Case report: comparison of NexTrak and VR2 acoustic receiver performance in a low-noise coastal marine environment

Acoustic telemetry is a common methodology in the study of animal movement, behaviour, and physiology in aquatic environments. In the marine environment, receiver performance is limited by environmental conditions and habitat (which modulate receiver detection range) and the number of tagged animals in the system (with signal collisions reducing the receiver’s ability to decode unique transmitter IDs). The Innovasea NexTrak receiver was developed to address the key challenges of detection range, number of transmissions successfully decoded, and quality of detection data. To assess how NexTrak receivers perform relative to the commonly used VR2AR receiver, we co-deployed NexTrak and VR2AR receivers on six moorings within a larger acoustic array deployed to study white shark movement ecology in Mahone Bay, Nova Scotia, Canada. We compared receiver performance in terms of (i) number of animals detected, (ii) number of transmissions received, (iii) structure and duration of detection events, and (iv) the effects of environmental noise on detection rates. Results showed 27.7 ± 14.4% more white sharks and 86.0 ± 20.9% more detections for NexTrak relative to VR2AR. At the detection-event level, NexTrak recorded more detections (3.9 ± 3.6, range: 0–19) than VR2AR (2.2 ± 3.0, range: 0–11). Detection events were also longer for NexTrak (471 ± 321 s, range: 0–1549 s) than for VR2AR (324 ± 241 s, range: 0–893 s), equating to a 45% higher detection-event duration as a proxy for increased detection range. While noise was a significant predictor of hourly detections, with each mV increase associated with a ~ 0.4% reduction in detections, there was no discernable difference between NexTrak and VR2AR in their performance relative to noise in our relatively quiet study system. Overall, it is evident that the NexTrak receiver has the potential to improve acoustic telemetry capabilities though enhanced detection efficiency and data quality relative to VR2AR. Improvements in detection range and decoding efficiency have implications for research costs, array design decisions, and the accuracy and precision of continuous movement tracks in fine-scale positioning arrays.