A new acoustic tailbeat transmitter for ®shes

A new acoustic transmitter for monitoring the tailbeat frequency of free-swimming ®shes and sharks is described. The transmitter is externally mounted on the ®sh'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 de ̄ections from free-swimming sharks. Tests in a ̄ume 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 ®shes and sharks in the ®eld. # 1998 Elsevier Science B.V. All rights reserved.