Seasonal variability and detection range modeling of baleen whale calls in the Gulf of Alaska, 1999-2002.

Five species of large whales, including the blue (Balaenoptera musculus), fin (B. physalus), sei (B. borealis), humpback (Megaptera novaeangliae), and North Pacific right (Eubalaena japonica), were the target of commercial harvests in the Gulf of Alaska (GoA) during the 19th through mid-20th Centuries. Since this time, there have been a few summer time visual surveys for these species, but no overview of year-round use of these waters by endangered whales primarily because standard visual survey data are difficult and costly. From October 1999-May 2002, moored hydrophones were deployed in six locations in the GoA to record whale calls. Reception of calls from fin, humpback, and blue whales and an unknown source, called Watkins' whale, showed seasonal and geographic variation. Calls were detected more often during the winter than during the summer, suggesting that animals inhabit the GoA year-round. To estimate the distance at which species-diagnostic calls could be heard, parabolic equation propagation loss models for frequencies characteristic of each of each call type were run. Maximum detection ranges in the subarctic North Pacific ranged from 45 to 250 km among three species (fin, humpback, blue), although modeled detection ranges varied greatly with input parameters and choice of ambient noise level.

Types, distribution, and seasonal occurrence of sounds attributed to Bryde's whales (Balaenoptera edeni) recorded in the eastern tropical Pacific, 1999-2001.

Vocalizations resembling known Bryde's whale sounds were recorded on autonomous hydrophones at seven sites in the eastern tropical Pacific. Five short (<3 s) low-frequency (<80 Hz) "phrase" types were observed. "Swept alternating tonal" phrases included a 37-Hz tone and often a 25-16-Hz downswept tone, while "nonswept alternating tonal" phrases had a predominant tone at 29 Hz and often additional tones at 16 and 47 Hz. Alternating tonal phrases were found in 79% of the total hours in which phrases were detected, and occurred primarily at the eastern hydrophone sites. "Burst-tonal" phrases included tones that were often preceded by a wideband burst of noise. The "low burst-tonal" phrase contained tones at 19 and 30 Hz, and was detected at five of the hydrophone sites. The "high burst-tonal" phrase included a 42-Hz tone and was observed only on the northwestern hydrophones. A single "harmonic tone" phrase type was observed that included a fundamental tone at 26 Hz and at least two harmonics; this phrase was observed exclusively at the eastern hydrophone stations. This opportunistic survey has shown that acoustics is an effective means of studying this poorly understood, pelagic balaenopterid.

Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean.

Beginning in February 1999, an array of six autonomous hydrophones was moored near the Mid-Atlantic Ridge (35 degrees N-15 degrees N, 50 degrees W-33 degrees W). Two years of data were reviewed for whale vocalizations by visually examining spectrograms. Four distinct sounds were detected that are believed to be of biological origin: (1) a two-part low-frequency moan at roughly 18 Hz lasting 25 s which has previously been attributed to blue whales (Balaenoptera musculus); (2) series of short pulses approximately 18 s apart centered at 22 Hz, which are likely produced by fin whales (B. physalus); (3) series of short, pulsive sounds at 30 Hz and above and approximately 1 s apart that resemble sounds attributed to minke whales (B. acutorostrata); and (4) downswept, pulsive sounds above 30 Hz that are likely from baleen whales. Vocalizations were detected most often in the winter, and blue- and fin whale sounds were detected most often on the northern hydrophones. Sounds from seismic airguns were recorded frequently, particularly during summer, from locations over 3000 km from this array. Whales were detected by these hydrophones despite its location in a very remote part of the Atlantic Ocean that has traditionally been difficult to survey.