Seasonal and diurnal pattern of baleen whales detected on the Station Aloha Cabled Observatory off Oahu, Hawaii

Abstract

The ALOHA Cabled Observatory, ACO, located 100 km north of the island of Oahu, Hawaii, includes an acoustic recording package. The hydrophone is at a depth of 4.7 km and is connected to land via an underwater fiber optic cable. Recordings are continuous and made year-round. One year of data, 17 February 2007 to 18 February 2008, were analyzed to detect calls from blue (Balaenoptera musculus), fin (Balaenoptera physalus), sei (Balaenoptera borealis), and minke whales (Balaenoptera acutorostrata). As expected, detections of all four species were highly seasonal with most occurring during the winter months. While the exact migration routes are not well understood for these species, a pattern similar to the breeding/calving migrations of humpback whales would be anticipated. Fin whales were detected most often followed by minke, blue, and sei whales. No diurnal patterns were observed for the fin, sei, and minke whales; however, a diurnal pattern was evident for blue whales (59% of calls were made in the evening and nighttime hours). All of the species are very rarely seen in Hawaiian waters, and blue whales have never been detected during any visual surveys. Acoustics detections are essential for understanding the occurrence of these species in Hawaii.