Title

Underwater behavior of humpback whales in a western North Atlantic foraging area

Abstract

In July of 2004 we used synchronous motion, digital acoustic recording tags (DTAGs) to investigate the underwater behavior of humpback whales in the Great South Channel. Tag attachments to four animals resulted in ~50 hours of data in water depths from 70 - 90m. We conducted a detailed analysis of dive patterns, including apparent bottom feeding and associated sounds. We partitioned dive records into 3 categories: descent, ascent, and at-depth. All four animals traversed a majority of the descent in freeglide (86%, 78%, 84%, and 70%), and fluke-strokes were confined to the upper portions of the water column [ending at: -11.2 m (0.22), -16.1 m (2.9), -12.0 m (2.9), -25.5 m (6.8)]. On ascent, fluke-strokes were in much more of the water column [ending at: -19.9 m (2.4), -39.6 m (11.0), -24.4 m (6.0), -28.6 m (5.6)], but animals still traversed a substantial portion in free-glide (24%, 54%, 33%, and 33%). Thus, descent and ascent demonstrated buoyancy related adaptations for locomotor efficiency. At-depth behavior consisted primarily of presumed foraging activity. In 95% of flat-bottomed dives whales exhibited a characteristic “side-roll” behavior. Side-rolls involved the animal rolling laterally more than 40º from dorsal and holding that position for a consistent duration, usually more than 10 seconds. Mean number of side-rolls per dive for each animal was 2.84, 6.7, 3.15, and 4.32. Two animals had a consistent mean sideroll duration (in seconds), while mean duration for the other two was more varied [17.7 s (4.0), 24.6 s (11.5), 13.1 s (2.6), 19.1 s (14.4)]. For each animal the angle of roll was consistent [96.7º (7.7), -73º (17.6), - 80.5º (3.7), -84.2º (23)], and they maintained a head-down pitch angle [28.5º (3.2), 24.4º (9.3), 10.7º (4.8), 32.2º (2.6)]. Between side-rolls, animals returned to a dorsal-ventral orientation. Side-rolls occurred at or within a few meters of the sea floor and were often preceded by a stereotypic sound. We speculate that side-rolls indicate periods of consumatory feeding. Data have management implications with regards to whale entanglement and fishing gear modification.

Publication Date

12-2005

Journal or Conference Title

Biennial Conference on the Biology of Marine Mammals (CBMM)

Conference Date

Dec 12 - Dec 16, 2005

Publisher Place

San Diego, CA, USA

Document Type

Conference Proceeding

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