Does transmitter placement or species affect detection efficiency of tagged animals in biotelemetry research?

Acoustic telemetry has quickly become a powerful tool for ecological research in aquatic systems, yet our knowledge of in situ transmitter performance remains limited. Here, we used an experimental approach to test the influence of three biotic factors on the detection range of acoustic transmitters: (1) internal versus external placement of the transmitter on a model finfish species, red drum (Sciaenops ocellatus); (2) attachment of a transmitter on an animal host (red drum) versus a fixed object; and (3) species comparison between internally tagged red drum and southern flounder (Paralichthys lethostigma). Significant differences in detection probability were observed between internally and externally placed transmitters as well as between transmitters attached to an animal host (red drum) and those attached to a fixed line, while no effect was observed between the two species tested. External transmitters were detected significantly more than corresponding internal transmitters in red drum, and outperformed internal transmitters by 2-7 fold at distances >100m. Similarly, detection probability declined more quickly as a function of distance for transmitters attached to red drum relative to transmitters attached to a fixed line, with greater differences observed at distances >300m. Findings from this study challenge commonly held assumptions in acoustic telemetry research and suggest that traditional range testing methods are likely to considerably overestimate detection range of tagged animals in situ. Accounting for the influence of transmitter placement will enhance study design in acoustic telemetry research and ultimately improve detection efficiency and data interpretation in animal movement studies.