Transintestinal expulsion of surgically implanted dummy transmitters by bluefin trevally: Implications for long-term movement studies

The feasibility of long-term acoustic monitoring of coral reef fish movements was evaluated by quantifying transmitter retention times for captive bluefin trevally Caranx melampygus and detection patterns of transmitter-implanted free-ranging bluefin trevally. Wax-coated dummy transmitters (9 X 22 mm; 3.6 g) were surgically implanted into the gut cavity of four captive bluefin trevally. The fish retained the dummy transmitters for 17-22 months, but at the end of the study transintestinal expulsion was in progress in one individual. Five bluefin trevally captured at Honokohau, Hawaii, were surgically implanted with long-life (1-year) coded transmitters and released. Their movements were monitored with the use of 27 underwater receivers deployed along a 115-km stretch of coastline. The five bluefin trevally were detected by the receivers over periods ranging from I to 173 d (mean, 60 d), and their movements spanned up to 10.2 km of coastline. Daily movements were consistent with those observed by previous short-term active tracking studies and consisted of crepuscular migrations of 1-2 km between separate daytime and nighttime habitats. These data suggest that passive monitoring of bluefin trevally movements for periods of up to 22 months is theoretically possible and that transmitter expulsion is not necessarily the cause of shorter detection periods.