20-Hz pulses and other vocalizations of fin whales, <i>B</i> <i>a</i> <i>l</i> <i>a</i> <i>e</i> <i>n</i> <i>o</i> <i>p</i> <i>t</i> <i>e</i> <i>r</i> <i>a</i> <i>p</i> <i>h</i> <i>y</i> <i>s</i> <i>a</i> <i>l</i> <i>u</i> <i>s</i>, in the Gulf of California, Mexico

Abstract

Low-frequency vocalizations were recorded from fin whales, Balaenoptera physalus, in the Gulf of California, Mexico, during three cruises. In March 1985, recorded 20-Hz pulses were in sequences of regular 9-s interpulse intervals. In August 1987, nearly all were in sequences of doublets with alternating 5- and 18-s interpulse intervals. No 20-Hz pulse sequences of any kind were detected in February 1987. The typical pulse modulated from 42 to 20 Hz and its median duration was 0.7 s (1985 data). Most other fin whale sounds were also short tonal pulses averaging 82, 56, and 68 Hz, respectively, for the three cruises; 89% were modulated in frequency, mostly downward. Compared to Atlantic and Pacific Ocean regions, Gulf of California 20-Hz pulses were unique in terms of frequency modulation, interpulse sound levels, and temporal patterns. Fin whales in the Gulf may represent a regional stock revealed by their sound characteristics, a phenomenon previously shown for humpback whales, birds, and fish. Regional differences in fin whale sounds were found in comparisons of Atlantic and Pacific locations.