Abstract
AbstractAcoustic 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 angleSD: 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 (walleyeSander vitreus, common carpCyprinus carpioand channel catfishIctalurus 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.
Highlights
Acoustic telemetry has gained widespread popularity as a tool to understand migration, habitat use and survival of aquatic animals (Cooke et al, 2013; Hussey et al, 2015)
Our interest in developing a simulation was inspired by current research in Lake Erie on the migration of walleye Sander vitreus, in which a double receiver-line was initially used with overlapping detection ranges and took advantage of geographic bottlenecks between islands that naturally partitioned spawning areas from seasonal feeding habitats (Raby et al, 2018)
A quantitative description of individual aquatic animal movements has long been an active area of research, and random walk models have frequently provided either useful descriptions or valuable null models (Gurarie et al, 2016; Turchin, 1998)
Summary
Acoustic telemetry has gained widespread popularity as a tool to understand migration, habitat use and survival of aquatic animals (Cooke et al, 2013; Hussey et al, 2015). Just how much novel information can be obtained in an acoustic telemetry study pivots on the spatial arrangement of receivers, which are commonly moored at fixed locations to passively monitor tagged individuals. We had enough receivers (n = 72) to redistribute into a 15-km grid across the central basin of the lake, but we had scant information on whether this change would still achieve our objective of timing fish passage around the islands and reduce redundancy in our data. We evaluated this question through a simulation
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