The production of venous gas emboli (VGE) resulting from altered dive behavior is postulated as contributing to the stranding of beaked whales exposed to mid-frequency active sonar. To test whether nitrogen gas uptake during repetitive breath-hold diving is sufficient for asymptomatic VGE formation in odontocetes, a bottlenose dolphin (Tursiops truncatus Montagu) was trained to perform 10–12 serial dives with 60s surface intervals to depths of 30, 50, 70 or 100m. The dolphin remained at the bottom depth for 90s on each dive. Doppler and/or two-dimensional imaging ultrasound did not detect VGE in the portal and brachiocephalic veins following a dive series. Van Slyke analyses of serial, post-dive blood samples drawn from the fluke yielded blood nitrogen partial pressure (PN2) values that were negligibly different from control samples. Mean heart rate (HR; ±1s.d.) recorded during diving was 50±3 beats min–1 and was not significantly different between the 50, 70 and 100m dive sessions. The absence of VGE and elevated blood PN2 during post-dive periods do not support the hypothesis that N2 supersaturation during repetitive dives contributes to VGE formation in the dolphin. The diving HR pattern and the presumed rapid N2 washout during the surface-interval tachycardia probably minimized N2 accumulation in the blood during dive sessions.

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