Acoustic telemetry detection probability and location accuracy in a freshwater wetland embayment

Abstract

Background In recent years, large-scale acoustic telemetry observation networks have become established globally to gain a better understanding of the ecology, movements and population dynamics of fish stocks. When studying a species that uses different habitats throughout its life history difficulty may arise where acoustically suboptimal habitats are used, such as shallow, vegetated areas. To test the feasibility of active tracking in these acoustically suboptimal habitats, we quantified detection probability and location error as a function of several environmental variables with two transmitter types in a shallow freshwater embayment. Results When placed in nearshore areas (< 1 m deep), the higher-powered transmitter (158 dB) had significantly greater detection probability than the lower-powered transmitter (152 dB). For both transmitter types, detection probability declined at 200 m; however, at the 100 m distance the higher-powered transmitter had greater than 50% detection probability per ping cycle (50.4%) while the lower-powered transmitter was substantially less (29.4%). Additionally, detection probability increased when the transmitter was deployed within sparse, senescent Phragmites spp. vegetation (14%). Estimated positional accuracy of transmitters deployed at known locations (location error) was variable (error range: 13–259 m), and was generally higher for the more powerful transmitter. Location error was minimized when the lower-powered transmitter was located near softened shoreline areas compared to near man-made armored shorelines (i.e., rip-rap). Conclusion While benefits exist for maximizing transmitter power (e.g., increased detection range in open-water environments), use of a lower-powered transmitter may be advantageous for active tracking specific locations of fish inhabiting shallow water environments, such as in estuarine tidal marshes and shallow wetlands. Thus, when planning acoustic telemetry studies, researchers should conduct site-specific preliminary detection probability/location error experiments to better understand the utility of acoustic telemetry to investigate fish movements in acoustically suboptimal conditions.

Influence of dense macrophyte vegetation and total gas saturation on the performance of acoustic telemetry

“…The significant effect of day-of-year is thus related to temperature rather than macrophyte growth or senescence. A single study, from a shallow (< 1 m) freshwater wetland, found a positive effect of macrophyte presence on detection probability, but this was explained as an artefact of the nested nature of the random effects that could not be accounted for in the study design [26]. The impact of Here positional accuracy and precision were significantly lower when transmitters were positioned within seagrass (0.9 m) compared to above (0.45 m) [27].…”

“…Performance of acoustic telemetry is poorly understood in shallow freshwater ecosystems with dense aquatic macrophytes [26,27,31]. Macrophytes are structurally complex and often considered as ecosystem engineers in freshwater ecosystems due to their key functions for ecosystem structure and functions [12].…”

“…Macrophytes are likely to obstruct the signal by causing a physical barrier for sound propagation together with their photosynthetic activity producing oxygen emitted as air bubbles that influence on sound propagation [5,33]. Recently, some studies have evaluated the performance of acoustic telemetry in ecosystems with aquatic macrophytes [26,27,31], but no studies have yet performed in situ range testing and evaluated positioning systems in shallow ecosystems with very dense macrophytes growth, i.e., mass developments. Successful implementation of acoustic telemetry in ecosystems with high densities of macrophytes will require understanding of how macrophytes influence detection efficiency and detection range to determine the restrictions that may constrain the conclusions in such studies.…”

Taking the time for range testing: an approach to account for temporal resolution in acoustic telemetry detection range assessments

“…When investigating the sequence of detections in space, range can be assessed specifically for migratory routes [50] or network analysis [38]. For fine-scale positioning, horizontal position errors would be quantified within an entire receiver array [8], potentially accounting for individual receiver's contributions [51] and system settings [52].…”

“…Environmental impacts include static features, such as habitat type and bottom depth [2,3], as well as system dynamics that vary over time, such as wind, water currents, precipitation, biogenic and anthropogenic noise, temperature and stratification [4][5][6]. The detection range can also be dependent on the specifications of the equipment used, including transmitter type, transmitting power output and transmitter placement [7][8][9], as well as receiver depth, orientation and deployment method [5,10,11]. Biofouling on the receiver can significantly decrease receiver performance over time [12].…”