Map of study area including locations of HARP deployments. Depths are indicated by colorbar. Sites: Conception, Barbara Channel, Basin, Nicholas Basin, Clemente Island, and Catalina Island. HARP locations are presented as pie charts in which the black area indicates the percentage of recording days with Risso’s dolphin click bouts present. Risso’s dolphins were detected most often at CAT and least often at TB and SNB.
Schematic representation of autonomous seafloor recording package.
Example LTSA illustrating echolocation click bout containing the unique spectral peak and notch structure described for Risso’s dolphins by Soldevilla et al. (2008) . LTSA spectrogram has resolutions of 100 Hz and 5 s in frequency and time, respectively, and represents coherent averages of 500 spectra created using 2000-point, 0%-overlapped, Hann-windowed HARP data. Spectral peaks occur in the Risso’s dolphin clicks at approximately 22, 25, 31, and 39 kHz.
Diel pattern of Risso’s dolphin echolocation click bouts combined across the six HARP locations. Vertical bars represent the percentage of days that have clicks present in each 1 h time bin. Horizontal bar indicates periods of light (white) or darkness (dark gray). Light gray areas represent periods that may be light or dark depending on time of year.
Variation in Risso’s dolphin click bout occurrence (a) and daily mean-adjusted click rate (b) between day and night periods. Central lines represent median value, boxes contain 25th to 75th percentiles, and whiskers contain 5th to 95th percentiles of data. Click bout occurrence and daily click rate anomaly are both significantly higher during the night than during the day.
Seasonal and annual variation in mean days per week with Risso’s dolphin click bouts at the six HARP sites. Bar colors indicate year: , light , and dark . Error bars indicate standard deviation. Black dots indicate no data available in that season and year. Sites: Conception, Barbara Channel, Basin, Nicholas Basin, Clemente Island, and Catalina Island.
Seasonal recording effort at each site across 3 years of study. Cells represent the number of week-long replicate samples available for statistical analysis at each site for each season of each year. Site abbreviations: Conception, Barbara Channel, Basin, Nicholas Basin, Clemente Island, and Catalina Island. TB and SNB are not included in the total samples for the seasonal analysis in this study because they were deployed during only part of the year in 2007 and did not sample across all seasons. Months included in each season are indicated by the first letter of the month.
Summary of number of days and hours with recording effort, number of days and hours with Risso’s dolphin click bouts present, percentage of days and hours with Risso’s click bouts present, and mean instrument depth for each of the six HARP sites. Site abbreviations: Conception, Barbara Channel, Basin, Nicholas Basin, Clemente Island, and Catalina Island.
Results of three-way ANOVA for seasonal, annual, and site effects on Risso’s dolphin occurrence. The main effects of season and site, and the interaction effects of , , and all significantly influenced the occurrence of Risso’s dolphin click bouts.
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