False killer whale and short-finned pilot whale acoustic identification

Citation:
Baumann-Pickering, S, Simonis AE, Oleson EM, Baird RW, Roch MA, Wiggins SM.  2015.  False killer whale and short-finned pilot whale acoustic identification. Endangered Species Research. 28:97-108.

Abstract:

False killer whales and short-finned pilot whales are known to interact with long-line fishing gear in Hawaiian waters, causing economic loss and leading to whale injuries and deaths. The main Hawaiian Islands insular population of false killer whales is listed as endangered and the offshore population is considered “strategic” under the Marine Mammal Protection Act due to relatively high bycatch levels. Discriminating between these species acoustically is problematic due to similarity in the spectral content of their echolocation clicks. We use passive acoustic monitoring along with data from satellite tags to distinguish signals from these two species. Acoustic encounters recorded with autonomous instruments offshore of the islands of Hawai‘i and Kaua‘i were matched with concurrent and nearby location information from satellite tagged individuals. Two patterns of echolocation clicks were established for the two species. The overall spectral click parameters were highly similar (22 kHz peak and 25 kHz center frequency), but false killer whales had shorter duration and broader bandwidth clicks than short-finned pilot whales (225 μs, 8 kHz (-3 dB bandwidth) and 545 μs, 4 kHz, respectively). Also, short-finned pilot whale clicks showed distinct spectral peaks at 12 and 18 kHz. Automated classification techniques using Gaussian mixture models had a 6.5% median error rate. Based on these findings for echolcoation clicks and prior published work on whistle classification, acoustic encounters of false killer whales and short-finned pilot whales on autonomous instruments should be identifiable to species level, leading to better long-term monitoring with the goal of mitigating bycatch.

DOI:

10.3354/esr00685