Fur seals do, but sea lions don’t – cross taxa insights into exhalation during ascent from dives

Many agencies provided funding and logistical support for the various research efforts resulting in the data presented here: the South African Department of Science and Technology, administered by the National Research Foundation and the Department of Environmental Affairs for subantarctic fur seal work; the Australian Research Council (DP110102065), Holsworth Wildlife Research Endowment and the Office of Naval Research (Marine Mammals and Biological Oceanography Program Award no. N00014-10-1-0385) for Australian fur seal work; the National Oceanic and Atmospheric Administration (NOAA) via grants to the Alaska SeaLife Center and the National Marine Mammal Laboratory, with additional funding and logistical support from North Pacific Wildlife Consulting for Steller sea lion and northern fur seal (Russia) work; the National Marine Mammal Laboratory, National Marine Fisheries Service, NOAA for northern fur seal (Alaska) work. Research support for R.W. Davis was provided by the National Science Foundation.Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otariid, the Antarctic fur seal (Arctocephalus gazella), then exhales during the final 50–85% of the return to the surface, which may prevent another gas management issue: shallow-water blackout. Here, we compare data collected from animal-attached tags (video cameras, hydrophones and conductivity sensors) deployed on a suite of otariid seal species to examine the ubiquity of ascent exhalations for this group. We find evidence for ascent exhalations across four fur seal species, but that such exhalations are absent for three sea lion species. Fur seals and sea lions are no longer genetically separated into distinct subfamilies, but are morphologically distinguished by the thick underfur layer of fur seals. Together with their smaller size and energetic dives, we suggest their air-filled fur might underlie the need to perform these exhalations, although whether to reduce buoyancy and ascent speed, for the avoidance of shallow-water blackout or to prevent other cardiovascular management issues in their diving remains unclear.PostprintPostprintPeer reviewe