Underwater Passive Acoustic Monitoring Around Kauai, Hawaii

Abstract

Passive acoustic monitoring is a powerful tool for non-invasive and unbiased data collection in remote locations. The ability to collect data over long durations in areas that are not easily accessible and during all weather conditions has become a common technique for surveying for marine mammals as well as assessing the soundscape that may impact their behavior or distribution. Very little is known about the occurrence of fin (Balaenoptera physalus), sei (Balaenoptera borealis), and Bryde’s (Balaenoptera edeni) whales that are very rarely observed in the coastal waters around the main Hawaiian Islands. This dissertation presents results obtained from underwater passive acoustic data collected at five sites around the island of Kauai, Hawaii, from February 2009 through October 2010. Acoustic files scanned manually to search for sounds produced by fin, sei, and Bryde’s whales. The results corroborate the extremely low sighting rates for these three species. Out of a total 31 acoustic encounters, 18 were from fin whales, 9 were from sei whales, and 4 were from Bryde’s whales. These detections were also compared to those produced by two automated techniques and unfortunately, neither performed well enough to be reliable alternatives to time consuming manual analyses. The broadband acoustic data collected for this study are very useful for determining contributions of natural and anthropogenic sources towards the overall soundscape around Kauai. While fin, sei, and Bryde’s whales were not frequently detected in the data, humpback whale song was ubiquitous during the winter months and was present in nearly each recording from December through March. When comparing the broadband noise levels around Kauai to sites off of Oahu and Nihoa (the closest of the Northwest Hawaiian Islands), it is evident that weather (mainly wind) and shipping noise have the greatest impact on the soundscape.