Introduction & Objectives

The Navy’s Southern California (SOCAL) Range Complex is located in the Southern California Bight and the adjacent deep waters to the west. A diverse array of marine mammals is found here, including baleen whales, beaked whales, and other toothed whales and pinnipeds.  In January 2009, an acoustic monitoring effort was initiated within the SOCAL Range Complex. 

The goal of this effort was to characterize the vocalizations of marine mammal species present in the area, determine their seasonal presence, and evaluate the potential for impact from naval training. Since 2009, efforts have been expanded to explore the seasonal presence of a subset of species of particular interest, including blue whales, fin whales, and beaked whales. In addition, the low-frequency ambient soundscape, as well as the presence of MidFrequency Active (MFA) sonar and explosions have been analyzed.

Technical Approach

High-frequency Acoustic Recording Package (HARP): HARPs were used to record the low-frequency ambient soundscape as well as marine mammal and anthropogenic sounds in the SOCAL area. HARPs can autonomously record underwater sounds from 10 Hz up to 160 kHz and are capable of up to approximately one year of continuous data storage.

Data Collected: Acoustic recordings have been collected within the SOCAL Range Complex near San Clemente Island since 2009 using HARPs sampling at 200 kHz.

Data Analysis: Recording over a broad frequency range of 10 Hz to 100 kHz allows quantification of the low-frequency ambient soundscape, detection of baleen whales (mysticetes), toothed whales (odontocetes), and anthropogenic sounds. Analyses were conducted using appropriate automated detectors for whale and anthropogenic sound sources. 

Progress & Results

2021 progress & results:

Two anthropogenic pulsed signals were detected: MFA sonar and explosions. MFA sonar was detected at all sites with peaks in February, August, and November 2019. Explosions were detected at all sites, but were highest in October and November 2019 and February 2020, temporal and spectral parameters suggest primarily association with fishing, specifically with the use of seal bombs. 

Calls of two baleen whale species were detected: blue whale B calls and fin whale 20 Hz calls. Both species were present at all sites: blue whale B calls were highest at site E and the fin whale acoustic index, representative of 20 Hz calls, was highest at site E and lowest at site U. Blue whale B call detections peaked in August 2019 and again in October 2019 at sites H and N. Very few blue whale B calls were detected after January 2020. The fin whale acoustic index was highest from October 2019 to April 2020. 

Frequency modulated (FM) echolocation pulses from Cuvier’s beaked whales were regularly detected at all sites, but were detected in much higher numbers at sites E and H. At site E, detections were highest in December 2019, while at site H they peaked in August 2019 and again from February to May 2020.