Under pressure: Effects of instrumentation methods on fur seal pelt function

Tracking marine mammals with electronic devices enables researchers to better understand animal movements and at-sea behavior. For pinnipeds, instruments are typically glued to the animal's hair, either directly to the pelage or via a fabric patch. These instruments are retrieved by cutting the pelage or cutting through the patch. The impact of these modifications to the pelage is presumed to be minimal and short-lived, but this has never been explicitly investigated. This study examined effects of instrument attachment on northern fur seal pelts. To assess thermal consequences of instrumentation, we determined thermal resistance of pelts in water for instruments glued directly to the pelage or with a neoprene base. For each attachment method, we measured the pelt unmodified, with instrument attached, and with instrument removed. Using a hyperbaric chamber, we measured the extent to which water could penetrate the pelt's air layer during diving. Removing the tag by cutting the pelage reduced thermal function of the pelt in water and allowed more air to escape under pressure. In contrast, a neoprene patch better maintained the insulation in water and reduced air loss under pressure. Our results suggest the use of neoprene may reduce negative consequences of instrumentation in fur seals.