Efficacy of an Acoustic Tag with Predation Detection Technology

One of the most important assumptions in the use of data from an acoustically tagged fish is that the data are indeed from the fish that was originally tagged. However, there is likely to be some level of predation on the tagged subjects used in acoustic telemetry studies. When an acoustically tagged fish is consumed, the tag continues to emit the same signal even though the tagged fish is no longer alive. To assist in addressing this issue, a predation detection acoustic tag (PDAT) was developed to provide the functions of a typical acoustic tag with the added ability to indicate when a tagged fish has been consumed by a predator. Our goal was to test the efficacy and precision of this new technology. We implanted PDATs into live juvenile Chinook Salmon Oncorhynchus tshawytscha and fed them to adult Striped Bass Morone saxatilis under controlled conditions. Identifying when the PDATs "triggered" (i.e., changed their signal, indicating that the tag had been consumed) proved to be a simple process. The PDAT that we tested was effective 90% of the time in verifying that a tagged fish had been consumed. The mean elapsed time from the feeding event to the time of triggering (trigger time) was 59.2 h (SD = 28.1, range = 22.3-140.0). The PDAT has great potential to assist in more accurately interpreting acoustic data in the study of fish behavior and survival. Further testing of this technology is warranted and should include a broader range of the environmental factors likely to have a major influence on trigger time as well as trials under more natural conditions.