environments, such as freshwater lakes, to improve the quality and interpretation of data. We recommend that in situ range testing and retrospective analysis of detection efficiency be incorporated into study design for telemetry projects. Furthermore, we caution against oversimplifying the dynamic relationship between detection efficiency and environmental conditions for the sake of producing a correction that can be applied directly to detection data of tagged animals when the intended correction may not be justified.

Acoustic telemetry is a useful tool to monitor the estuarine survival and behaviour of Atlantic salmon postsmolts. Most frequently, survival is reported as the static fraction of tagged postsmolts detected, and while the timing or location of mortality may be reported, covariates of survival or the relationship between migratory behaviour and survival are less often described. In this study, we used acoustic telemetry to follow Atlantic salmon smolts migrating to sea from four rivers in Nova Scotia, Canada. Further, we tested the relationship between migratory behaviour and survival and used mark-recapture models to examine the role of body length and tag-to-body mass as survival covariates. Survival was most heavily impacted in estuarine habitats closest to head-of-tide. Survival was affected by body length at three of four sites. The shape and spatial variability of the body lengthsurvival relationship provided insight on mortality vectors, highlighting the potential roles of predation and osmotic stress. Survival was not influenced by repeated landward-seaward migratory movements; however, there was a significant correlation between residency and survival.Résumé : La télémétrie acoustique est un outil utile pour la surveillance de la survie et du comportement en estuaire des post-saumoneaux de saumon atlantique. Dans la plupart des cas, le taux de survie signalé est la fraction statique de postsaumoneaux marqués détectés et, si le moment et le lieu de la mortalité peuvent être mentionnés, les covariables du taux de survie ou de la relation entre le comportement migratoire et la survie sont moins souvent rapportées. Dans cette l'étude, nous avons fait appel à la télémétrie acoustique pour suivre des saumoneaux de saumon atlantique en migration de la mer vers quatre rivières de la Nouvelle-Écosse (Canada). Nous avons en outre vérifié le lien entre le comportement migratoire et le taux de survie et utilisé des modèles de marquage-recapture pour examiner la longueur du corps et le rapport entre le poids de la marque et celui du corps comme covariables éventuelles du taux de survie. Les impacts sur ce dernier étaient les plus forts dans les habitats estuariens situés les plus près de la limite de marée. Dans quatre sites, la longueur du corps avait une incidence sur le taux de survie. La forme et la variabilité spatiale de la relation entre la longueur du corps et le taux de survie ont mis en lumière des vecteurs de mortalité, faisant ressortir un rôle possible de la prédation et du stress osmotique. Si les déplacements migratoires répétés vers la terre ou vers la mer n'avaient pas d'incidence sur le taux de survie, une corrélation significative a cependant été notée entre le temps de résidence et le taux de survie. [Traduit par la Rédaction]