Introduction & Objectives

A cetacean survey using passive-acoustic gliders was conducted in the Mariana Islands Range Complex in support of monitoring requirements. The objectives of the study were to determine what species of toothed whales and baleen whales occur in the MIRC and to examine their spatial and seasonal distribution in offshore areas.

Technical Approach

An autonomous underwater vehicle called the Seaglider was equipped with a custom-designed and custom-built passive acoustic recording system developed by the University of Washington.  The glider was capable of diving repeatedly to a depth of 1000 meters and operate for over one month.  The glider was programmed to survey across diverse bathymetric features and cetacean habitats whenever possible.  The acoustic recorder continuously recorded sounds from 15 Hz to 90 kHz, allowing for identification of sounds from most species with the exception of pygmy and dwarf sperm whales (Kogia species).  Each glider also recorded position, standard conductivity, temperature, and depth profiles which were transmitted via Iridium satellite link when surfacing between dives. The acoustic recordings were analyzed once the gliders were recovered for presence of marine mammal species and relative occurrence. 

Progress & Results

Two surveys conducted by two gliders each occurred from 19 September to 14 November 2014 and 2 March to 27 April 2015.  The 2014 deployments (one instrument malfunction) covered a distance of 833 km and recorded 749 hours of acoustic data.  Acoustic encounters included Blainville’s beaked whales, killer whales, Risso’s dolphins, sperm whales, unidentified beaked whale, and unidentified baleen whale.  The 2015 deployments covered a distance of 1400 km and recorded 1388 hours of acoustic data.  Acoustic encounters included Blainville’s beaked whales, Cross Seamount beaked whales, sperm whales, Risso’s dolphins, delphinids, fin whales, humpback whales, minke whales, and unidentified sounds.  Navy sonar sounds were also identified. 

Publications 

A complex baleen whale call recorded in the Mariana Trench Marine National Monument