[MARMAM] Two papers on deep diving, pelagic bottlenose dolphins

Andreas afahlman at whoi.edu
Tue Jul 17 02:14:10 PDT 2018

Dear All,

We are pleased to announce that the following two papers have been published looking at resting metabolic rate, lung function (article 1) and theoretical blood and tissue gas tensions (article 2) in free-ranging bottlenose dolphin

Article 1: Fahlman A, McHugh K, Allen J, Barleycorn A, Allen A, Sweeney J, Stone R, Faulkner Trainor R, Bedford G, Moore MJ, Jensen FH, and Wells R (2018) Resting Metabolic Rate and Lung Function in Wild Offshore Common Bottlenose Dolphins, Tursiops truncatus, Near BermudaFront. Physiol. 9:886. doi: 10.3389/fphys.2018.00886

URL: https://www.frontiersin.org/articles/10.3389/fphys.2018.00886/full

Diving mammals have evolved a suite of physiological adaptations to manage respiratory gases during extended breath-hold dives. To test the hypothesis that offshore bottlenose dolphins have evolved physiological adaptations to improve their ability for extended deep dives and as protection for lung barotrauma, we investigated the lung function and respiratory physiology of 4 wild common bottlenose dolphins (Tursiops truncatus) near the island of Bermuda. We measured blood haematocrit (Hct, %), resting metabolic rate (RMR, l O2 min-1), tidal volume (VT, l), respiratory frequency (fR, breaths min-1), respiratory flow (l min-1), and dynamic lung compliance (CL, l cmH2O-1) in air and in water, and compared measurements with published results from coastal, shallow-diving dolphins. We found that offshore dolphins had greater Hct (56±2%) compared to shallow-diving bottlenose dolphins (range: 30-49%), thus resulting in a greater O2 storage capacity and longer aerobic diving duration. Contrary to our hypothesis, the specific CL (sCL, 0.30 ± 0.12 cmH2O-1) was not different between populations. Neither the mass-specific RMR (3.0±1.7 ml O2 min-1 kg-1), nor VT (23.0 ± 3.7 ml kg-1) were different from coastal ecotype bottlenose dolphins, both in the wild and under managed care, suggesting that deep-diving dolphins do not have metabolic or respiratory adaptations that differs from the shallow-diving ecotypes. The lack of respiratory adaptations for deep diving further support the recently developed hypothesis that gas management in cetaceans is not entirely passive but governed by alteration in the ventilation-perfusion matching, which allows for selective gas exchange to protect against diving related problems such as decompression sickness.

Article 2: 

Fahlman A, Jensen FH, Tyack PL and Wells RS (2018) Modeling Tissue and Blood Gas Kinetics in Coastal and Offshore Common Bottlenose
Dolphins, Tursiops truncatus. Front. Physiol. 9:838. doi: 10.3389/fphys.2018.00838

URL: https://www.frontiersin.org/articles/10.3389/fphys.2018.00838/full

Bottlenose dolphins are highly versatile breath-holding predators that have adapted to a wide range of foraging niches from rivers and coastal ecosystems to deep-water oceanic habitats. Considerable research has been done to understand how dolphins manage O2 during diving, but little information exists on other gases or how pressure affects gas exchange. Here we used a dynamic multi-compartment gas exchange model to estimate blood and tissue O2, CO2 and N2 from high-resolution dive records of two different common bottlenose dolphin (Tursiops truncatus) ecotypes inhabiting shallow (Sarasota Bay) and deep (Bermuda) habitats. The objective was to compare potential physiological strategies used by the two populations to manage shallow and deep diving life styles. We informed the model using species-specific parameters for blood hematocrit, resting metabolic rate, and lung compliance. The model suggests that the known O2 stores were sufficient for Sarasota Bay dolphins to remain within the calculated aerobic dive limit (cADL), but insufficient for Bermuda dolphins that regularly exceeded their cADL. By adjusting the model to reflect the body composition of deep diving Bermuda dolphins, with elevated muscle mass, muscle myoglobin concentration and blood volume, the cADL increased beyond the longest dive duration, thus reflecting the necessary physiological and morphological changes to maintain their deep-diving life-style. The results indicate that cardiac output had to remain elevated during surface intervals for both ecotypes, and suggests that cardiac output has to remain elevated during shallow dives in-between deep dives to allow sufficient restoration of O2 stores for Bermuda dolphins. Our integrated modelling approach contradicts predictions from simple models, emphasising the complex nature of physiological interactions between circulation, lung compression and gas exchange.

Please email me (afahlman at whoi.edu) if you would like a PDF copy of the paper or if you have any questions regarding the work.

Best regards,

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