Listening for Whales at the Station ALOHA Cabled Observatory

Abstract

The Station ALOHA Cabled Observatory (ACO) is an ocean-bottom observatory that allows continuous real-time monitoring of ocean processes including sounds produced by baleen whales. Baleen whales can be challenging to study using traditional visual methods due to their cryptic behavior and offshore ranges. Many baleen whales produce distinctive sounds that propagate well under water and so ocean-bottom hydrophones like the one at the ACO can be used to investigate the occurrence and acoustic behavior of these animals in locations that are difficult to access and study long-term using other methods. We examined 12 months of recordings from the ACO (February 2007–February 2008) and found that sounds produced by blue, sei, and minke whales all occurred seasonally between October and April. Low-frequency pulses produced by fin whales were detected year-round, although much less frequently during the summer months than during the winter months. These seasonal patterns matched those of humpback whales, who migrate to Hawai’ian waters to breed and give birth. Blue, minke, fin, and sei whales are probably using Hawai’ian waters for breeding, but further research is necessary to confirm this. The ACO has provided, and continues to provide, a long-term dataset for investigating seasonal and diurnal trends in the occurrence of baleen whales and other cetaceans at a location that would be difficult to study any other way.