Journal of Experimental Biology - Latest Issue

• Gas exchange dynamics in bottlenose dolphins around 2 min apneas conform to values for terrestrial mammals

  ABSTRACT

  Cetaceans are often assumed to employ very high oxygen extractions of ∼40–60% and high tidal volumes (60–80% of vital capacity) to decrease surface time and increase foraging time at depth. However, such oxygen extractions and tidal volumes are greatly at odds with gas exchange in terrestrial mammals, and may, if incorrect, lead to severe overestimations of field metabolic rate (FMR) in wild animals when modeling oxygen uptake from respiration rates. Here, we tested the hypothesis that bottlenose dolphins have such high average oxygen extractions and tidal volumes. By measuring oxygen extractions and tidal volumes of >2000 breaths before and after a 2 min apnea bout in three trained bottlenose dolphins, we show that average pre-apnea resting oxygen extractions are between 17% and 25%, less than half of what has historically been reported for cetaceans. Following apnea, initial oxygen extractions are high (∼60%) but drop below pre-apnea levels in 11–20 breaths. Tidal volumes in this experimental setting were between 21% and 37% of vital capacity, consistent with recent findings for marine mammals, but less than half the 60–80% often assumed for cetaceans in FMR modeling. We therefore reject the hypothesis that bottlenose dolphins on average employ high oxygen extractions and high tidal volumes at rest and following short apneas. Consequently, using fixed high values for tidal volumes and oxygen extractions when modeling FMR from breathing rates in wild cetaceans may possibly lead to overestimations of their energy expenditure, food requirements and ecological roles.

• Stanford's Hopkins Marine Station: insights into the purpose, promise and peril of field stations

  ABSTRACT

  Hopkins Marine Station, Stanford University's marine science center, exemplifies five attributes that could be said to characterize field stations in general: history, location, isolation, focus and fragility. Founded in 1892, the Marine Station has a long history of notable research on subjects ranging from the biochemistry of photosynthesis to developmental biology, intertidal ecology and comparative physiology. Five Nobel laureates have been influenced by classes they attended at Hopkins, and the nearly 700 undergraduate research projects conducted at the Marine Station have sparked seminal studies on subjects as disparate as marine pollution and climate change. Current research spans topics from environmental DNA to the conservation of fisheries and the biomechanics of foraging whales. The Marine Station's scientific and educational goals are facilitated by its location on the edge of Monterey Bay and its isolation from the university's main campus, which combine to encourage a sense of intellectual community and a productive focus on the marine environment and its inhabitants. However, Hopkins' location and isolation do pose their own risks. As with most field stations, isolation from the main campus has at times made the Marine Station vulnerable to closure when money was tight, and owing to its proximity to the shore, sea-level rise poses an existential threat. In these times of rapid environmental and societal change, it is important to recognize both the value and the fragility of field institutions such as Hopkins Marine Station.