Evaluation of a flipper-mounted transmitter on sea otters

Small radiotransmitters, powered by lithium batteries or solar cells and epoxied to cattle ear tags, were attached to the interdigital webbing of a hind foot on 75 California sea otters (Enhydra lutris nereis). Observations of 54 otters that stayed in the California coastal study area beyond expected battery life (60 days) indicated that tags with radios were retained for ≤263 days on average. Radiotags damaged flipper webbing in 34% of 53 otters observed after tags were attached. This tag design is easily applied when short-term monitoring is needed and offers a functional alternative when intraperitoneal-implanted transmitters are not advised.