Tags, drifters, and Towfish: Using multiple recording platforms to characterize odontocete acoustic space

Abstract

Bioacoustic tags can reveal novel information about the behavior and ecology of animals on which they are deployed. Yet tags are often placed off the animals’ acoustic axis, limiting some potential analyses. In order to broaden abilities to examine bioacoustic signals and behavior of several Hawaiian odontocetes we adapted recording methods to enhance data collection opportunities and free-field records. While bioacoustic DTAGs were deployed, we also used DMONs (digital acoustic recorders) in both a GPS-outfitted drifter buoy (Drifting Acoustic Wideband Gizmo = DAWG) and a Towfish around pantropical spotted dolphins (Sa), melon-headed whales (Pe), and short-finned pilot whales (Gm). Daytime tag recordings show Pe and Sa were limited to relatively shallow dives (< 50 m) but were relatively soniferous, whereas Gm made occasional deeper dives (to 700 m) and fewer individual calls. Group measures for Pe and Sa from the DAWG and Towfish revealed relatively high incidences of overlapping calls. Preliminary investigations of Pe whistles suggest some limited variation between Pe populations and considerable variability in individual call types. Such characterizations of call rates and variability support efforts to detect and classify odontocete calls. The different methods provided complementary means to collect substantial bioacoustic data on pelagic odontocetes for which few data exist.