Retention and effects of miniature transmitters in juvenile American eels

- Transmitter effects for a micro (0.088 g) acoustic transmitter were evaluated in juvenile American eel.
- Swimming performance and tag loss were evaluated in yellow stage American eel (113-175 mm).
- Swimming performance was not impaired for any size groups implanted with a transmitter.
- Tag loss was observed and occurred from day 14 to the end of the holding period (38 days).

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 < 3 mm 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 50.2 cm/s for the smallest group tested (113-119 mm) to 63.9 cm/s for eels 141-150 mm in length. Non-tagged group median Ucrits ranged from 47.2 cm/s for the smallest group to 66.9 cm/s for the 141-150 mm group. An additional 26 eels (115-208 mm) were tagged and held for 38 days (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 20 days post-tagging, which is the current projected battery life of the tag at a 5 s ping rate interval. Tag loss increased to 50% overall (n = 13) for eels held up to 38 days. 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.