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

2025 progress & results:

Passive acoustic monitoring was conducted in the Navy’s Southern California (SOCAL) Range Complex from August 2023 to December 2024 to detect marine mammal and anthropogenic sounds. A new monitoring site was established offshore Morro Bay. 

2024 progress & results:

Passive acoustic monitoring was conducted in the Navy’s Southern California (SOCAL) Range Complex from May 2022 to July 2023 to detect marine mammal and anthropogenic sounds. The underwater ambient soundscape at all sites had spectral shapes with higher levels at low frequencies owing to the dominance of ship noise and whale calls at frequencies below 100 Hz and local wind and waves above 100 Hz. Prominent peaks in sound spectrum levels observed in the frequency band 15–30 Hz during fall and winter at all sites were related to the seasonally increased presence of fin whale calls. Spectral peaks around 42 Hz from July to December at all sites were related to blue whale B calls. Cuvier’s beaked whales were the only cetacean species monitored during this reporting period. Cuvier’s beaked whales were detected throughout all four sites. 

MFA sonar was a commonly detected anthropogenic sound. The dates of major naval training exercises that were conducted in the SOCAL region between May 2022 and July 2023 were analyzed. Notably, the majority of MFA sonar was detected outside of periods when training exercises occurred. Explosions occurred throughout the monitoring periods at all sites. Cumulatively, 2,220 explosive events were detected during this reporting period. 

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.

Publications:

Bloom, S.G., M.N. Alksne, A. Rice, M. Lankhorst, A. Širović, J.D. Warren, and S. Baumann-Pickering. 2025. Seasonal changes in physical oceanography modulate cetacean predator–prey dynamics in the San Diego Trough. Marine Ecology Progress Series 762:111–133.

ZoBell, V.M., N. Posdaljian, K.L. Lenssen, S.M. Wiggins, J.A. Hildebrand, S. Baumann-Pickering, and K.E. Frasier. 2025. Climatic and economic fluctuations revealed by decadal ocean soundscapes. The Journal of the Acoustical Society of America 157(6):4233–4251.

Alksne, M.N., A.C.M. Kok, A. Agarwal, K.E. Frasier, and S. Baumann-Pickering. 2024. Biogeographic patterns of Pacific white-sided dolphins based on long-term passive acoustic records. Diversity and Distributions 30:e13903.

Arrieta, G.M., S.M. Wiggins, K.K. Cohen, B.J. Thayre, A. Širović, and S. Baumann-Pickering. 2024. Calling behavior and localization of blue whales in Southern California. Detection, Classification, Localization, and Density Estimation of Marine Mammals using Passive Acoustics. June 3–7, 2024. Rotterdam, The Netherlands.

Schoenbeck, C.M., A. Solsona-Berga, P.J.S. Franks, K.E. Frasier, J.S. Trickey, C. Aguilar, I.D. Schroeder, A. Širović, S.J. Bograd, G. Gopalakrishnan, and S. Baumann-Pickering. 2024. Ziphius cavirostris presence relative to the vertical and temporal variability of oceanographic conditions in the Southern California Bight. Ecology and Evolution 14:e11708.

Rice, A., A. Širović, J.A. Hildebrand, M. Wood, A. Carbaugh-Rutland, and S. Baumann-Pickering. 2022. Update on frequency decline of Northeast Pacific blue whale (Balaenoptera musculus) calls. PLoS ONE 17(4):e0266469.

Baumann-Pickering, S., J.S. Trickey, A. Širović, C.S. Oedekoven, J.A. Hildebrand, L. Thomas, S.M. Wiggins, and M.A. Roch. 2018. Impact of mid-frequency active sonar on beaked whale echolocation from long-term passive acoustic recordings. Abstracts, ESOMM-2018, 6th International Meeting on the Effects of Sounds in the Ocean on Marine Mammals, The Hague, The Netherlands, 9-14 September 2018.