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Post-dive gas recovery and the transition between metabolic states as physiological limits to diving in Steller sea lions (Eumetopias jubatus) Purdy, Aaron Scott

Abstract

Marine mammal diving behaviour is influenced by multiple physiological processes, both at depth and at the surface. To date, the majority of research in diving physiology has focused solely on how quickly marine mammals utilize their O₂ during a dive, as seen in the numerous studies of the aerobic dive limit (ADL) and calculated aerobic dive limit (cADL). In this thesis I investigated other physiological limits, namely how long it takes for marine mammals to recover after a dive, and how these animals transition between aerobic and anaerobic metabolism at depth. Specifically, I 1) determined how post-dive rates of O₂ and CO₂ gas exchange are affected by dive behaviour, and 2) measured how lactate accumulates with increased dive time, and examined how this indicator of metabolic transition affected post-dive recovery times. To measure gas exchange, I used flow-through respirometry to determine the time required for Steller sea lions (Eumetopias jubatus) to reach within 5% of stable rates of O₂ uptake and CO₂ excretion following a dive. These times were interpreted as the O₂ and CO₂ recovery times, respectively. CO₂ recovery time was longer and became more extended with increasing dive time when compared to O₂, requiring an extra 44 sec per minute submerged for CO₂ as opposed to 33 sec per minute submerged for O₂. This indicates that recovery time was limited by CO₂ as opposed to O₂, and this difference became greater with increased dive time. Contrary to traditional models, plasma lactate concentration was present even after short dives, and increased linearly with dive duration. Neither O₂ nor CO₂ recovery rates were affected by levels of blood lactate. This indicates that anaerobic metabolism may be used long before the body’s total O₂ -stores have been consumed. These results support the idea that there is not a distinct threshold between aerobic and anaerobic pathways, but rather a progressive transition, which casts doubt on the usual interpretations of the ADL and cADL. My thesis challenges long-held assertions in diving physiology, and underlines the need to further examine how CO₂ and lactate accumulation may act as limits to diving behaviour.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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