Evaluation of acoustic telemetry grids for determining aquatic animal movement and survival

Abstract

Acoustic telemetry studies have frequently prioritized linear configurations of hydrophone receivers, such as perpendicular from shorelines or across rivers, to detect the presence of tagged aquatic animals. This approach introduces unknown bias when receivers are stationed for convenience at geographic bottlenecks (e.g. at the mouth of an embayment or between islands) as opposed to deployments following a statistical sampling design. We evaluated two‐dimensional acoustic receiver arrays (grids: receivers spread uniformly across space) as an alternative approach to provide estimates of survival, movement and habitat use. Performance of variably spaced receiver grids (5–25 km spacing) was evaluated by simulating (1) animal tracks as correlated random walks (speed: 0.1–0.9 m/s; turning angle SD: 5–30°); (2) variable tag transmission intervals along each track (nominal delay: 15–300 s); and (3) probability of detection of each transmission based on logistic detection range curves (mid‐point: 200–1,500 m). From simulations, we quantified (i) time between successive detections on any receiver (detection time), (ii) time between successive detections on different receivers (transit time), and (iii) distance between successive detections on different receivers (transit distance). In the most restrictive detection range scenario (200 m), the 95th percentile of transit time was 3.2 days at 5 km, 5.7 days at 7 km and 15.2 days at 25 km grid spacing; for the 1,500 m detection range scenario, it was 0.1 days at 5 km, 0.5 days at 7 km and 10.8 days at 25 km. These values represented upper bounds on the expected maximum time that an animal could go undetected. Comparison of the simulations with pilot studies on three fishes (walleye Sander vitreus, common carp Cyprinus carpio and channel catfish Ictalurus punctatus) from two independent large lake ecosystems (lakes Erie and Winnipeg) revealed shorter detection and transit times than what simulations predicted. By spreading effort uniformly across space, grids can improve understanding of fish migration over the commonly employed receiver line approach, but at increased time cost for maintaining grids.

Vertical Habitat Use by Adult Walleyes Conflicts with Expectations from Fishery‐Independent Surveys

“…; Kraus et al. ), which is much greater than the depth of the lake at our receiver locations and unlikely to account for a lack of shallow detections. Additionally, a strong density gradient due to a thermocline can reflect sound transmitted by telemetry tags (Kessel et al.…”

Influence of thermal stratification and storms on acoustic telemetry detection efficiency: a year-long test in the US Southern Mid-Atlantic Bight

“…The detection probability of ultrasonic transmitters utilized in acoustic biotelemetry, hereafter referred to as detectability, varies with seasonal and event-scale physical changes in the environment [2]; still, many studies do not address temporal changes in detection probability and assume a constant value or apply previously-calculated values to different types of environments [1,3]. In gated and gridded designs of receivers, changes in detection probability can alternatively occlude or exaggerate assessed presence of telemetered animals if detection ranges are not adequately known [4]. Indeed, there has been an increase in studies incorporating long-term range testing to either directly scale results [5] or to inform detection range due to local features [6,7].…”

Acoustic telemetry as a potential tool for mixed-stock analysis of fishery harvest: a feasibility study using Lake Erie walleye

“…Use of acoustic telemetry to estimate survival may suffer from some level of bias if detection probabilities are reduced for extended periods of time or if tagged individuals do not encounter an acoustic receiver. However, acoustic receivers deployed in a grid across a given study area (versus deployed in a gate with limited spatial coverage), such as done here, provide improved spatial and temporal information about a tagged individual's fate across a range of conditions (e.g., detection probability, tag power; see Kraus et al 2018). Potential false-positive detections due to code collision (Beeman and Perry 2012) were removed from the data using Pincock's (2012) criteria, resulting in a database of 178 358 detections comprising individual detection histories.…”