Retention and effects of miniature transmitters in juvenile American eels

Abstract

The purpose of this study was to assess the effects of an acoustic micro transmitter (tag) on survival and swimming ability of juvenile American eels (Anguilla rostrata). The transmitter was designed for implantation through a<3mm opening into the body cavity of anguilliform fishes without the need for sutures. Potential transmitter effects on swimming performance were examined by comparing critical swimming speeds (Ucrit, an index of prolonged swimming performance) for six size groups (n=120, 113–175 mm) of tagged and non-tagged eels. There was no significant difference in Ucrits between tagged and non-tagged eels. Median Ucrits for tagged eels ranged from 50.2cm/s for the smallest group tested (113–119mm) to 63.9cm/s for eels 141–150mm in length. Non-tagged group median Ucrits ranged from 47.2cm/s for the smallest group to 66.9cm/s for the 141–150mm group. An additional 26 eels (115–208mm) were tagged and held for 38days (without undergoing swimming performance tests) to assess survival and tag loss. No mortality occurred during the holding period and a tag loss of 3.8% (n=1) was observed within the first 20days post-tagging, which is the current projected battery life of the tag at a 5s ping rate interval. Tag loss increased to 50% overall (n=13) for eels held up to 38days. Our results indicate that micro acoustic tags can be successfully implanted in juvenile American eels with no apparent effects on swimming ability or survival, and would be a viable option for examining eel movement patterns in river systems and near hydroelectric facilities.