Modelling the effect of varying metabolic rate and cardiac output on estimated tissue and blood O ₂ and CO ₂ levels in an extreme deep‐diver, the goose‐beaked whale ( <i>Ziphius cavirostris</i> )

High-resolution movement data from Cuvier's beaked, or goose-beaked whale (Ziphius cavirostris, hereafter Ziphius, n = 8) tag deployments (4.1-19.2 days) were used to estimate blood and tissue O₂ and CO₂ levels. Acceleration and magnetometry data were used to estimate the locomotion cost (LC) from the relationship between activity and the O₂ consumption rate. We estimated that the diving metabolic rate (DMR) decreased with increasing dive duration, ranging from 6.18 mL O₂ min^-1 kg^-1 for very short dives (<1.0 min) to 1.65 mL O₂ min^-1 kg^-1 and 2.06 mL O₂ min^-1 kg^-1 for intermediate (>17.5 and ≤33.3 min) and long dives (>33.3 min), respectively. The calculated aerobic dive limit (cADL), average behavioural ADL (bADL) and dynamic ADL (dADL) were 62.4, 61.3 (44.3-75.4) and 41.7 (2.0-102.5) min, respectively. Despite the physiological and metabolic adjustments assumed by the model, the muscle O₂ ran out for many of the stereotypical long, deep dives exhibited by these animals. Based on the model results, we speculate that a large portion of the foraging dives in Ziphius are fuelled by alternative metabolic pathways, for example, phosphocreatine or glycolysis. A reliance on these alternative metabolic pathways during foraging may require long recovery periods, including primarily aerobic dives. Disturbing this normal dive pattern may disrupt this normal dive pattern, leading to behavioural and physiological changes that could cause trauma.