A programmable acoustic recording tag and first results from free-ranging northern elephant seals

A hydrophone-equipped tag recorded exposure to noise, as well as physiologi cal and behavioral sounds, on free-ranging northern elephant seals (Miroung a angustirostris). The compact acoustic probe (CAP) consisted of the hydrop hone, a thermistor, and a pressure transducer in a 36 cm long, 10 cm diamet er cylindrical hydrodynamic housing capable of withstanding 2000 m depth. T he enclosed logging electronics included a programmable "TattleTale 7" data acquisition engine and a 340 Mb hard disk. A custom low-power operating sy stem supported multi-channel interrupt-driven sampling at 5 kHz. The comple te tag weighed 0.9 kg in water and displaced 2.1 l. During five deployments on juveniles translocated from and returning to Ano Nuevo, California, CAP tags measured dive pattern, ambient and vessel noise exposure, oceanograph ic ranging (RAFOS) and thermometry (ATOC) beacons, acoustic signatures of s wim stroke, surface respiration, and cardiac function, and possible vocaliz ations. (C) 1998 Elsevier Science Ltd. All rights reserved.