Regional bathymetric map of the study site offshore of southern California. The 14 × 14 km box is the monitoring site northwest of San Clemente Island (SCI) and southwest of Santa Catalina Island (CAT) on the ridge between the eastern Santa Catalina Basin and the southwestern San Nicolas Basin. R/P FLIP is centered 1000 m from the four small black circles, 800 m deep HARPs (Table I ). The thick contour is 1000 m deep, thethin contour is the coastline, and darker shading is deeper. Box shows location of Figs. 5 and 6 .
Hourly dolphin acoustic behavior over one month from spectrogram evaluation of the northern HARP. Shaded light gray period from 0200 to 1300 is nighttime. Black indicates mostly whistling, dark gray is whistling-clicking, and medium gray is mostly clicking behavior. Whistling is predominately during daytime hours, whereas, mostly clicking increases and whistling-clicking decreases throughout the night until daybreak.
LTSA of a bout of dolphin acoustic activity (∼3 h). The long duration spectrogram starts at 1200 GMT and shows mostly clicking (25 kHz–100 kHz) activity with some whistling (10 kHz–15 kHz). At morning civil twilight (1400 GMT), the acoustic behavior changes to intense mostly whistling (7 kHz–20 kHz).
Wideband (10 kHz–100 kHz), one-hour LTSAs (left panels) and four-second, narrowband (5 kHz–20 kHz) spectrograms (right panels) from four concurrent nighttime HARP recordings. The dolphins appear to be heading mostly toward the west instrument with some directed toward the north and to a lesser extent to the south recorder. The spectrograms of whistles are from about 02:15 GMT. LTSA and spectrogram gains, including hydrophone sensitivities, are the same across recordings. LTSAs were calculated with a Hanning window, 2000-sample DFT and 5 s spectral averages. Spectrograms were calculated with a Hanning window, 20 000-sample DFT and 50% overlap.
Map view of 70-min daytime dolphin track from 575 whistle localizations. Filled circles are dolphin whistle locations with shading corresponding to the time scale bar at the right. HARP and R/P FLIP locations are squares and triangle, respectively, occupying a ridge between two basins. Visual observations from R/P FLIP of Delphinus sp. are depicted as diamonds and are labeled with sighting time. The thick contour lines are 1000 m deep with thin lines at 50 m increments.
Map view of 2-h nighttime dolphin positions from 325 whistle localizations. Filled circles are dolphin whistle locations with shading corresponding to the time scale bar at the right. HARP and R/P FLIP locations are squares and triangle, respectively, occupying a ridge between two basins. The thick contour lines are 1000 m deep with thin lines at 50 m increments.
Array positions from acoustic-GPS localization (±5 m rms).
Article metrics loading...
Full text loading...