Does the telemetry technology matter? Comparing estimates of aquatic animal space-use generated from GPS-based and passive acoustic tracking

Abstract

Underwater passive acoustic (PA) telemetry is becoming the preferred technology for investigating animal movement in aquatic systems; however, much of the current statistical tools for telemetry data were established from global positioning system (GPS)-based data. To understand the appropriateness of these tools for PA telemetry, we dual-tagged free-ranging aquatic animals that exist at the air-water interface (Crocodylus porosus, n=14). The location of each animal was simultaneously recorded over a 3-month period by fixed acoustic receivers and satellite positioning. Estimates of minimum travel distance and home range (HR) were then calculated from the PA and GPS datasets. The study revealed significant disparity between telemetry technologies in estimates of minimum travel distance and HR size. Of the five HR measures investigated, the linear distance measure produced the most comparable estimates of HR size and overlap. The kernel utilisation distribution with a reference smoothing parameter function and ad hoc function, however, produced comparable estimates when raw acoustic detections were grouped into periods when animals were within and between receiver detection fields. The study offers guidelines on how to improve the accuracy and precision of space-use estimates from PA telemetry, even in receiver arrangements with large areas of non-detection.

Feeding across the food web: The interaction between diet, movement and body size in estuarine crocodiles (Crocodylus porosus)

“…As crocodiles remained within the main trunk of the river during the study period, we treated the study area as a one‐dimensional space: distance along the Wenlock River from its river mouth. The location of each receiver was expressed as the shortest distance along the river to its coordinates from the river mouth (similar to ‘linear distance’ methods by Dwyer et al . in press).…”

“…To represent frequency of usage along the river, we used the duration of time that an individual remained near each receiver station, rather than raw detections (Campbell et al . ; Dwyer et al . in press).…”

Evaluating GPS biologging technology for studying spatial ecology of large constricting snakes

“…To study reptiles, GPS biotelemetry (as opposed to satellite tracking, e.g., the ARGOS system, for definitions see [3]) has been used only sparingly, primarily on marine turtles [e.g., 12] and crocodilians [e.g., [13][14][15]. Among squamates, only large lizards such as blue-tongue skinks and monitor lizards have been tracked using GPS tags [e.g., 16,17].…”

A standardised framework for analysing animal detections from automated tracking arrays

“…Smoothing factors significantly influence calculated estimates of activity space metrics using kernel methods [Fig. 5;23,27]. The fixed KUD method requires a single smoothing parameter (δ 2 ) related to imprecision of relocation.…”

“…In each case, different analytical approaches that account for spatiotemporal autocorrelation (e.g. estimation of short-term centres of activity, randomisation within receiver range) in subtly different ways and a variety of smoothing factors were used, making direct comparisons unreliable because KUD estimations are sensitive to the chosen smoothing factor [23]. Application of a single tool-set with defined parameters could produce directly comparable results for each of these species.…”