Performance Assessment of Two Whole-Lake Acoustic Positional Telemetry Systems - Is Reality Mining of Free-Ranging Aquatic Animals Technologically Possible?

Abstract

Acoustic positional telemetry systems (APTs) represent a novel approach to study the behaviour of free ranging aquatic animals in the wild at unprecedented detail. System manufactures promise remarkably high temporal and spatial resolution. However, the performance of APTs has rarely been rigorously tested at the level of entire ecosystems. Moreover, the effect of habitat structure on system performance has only been poorly documented. Two APTs were deployed to cover two small lakes and a series of standardized stationary tests were conducted to assess system performance. Furthermore, a number of tow tests were conducted to simulate moving fish. Based on these data, we quantified system performance in terms of data yield, accuracy and precision as a function of structural complexity in relation to vegetation. Mean data yield of the two systems was 40 % (Lake1) and 60 % (Lake2). Average system accuracy (acc) and precision (prec) were Lake1: acc = 3.1 m, prec = 1.1 m; Lake2: acc = 1.0 m, prec = 0.2 m. System performance was negatively affected by structural complexity, i.e., open water habitats yielded far better performance than structurally complex vegetated habitats. Post-processing greatly improved data quality, and sub-meter accuracy and precision were, on average, regularly achieved in Lake2 but remained the exception in the larger and structurally more complex Lake1. Moving transmitters were tracked well by both systems. Whereas overestimation of moved distance is inevitable for stationary transmitters due to accumulation of small tracking errors, moving transmitters can result in both over- and underestimation of distances depending on circumstances. Both deployed APTs were capable of providing high resolution positional data at the scale of entire lakes and are suitable systems to mine the reality of free ranging fish in their natural environment. This opens important opportunities to advance several fields of study such as movement ecology and animal social networks in the wild. It is recommended that thorough performance tests are conducted in any study utilizing APTs. The APTs tested here appear best suited for studies in structurally simple ecosystems or for studying pelagic species. In such situations, the data quality provided by the APTs is exceptionally high.

A method of spatial correction for acoustic positioning biotelemetry

“…Signals in an aquatic environment are analogous to signals travelling down a canyon, where the canyon walls can reflect signals, but in the case of a freshwater or marine system one of the "walls" (the surface of the water) is a dynamic interface affected by wind and other environmental factors [24]. Similar results were obtained by Baktoft et al [25], where the authors tested an acoustic telemetry system on two lakes. The depth trials suggest that space use of tagged animals that inhabit the upper water column may be considerably overestimated compared to those living deeper in the water column.…”

“…1) over a period of approximately 24 h. The panels show: a raw telemetry data; b a SSM was applied to correct for measurement errors; c a correction for systematic bias (determined by kriging); d systematic (kriging) and measurement errors (SSM) were accounted for study when transmitters were located far from the centre of the triads. In our study, a normal distribution was used to describe the error structure of the detections in the SSM, but [25] used a hidden Markov model (HMM) and a t-distribution to model measurement errors (the authors refer to them as observation errors). Although this technique did not address any systematic biases that may have been present, this approach did improve the data (with some residual scattering around the true positions).…”

Between- and within-individual variation in activity increases with water temperature in wild perch

“…The average data yield (i.e., the percentage of transmissions yielding a valid position) of the wholelake telemetry system was 40%, and the accuracy was 3.1 m for horizontal position and 0.3 m for vertical position. Further details of the system can be found in Baktoft et al (2015).…”

Spatial and temporal variation in positioning probability of acoustic telemetry arrays: fine-scale variability and complex interactions

“…While spatial variation in positioning probability has been noted in other studies [15,16], most studies have focused on receiver geometry and ignored temporal variability [16][17][18]. This trend may be due to the fact that most assessment studies were short in duration [1,15,17], or used positional arrays with relatively small spatial coverage [1,11,15,18]. The long duration, high environmental complexity, and large spatial extent of our VPS deployment provided a unique opportunity to explore and quantify within-array variability in positioning probability.…”

“…Studies describing variation in detection probability of presence/absence telemetry systems are abundant (reviewed in [12,14]), but perhaps due to the relative novelty of positional telemetry and also possibly a disconnect between the end user (researcher) and the position estimation process, few papers have assessed spatial and temporal performance variability of positional telemetry systems [11,[15][16][17][18]. The primary focus of most positional telemetry performance studies has been position accuracy.…”