Kennedy, R. J., Evans, D., Allen, M. 2020. Long-term retention of dummy acoustic transmitters in adult brown trout. Journal of Fish Biology 97(4), 1281–1284.

A group of 36 1+ age class Salmo trutta were surgically implanted with dummy acoustic tags and monitored for 370 days. In total 13 tags were expelled throughout the experiment with an overall tag loss rate of c. 0.035 tags per day. Fish length was the only explanatory variable which had a significant association with subsequent tag expulsion. The estimated probability of retaining a tag for a year for a fish of length32 cm was 0.76, 34 cm was 0.60 and 36 cm was 0.38. The long-term tag loss patterns were examined and discussed. “The potential for an initial high tag retention period, followed by a short phase of increased losses and a final longer, more stable shedding rate, may, if replicated in wild fish and other species, represent an important consideration in the interpretation of long‐term telemetry data. By being able to see the unseen, the use of ultrasound as an alternative method to traditionally used invasive methods reduced handling stress (improving animal welfare) and eliminated the need for periodic dissections. Like other researchers, we advocate that ultrasound imaging offers great opportunities as a tool for ecological studies in wild fish. The work clearly demonstrates the pressing need to perform additional, longer‐term research on the retention of transmitters across different life stages, size ranges and growth conditions with which to complement and inform the increasing body of telemetry research on fish.”

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