A new acoustic tailbeat transmitter for fishes

A new acoustic transmitter for monitoring the tailbeat frequency of free-swimming fishes and sharks is described. The transmitter is externally mounted on the fish's caudal peduncle and produces an acoustic pulse with every lateral movement of the tail. Field tests on obligate-swimming juvenile scalloped hammerhead sharks (Sphyrna lewini) show these transmitters accurately telemeter tailbeat deflections from free-swimming sharks. Tests in a flume show sharks with transmitters work harder and swim slower than sharks without transmitters, but these laboratory data can be used to correct for instrument artifacts on free-swimming sharks. A shark tracked with a tailbeat-sensing transmitter exhibited similar movement and activity patterns to shark pups tracked with smaller, orally inserted internal transmitters. The similarity of tracks indicate that the shark equipped with the tailbeat transmitter behaved normally. Thus, this new transmitter design offers a cost-effective, minimally intrusive method for accurately measuring activity rate and energy consumption of active fishes and sharks in the field.