Using suction-cup attached time-depth recorder/VHF radio tags, we documented the diving behavior of humpback whales off the west side of Maui, Hawaii. Between February and April 2000, tags were deployed on 15 individuals, and dive data were obtained from 13 of the 14 tags recovered. Reactions to tagging were observed less often than has been documented for biopsy darting, and were generally short-term. A total of 62 hours of dive data were obtained. All tagged whales were known or thought to be adult or sub-adult males, and most were involved in competitive groups for all or part of the time tags were attached. In many cases, dive depths were potentially limited by bottom depth, that is, many tagged whales were found in relatively shallow (<100 m bottom depth) water for all (n=5) or part (n=5) of the time tags were attached. Maximum dive depth was 176 m, and dives greater than 100 m in depth occurred an average of 1.37 times per hour (SD=2.35). Some of these deep dives were to the bottom. Excluding periods when tagged whales were known to be in less than 100 m of water, dives to over 100 m occurred an average of 1.73 times per hour (SD=2.52). Where the whales spent their time in the water column varied considerably between individuals. Whales that had modal depth distributions between 10 and 30 m spent some of their time apparently motionless at depth, a behavior similar to that documented for singing humpbacks. Most whales in competitive groups and one escort to a mother/calf pair spent the majority of their time in the top 10 m of the water column, while two individuals in competitive groups spent a substantial proportion of their time (10% and 29%) at depths greater than 100 m. We discuss a variety of factors that potentially influence diving behavior, including the presence of a calf within the group, time of day, and behavioral role. Management implications of dive data, including aerial survey calibration factors and exposure to depth-specific threats, are also discussed.
Citation:
Baird, R.W., A.D. Ligon, and S.K. Hooker. 2000. Sub-Surface and Night-Time Behavior of Humpback Whales off Maui, Hawaii: A Preliminary Report. Report prepared under Contract #40ABNC050729 from the Hawaiian Islands Humpback Whale National Marine Sanctuary, Kihei, HI, to the Hawaii Wildlife Fund, Paia, HI.
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