Despite years of study, the humpback whale mating system remains an enigma. Sustained observations of subsurface behavior may help reveal important components of the mating system. In 2005 and 2006, we deployed Crittercam, an animal-borne imaging and data-logging tool, on humpback whales in their winter grounds. We focused our efforts on competitive groups, believed to be the epicenter of mate selection. Over 27 days of fieldwork in Maui waters we deployed 10 front- or rear-facing Crittercams on escorts (males) in competitive groups. This work revealed: (1) Five whales swimming to depths of over 150 m, with one animal diving down 298 m; (2) Instances of competitive behavior (inflated pleats, chasing) occurring along the seafloor; (3) The displacement of a primary escort (the whale closest to the female) by a challenger; (4) A detailed time budget of one principal escort maintaining his position over a 73-min observation window; (5) Threats and body strikes between secondary escorts; (6) Apparent affiliative behavior by females, including possible pectoral fin stroking of a principal escort and drafting in a principal escort's pressure wave; and (7) A secondary escort resting on the bottom while sculling its pectoral fins through the substrate, throwing up clouds of sand. In summary, Crittercam allowed us to observe diving behavior and sustained micro-interactions between animals in competitive groups occurring far below the surface. Such observations can have significant bearing on interpretation of the mating system by assisting in uncovering behaviors that may be involved in mate guarding, dominance hierarchies, and female choice.
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