ABSTRACT
Spectral parameters were used to discriminate between echolocation clicks produced by three dolphin species at Palmyra Atoll: melon-headed whales (Peponocephala electra), bottlenose dolphins (Tursiops truncatus) and Gray’s spinner dolphins (Stenella longirostris longirostris). Single species acoustic behavior during daytime observations was recorded with a towed hydrophone array sampling at 192 and 480 kHz. Additionally, an autonomous, bottom moored High-frequency Acoustic Recording Package (HARP) collected acoustic data with a sampling rate of 200 kHz. Melon-headed whale echolocation clicks had the lowest peak and center frequencies, spinner dolphins had the highest frequencies and bottlenose dolphins were nested in between these two species. Frequency differences were significant. Temporal parameters were not well suited for classification. Feature differences were enhanced by reducing variability within a set of single clicks by calculating mean spectra for groups of clicks. Median peak frequencies of averaged clicks (group size 50) of melon-headed whales ranged between 24.4 and 29.7 kHz, of bottlenose dolphins between 26.7 and 36.7 kHz, and of spinner dolphins between 33.8 and 36.0 kHz. Discriminant function analysis showed the ability to correctly discriminate between 93% of melon-headed whales, 75% of spinner dolphins and 54% of bottlenose dolphins.
ACKNOWLEDGMENTS
The authors thank Jeff Polovina and Dave Johnston (NOAA PIFSC), Frank Stone and Ernie Young (CNO N-45), and Curt Collins (NPGS) for support of this research. We thank Mark McDonald for his helpful critique of this manuscript. We also thank Xavier Alvarez Mico, Greg Campbell, Mandar Chitre, Chris Garsha, Megan McKenna, Nadia Rubio, Paul Seekings, Melissa Soldevilla, Charles Speed, Elizabeth Taylor, Yeo Kian Peen, for fieldwork, gear and analysis assistance. Successful field work was only possible due to the cooperative work of the staff of The Nature Conservancy, the Palmyra Atoll Research Consortium, and U.S. Fish and Wildlife Service. The research presented was funded by the NOAA Pacific Islands Fisheries Science Center, Chief of Naval Operation-N45, Naval Postgraduate School, and Scripps Institution of Oceanography, UCSD. Field work was conducted under USFWS SUP No. 12533 and NMFS Permit 727–1915.
