Evaluation of an acoustic telemetry transmitter designed to identify predation events

Abstract

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.

Estimating consumption rate of Atlantic salmon smolts (Salmo salar) by striped bass (Morone saxatilis) in the Miramichi River estuary using acoustic telemetry

“…One such technology is predator tags which can signal consumption 386 events based on a change in identification code triggered by the change in pH associated with the 387 predator's gastrointestinal tract (Halfyard et al 2017). This technology could define predation events 388 more precisely than from movement pattern data as used in this study.…”

Understanding and managing fish populations: keeping the toolbox fit for purpose

“…Acoustic telemetry offers autonomous, continuous monitoring (Heupel et al, ) and has the potential to significantly enhance our understanding of fish habitat use, activity patterns and resource partitioning (Hussey et al, ). Acoustic arrays have been used in many studies elucidating fish movements (Papastamatiou et al, ; Lea et al, ) and transmitters have been used more innovatively to measure trophic interactions (Halfyard et al, ). Issues remain however, in the significant cost and effort involved in deploying and maintaining acoustic arrays.…”

Survival and migration patterns of naturally and hatchery‐reared Atlantic salmon (Salmo salar) smolts in a Lake Ontario tributary using acoustic telemetry

“…Two types of tags were used throughout the study: V5s (Vemco V5‐2H 180 kHz; length: 13 mm; mass in air: 0.65 g; estimated battery life: 128–140 days; nominal delay: 40–80 s) and predation tags (Vemco V5D‐1H 180 kHz; length: 13 mm; mass in air: 0.68 g; estimated battery life: 108 days; nominal delay: 40–80 s) which trigger a new identification code upon being consumed (Halfyard et al, ). In 2017, all tagged fish had V5 tags ( n = 40), while in 2018 fish were tagged with either a V5 or predation tag ( n = 15 for each tag type, for both hatchery‐ and naturally reared fish).…”