Introduction & Objectives

Passive acoustic monitoring was conducted in the Gulf of Alaska Temporary Maritime Activities Area (GOA TMAA) from 2011 to 2019 in order to record the low-frequency ambient soundscape and detect marine mammal and anthropogenic sounds during times of naval exercises in the area. The objectives were to determine what species and populations of marine mammals were present and to establish a baseline for vocalization behavior in the region. 

Technical Approach

High-frequency Acoustic Recording Packages (HARPs) recorded sounds between 10 Hz and 100 kHz on a duty cycle to increase deployment and recording duration.  The number of HARPs ranged from two to five per deployment at seven locations throughout the duration of this study.  These locations included continental shelf, continental slope, deep water, and seamount sites throughout the GOA TMAA. 

Recorded data were analyzed for marine mammal sounds, anthropogenic sounds, and ambient sound levels.  For marine mammal and anthropogenic sounds, data analysis consisted of detecting sounds by analyst visual scans of long-term spectral averages (LTSAs) and spectrograms, and by automated computer algorithm detection when possible.

Progress & Results

Five baleen whale species were recorded: blue, fin, gray, North Pacific right, and humpback whales.  Blue whales and fin whales were the most commonly detected baleen whales in these recordings. Blue whales B call calls were the most common blue whale call type detected and peaked during the fall. Blue whale D calls were highest during the spring and summer. The fin whale acoustic index (representative of 20 Hz calls) was low throughout the summer and began to increase in August. Meanwhile, fin whale 40 Hz calls were seen throughout the recordings. Humpback whales were detected only during the winter and early spring.

Signals from eight known odontocete species were recorded: Risso’s dolphins, Pacific white-sided dolphins, killer whales, sperm whales, Baird’s beaked whales, Cuvier’s beaked whales, Stejneger’s beaked whales, and unidentified porpoise.  Sperm whales, Cuvier’s beaked whales, and Stejneger’s beaked whales were most consistently detected across sites and years. 

Four anthropogenic signals were detected: mid-frequency active (MFA) sonar, low-frequency active (LFA) sonar, explosions, and broadband ship noise. Ambient soundscape was also described for 2011-2015 and 2015-2017.  MFA and LFA sonar detections were compared against Navy records of sonar use, resulting in some matches and other events not associated with U.S. Navy sonar use.  Explosions were most commonly detected during summer and were not associated with U.S. Navy training events. 

Publications:

Rice, A. A. Sirovik, J. S. Trickey, A. J. Debich, R. S. Gottleb, S. M. Wiggins, J. A. Hildebrand, S. Baumann-Pickering. 2021. Cetacean occurrence in the Gulf of Alaska from long-term passive acoustic monitoring. Marine Biology. 168:72. https://doi.org/10.1007/s00227-021-03884-1