Estimating relative abundance of singing humpback whales in Los Cabos, México, using diffuse ambient noise

• Published in: The Journal of the Acoustical Society of America 2014-10, Vol.136 (4_Supplement), p.2247-2247
• Main Authors: Seger, Kerri, Thode, Aaron M., López Arzate, Diana C., Urbán, Jorge
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4900113

Previous research has speculated that diffuse ambient noise levels can be used to estimate relative cetacean abundance in certain locations when baleen whale vocal activity dominates the soundscape (Au et al., 2000; Mellinger et al., 2009). During the 2013 and 2014 humpback whale breeding seasons off Los Cabos, Mexico, visual point and line transects were conducted alongside two bottom-mounted acoustic deployments. As theorized, preliminary analysis of ambient noise between 100 and 1,000 Hz is dominated by humpback whale song. It also displays a diel cycle similar to that found in the West Indies, Australia, and Hawai’i, whereby peak levels occur near midnight and troughs occur soon after sunrise (Au et al., 2000; McCauley et al., 1996). Depending upon site and year, the median band-integrated levels fluctuated between 7 and 16 dB re 1 uPa when sampled in one hour increments. This presentation uses analytical models of wind-generated noise in an ocean waveguide to analyze potential relationships between singing whale density and diffuse ambient noise levels. It explores whether various diel cycle strengths (peak-to-peak measurements and Fourier analysis) correspond with trends observed from concurrent visual censuses. [Work sponsored by the Ocean Foundation.]