A comparison of CTD satellite-linked tags for large cetaceans - Bowhead whales as real-time autonomous sampling

There is an increasing need for comprehensive oceanographic sampling, and taking advantage of marine mammal studies of movements and habitat use for augmenting spatial and temporal coverage, especially in remote and inaccessible areas, is an attractive approach. Oceanographic sampling instruments that transmit profiles of temperature and salinity (CTD) via satellite were deployed on bowhead whales Balaena mysticetus. A novel satellite-linked CTD tag (WC) was compared to an established design (SMRU). The two types of tags were deployed equally on nine bowhead whales in West Greenland. Both tag types used Argos for relaying data and locations, while the WC tag also provided Fastloc-GPS for more accurate locations. One whale carried both tag types. When comparing the two tag types deployed on the same whale, more complete data were obtained from the WC tag in terms of number of profiles, locations and transmissions received, although placement of the tag on the back of the whale and antenna position may have affected some of these parameters. Why transmissions terminated is difficult to determine, however, physical loss of the tag from the whale and mechanical damage to the antenna are the most likely; none of the tags failed because of battery exhaustion. Although, differences in performance of the two tag types were found, we conclude that both satellite-linked CTD tag types deployed on large cetaceans can provide high resolution oceanographic profiles at times and in areas where traditional methods for collecting oceanographic data are logistically difficult and prohibitively expensive.