Abstract:
A self-contained acoustic recording tag has obtained signatures of heartbeat from both captive and free-ranging northern elephant seals (Mirounga angustirostris). Simultaneous electrocardiogram (ECG) and acoustic signatures obtained from the submerged captive seal confirm that seal heartbeat can be monitored acoustically. Recordings from the free-ranging seal demonstrate shallow-water apneic heart rates of 40 to 55 beats per minute, comparable to past observations with ECG tags. Observation of a sixfold increase in beat amplitude at the surface (110 dB re: 1 (mu)Pa) over that at depth (94 dB re: 1 (mu)Pa) may reflect increases in stroke volume at the surface. The findings suggest the feasibility of long-term, reliable, quantitative, and noninvasive cardiac monitoring of a variety of free-ranging marine animals using acoustic logging techniques. [Work supported by MBARI and ONR.]