Evaluation of three telemetry transmitter attachment methods for female silver-phase American eels ( Anguilla rostrata Lesueur)

Declines in juvenile American eel (Anguilla rostrata Lesueur) abundance have led to concern about the impacts of anthropogenic structures on eel migration patterns. Telemetry provides an insightful tool for examining the movements of eels around these structures. Although there have been a number of studies investigating movements of Anguillid eels, using a variety of transmitter attachment techniques, there are few published evaluations of the effects of various tag attachment procedures. Hence, the effects of three telemetry attachment procedures were evaluated for female silver phase American eels. Short-term effects were examined by comparing the swimming performance of control eels and surgical shams with the swimming capacity of eels tagged externally, internally, and gastrically 24-hours following surgeries. Adaptive effects were investigated using a second swim trial 8 to 10 weeks following surgical procedures. Additionally, 12-week transmitter retention rates were calculated for each attachment method. Critical swimming velocity was not significantly different between treatments (P > 0.05), but did decrease significantly between trials (P = 0.012), suggesting that the swimming capacity of silver-phase American eels is not affected by the presence of telemetry transmitters or the method of transmitter attachment, even though swim performance decreases. However, transmitter retention rates varied considerably after the 12-week experimental period. Three gastric tags were regurgitated for a 12-week retention rate of 72.7%. No surgically implanted transmitters were shed, while 11 out of 12 externally affixed transmitters were lost, resulting in a retention rate of only 9.1%. These results suggest that surgically implanting transmitters is the preferred method of affixing telemetry transmitters to American eels especially for long-term telemetry studies.