Detection of killer whale presence using low duty cycle recorders.

Abstract

Passive aquatic listeners (PALs) have been developed to make long-term (up to a year) autonomous measurements of the underwater ambient noise in the marine environment. Because of data storage limitations and low-power requirements, PALs have a very low duty cycle, of the order of 1 percent. In fact, they are optimized for acoustic rainfall detection and have been successfully used to measure wind speed and rainfall rate at sea using spectral components of the sound field. These geophysical sounds have relatively long time scales (minutes) compared to vocalizations of marine mammals (seconds) or mooring noise (chain clanking). Data collection was designed to detect and reject short temporal signals. However, these signals include marine mammal vocalizations. Consequently, the sampling strategy was modified to evaluate the temporal content of the data sample and save the temporal data sample only if it contains a signal consistent with killer whale vocalizations. These sound bites have demonstrated detection of pod-specific vocalizations of resident-type killer whales, transient-type killer whales, bone crunching from likely killer whale predation (eating) on sea lions, and humpback and N. Pacific right whales.