Abstract
BackgroundAcoustic telemetry is a commonly used tool to gain knowledge about aquatic animal ecology through the study of their movements. In telemetry studies researchers must make inferences regarding the movements and the fates of tagged animals. Until recently, predation has been inferred in telemetry data using a variety of methods including abrupt changes in movement patterns or habitat use. An acoustic telemetry transmitter has been developed to detect predation events of tagged animals, and while they have performed well in controlled laboratory trials, literature regarding the application of these novel transmitters in field settings is limited. The objective of this research was to describe the detection data obtained from field studies using predation tags and propose methods to incorporate this information in decision-making about the fate of tagged animals. We implanted 60 yellow perch (Perca flavescens) with predation transmitters and evaluated their spatial use in a receiver array (34 ha) using a combination of centres of activity, roaming indices, and step length measures to examine detection data.ResultsOver 5 months, 19 apparent predation events were identified by the transmitters. Roaming indices and centres of activity revealed a variety of detection patterns, including instances of altered behaviour before and after predation that matched tag-indentified predation events, dropped tags post-predation, and detections that ceased post-predation indicating the predator might have left the array. Based on the observed patterns, probable predation was inferred for 15 of 19 triggered tags, with unclear fates for four fish.ConclusionsOur study provided a framework to assess the fate of animals tagged with predation transmitters and demonstrate how these tags can contribute to telemetry studies. We showed how detections can be categorized using tag status to compare movement metrics among individuals, provided tools to explore space use surrounding predation events, and synthesized this information to inform uncertainty surrounding tag-identified predation events. Predation tags do not remove all uncertainty about the fate of tagged individuals, but combined with other metrics they increase the likelihood of identifying abnormal movements that could otherwise introduce biased detection histories into studies of small-sized fishes.
Highlights
Acoustic telemetry is a commonly used tool to gain knowledge about aquatic animal ecology through the study of their movements
Predation stage classification For this study, we focused on tags that indicated a predation event, in part because the focus of this paper was to describe the detection data gathered from predation tags to infer the fate of individuals more so than to consider ecological questions about predated and non-predated yellow perch
As predation tags are a new technology, at this time we argue that rather than using the tags as the only indicator of predation, examining each individual using multiple metrics of habitat use combined with predation tags allowed for informed decision-making about the fates of tagged fish while acknowledging uncertainty surrounding predation events
Summary
Acoustic telemetry is a commonly used tool to gain knowledge about aquatic animal ecology through the study of their movements. Sudden changes in temperature have been used to identify the predation of American eels (Anguilla rostrata) by endothermic predators, and further investigation of depthprofile data of the two potential warm-gutted predators in the area led to the identification of the likely predator [3] This approach requires the use of transmitters with additional temperature or depth sensors which are not often available for smaller tags used to track small animals. The survival of Atlantic salmon smolts (Salmo salar) has been inferred by comparing movement paths of tagged salmon smolts to those of tagged Striped bass (Morone saxatilis) and using behavioural classification to identify probable predation events [2] This method relies on predators and prey exhibiting discrete movement patterns and having detection data for all potential predators, limiting the broadscale utility of this method to infer predation. As such, inferring predation events based solely on animal movements is challenging but this information can provide critical knowledge about ecological relationships to advise conservation and management programmes
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