Analysis of melon-headed whale aggregation in Hanalei Bay, July 2004

On 3 July 2004, an aggregation of ca. 150–200 melon-headed whales (Peponocephala electra) appeared in the shallow waters of Hanalei Bay, Kauai and congregated there for over 27 h. Preceding the whales’ appearance and partially coincident with their time in the Bay, midrange (3.5–5 kHz) tactical sonars were intermittently deployed during the Rim of the Pacific 2004 (RIMPAC) joint military exercises being conducted in waters near Kauai by the U.S., Japan, and Australia Navies. An NOAA report (Southall et al., 2006) attributed the active sonar usage as a plausible, if not likely, contributing factor. A detailed timeline and reconstruction of the RIMPAC activities is presented showing the worst-case estimates of the sonar sound levels in the waters surrounding Kauai. A re-examination of available evidence combined with a new report of a simultaneous and similar aggregation in Sasanhaya Bay, Rota, Commonwealth of the Northern Mariana Islands, brings the plausibility conclusion into question. [This work was sponsored by multiple sources. D. Fromm and S. Martin conducted acoustic analyses with funds provided by the U.S. Pacific Fleet. J. Mobley received funding from the U.S. Geological Survey. P. Nachtigall is sponsored by the Office of Naval Research for marine mammal audiometric studies.]