Swim speed and acceleration measurements of short-finned pilot whales (Globicephala macrorhynchus) in Hawai‘i
Sakai, M., K. Aoki, K. Sato, M. Amano, R.W. Baird, D.L. Webster, G.S. Schorr and N. Miyazaki. 2011. Swim speed and acceleration measurements of short-finned pilot whales (Globicephala macrorhynchus) in Hawai‘i. Mammal Study 36:55-59.
Over the last few years, studies of top predators in marine ecosystems have benefited from the use of biologging systems (Naito 2004; Rutz and Hays 2009). For example, researchers use these techniques to study animal foraging tactics and diving physiology by analyzing acceleration (body angle and stroke), and parameters such as swim depth and swim speeds (e.g., Sato et al. 2003, 2007; Sakamoto et al. 2009). Short-finned pilot whale (Globicephala macrorhynchus), a top predator, is found worldwide in tropical and warm temperate waters. Mature males are from 4.5 to 7 m in length and mature females are from 3.5 to 5 m in length (Bernard and Reilly 1999). Previous studies suggested they are foraging during deep dives which cannot be observed visually. Their primary prey are squid and in Hawai‘i they are known to make deep dives (600–800 m) during the day, but also spend considerable periods of time shallow diving or surface resting during the day (Baird et al. 2003). Amano and Baird (1998) recorded deep dives over 100 m off Japan. Soto et al. (2008) recorded sound, depth, and orientation from tri-axial accelerometers and magnetometers, and suggested prey chasing behavior by analyzing vertical speed and sound emission during deep dives. For a better understanding of foraging tactics and diving physiology of this species, for example studying prey pursuit in a horizontal direction, stroking patterns and body angle, or assessing behavior by acceleration, we need to record acceleration and swim speed simultaneously. However, swim speed for short-finned pilot whales has not yet been recorded. We used remotely deployed suction-cup tags for measuring swim speed and acceleration of short-finned pilot whales. The understanding of toothed whale behavior has been advanced by using suction-cup attached data loggers (for a review see Hooker and Baird 2001). There are several types of suction-cup attached tag: one attached with multiple suction-cups that fixed a data logger in place (e.g., Soto et al. 2008), which with a single suction-cup connected to a data logger with a flexible plastic tube (Baird et al. 2005), and one with a single suction-cup that fixed a data logger in place. With remotely-deployed tags, it is difficult to set the tag parallel to the water flow. Therefore it would be hard to record swim speed using a propeller with a multiple suction-cup tag. A tag using a flexible plastic tube cannot record acceleration caused by the animal precisely because it is not fixed on the animal’s body. A tag fixed on a suction-cup has been demonstrated to record swim speed and acceleration simultaneously in previous studies (finless porpoises, Neophocaena phocaenoides, Akamatsu et al. 2005; sperm whales, Physeter macrocephalus, Aoki 2008). The purpose of our work was to determine whether this type of suction cup tag is appropriate for studying swim speed and acceleration in short-finned pilot whales, and whether it was possible to determine behavior types based on the data collected.