Detection Range of Acoustic Transmitters in an Estuarine Environment: Does Attachment Method or Species Affect Performance?

Acoustic telemetry has quickly become a powerful tool in fisheries ecology, yet our knowledge of in situ transmitter performance is limited. An experimental approach was used to test three effects on detection range in an estuarine environment: 1) body wall (internal vs. external tagging), 2) transmitter placement (fixed vs. externally on fish), and 3) differences in body morphology for internally tagged fish (Red Drum vs. Southern Flounder).  Each paired comparison (internal/external, external/fixed, species) consisted of 3-5 replicate trials conducted on separate days. Fish were fitted with an internal and/or external transmitter (Vemco V9-1H, 69kHz) and placed inside a 1 m³ mesh enclosure at the origin of a line of receivers deployed at known distances from the enclosure (0, 50, 100, 150, 200, 250, 300, 400, 500, and 600m). Significant differences in detection probability were observed between internally and externally attached transmitters as well as between fixed and external transmitters, while no species effect was observed. External transmitters significantly outperformed internal transmitters at distances > 100m, while fixed transmitters outperformed external transmitters at distances > 300m. Results suggest that transmitter attachment method affects detection range, and should be considered in study design and interpretation of data for future acoustic telemetry studies.