Reduced venous oxygen depletion in response to at-sea acoustic disturbance in diving northern elephant seals

Abstract

Marine mammals face increased human activities in the ocean, including shipping, recreation, and seismic exploration. Such disturbances may alter short-term behavior and long-term life history patterns; however, many of the mechanistic details of responses remain unknown. Because marine mammals survival depends on their diving abilities, physiological specializations to diving will likely define the scope of underwater responses to a disturbance. Prior research in aquatic animals has demonstrated an increased bradycardia in response to underwater stressors. We examined cardiovascular physiological responses to disturbances at sea in freely diving juvenile northern elephant seals ( Mirounga angustirostris). We predicted that, after an acoustic disturbance at sea, seals would intensify the dive response, resulting in reduced whole-body oxygen (O 2 ) consumption and slower venous O 2 depletion. To test this hypothesis, we recorded venous P O2 and diving behavior in translocated juvenile northern elephant seals that were exposed to experimental acoustic disturbances while freely diving at sea. Venous P O2 was measured in the extradural vein using a Clark polarographic electrode attached to a biologger. After being exposed to an acoustic noise during the ascent phase of deep dives, seals typically exhibited an immediate inversion of the dive, descending to deeper depths. Dives with acoustic disturbances were significantly longer than dives prior to the acoustic disturbance (24.8 ± 6.2 mins vs 19.1 ± 2.9 mins). Although the magnitude of P O2 depletion was not significantly different between pre-disturbance dives and disturbed dives (52.6 ± 21.6 mmHg vs 53.5 ± 20.8 mmHg, n= 27 paired dives), the depletion rate was slower in disturbed dives. In dives prior to the disturbance, P O2 depletion was 3.2 ± 1.5 mmHg min -1 , but in dives with a disturbance, P O2 depletion was 2.5 ± 1.3 mmHg min -1 . This reduction in venous P O2 depletion rate suggests O 2 consumption during disturbed dives may be similar to the amount consumed during non-disturbed dives. This reduction may be a result of altered perfusion, including reduced muscle blood flow. In particular, reduced perfusion to working muscle would likely reduce O 2 extraction, and may be a key factor in fine-tuning the dive response after a disturbance to conserve O 2 for the brain and heart. National Science Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.