Classification of Risso’s and Pacific white-sided dolphins using spectral properties of echolocation clicks

Abstract

The spectral and temporal properties of echolocation clicks and the use of clicks for species classification are investigated for five species of free-ranging dolphins found offshore of southern California: short-beaked common (Delphinus delphis), long-beaked common (D. capensis), Risso's (Grampus griseus), Pacific white-sided (Lagenorhynchus obliquidens), and bottlenose (Tursiops truncatus) dolphins. Spectral properties are compared among the five species and unique spectral peak and notch patterns are described for two species. The spectral peak mean values from Pacific white-sided dolphin clicks are 22.2, 26.6, 33.7, and 37.3 kHz and from Risso's dolphins are 22.4, 25.5, 30.5, and 38.8 kHz. The spectral notch mean values from Pacific white-sided dolphin clicks are 19.0, 24.5, and 29.7 kHz and from Risso's dolphins are 19.6, 27.7, and 35.9 kHz. Analysis of variance analyses indicate that spectral peaks and notches within the frequency band 24-35 kHz are distinct between the two species and exhibit low variation within each species. Post hoc tests divide Pacific white-sided dolphin recordings into two distinct subsets containing different click types, which are hypothesized to represent the different populations that occur within the region. Bottlenose and common dolphin clicks do not show consistent patterns of spectral peaks or notches within the frequency band examined (1-100 kHz).

Risso’s and Pacific white-sided dolphin habitat modeling from passive acoustic monitoring

“…Risso's dolphin habitat around the world is characterized by steep bathymetry and warm waters (Dohl et al 1983, Green et al 1992, Baumgartner 1997, Baumgartner et al 2001, whereas Pacific white-sided dolphin habitat is characterized by cool waters near the shelf-break (Benson et al 2002, Yen et al 2004, Becker 2007. Off southern California, Risso's dolphins produce one species-specific click type with distinct spectral patterns, while Pacific white-sided dolphins produce 2 spectrally distinct click types, denoted types PWS A and PWS B (Soldevilla et al 2008(Soldevilla et al , 2010a. Spatial and temporal trends in PWS A and PWS B click occurrence support the hypothesis that these click types respectively represent the morphologically and genetically distinct northern and southern populations that overlap in the SCB (Walker et al 1986, Lux et al 1997, Soldevilla et al 2010b.…”

“…Autonomous, fixed-sensor, passive acousticbased surveys offer a technique to assess dolphin occurrence over long periods, in remote locations, during adverse weather conditions and during nighttime periods. Recent spectral analysis of Risso's dolphin (Grampus griseus) and Pacific white-sided dolphin (Lagenorhynchus obliquidens) echolocation clicks off southern California revealed the existence of species and possibly sub-species click types (Soldevilla et al 2008) that can be used to examine their occurrence in autonomous acoustic data. Sampling delphinid echolocation clicks, which are produced most frequently during foraging activities (Norris et al 1994, BarrettLennard et al 1996, Van Parijs & Corkeron 2001, Nowacek 2005, also increases the likelihood that models represent prime foraging habitat.…”

Marine Mammal Demographics Off the Outer Washington Coast and Near Hawaii

“…Risso's dolphin echolocation clicks are broadband impulses with the majority of energy between 20 and 60 kHz ( Figure 21) and can be identified to species by their distinctive banding patterns observable in the LTSA, with energy peaks at 22, 26, 30, and 39 kHz (Soldevilla et al 2008). Acoustic detections of Risso's dolphins during this study occurred between August and March ( Figure 22) and they were detected more commonly than in previous years of monitoring in this area.…”

Lunar cycles affect common dolphin Delphinus delphis foraging in the Southern California Bight

“…LTSAs are similar to spectro grams, but each time bin contains an average of 500 non-overlapped Hann-windowed 10 ms frames whose spectra have been averaged with the algorithm from Welch (1967) resulting in 5 s time bins with 100 Hz re solution. Trained analysts manually screened 1 hour windows of LTSAs and identified acoustic encounters of echolocation in the HARP data while recording the presence of species-specific echo location signals of Pacific white-sided Lagenorhynchus obliquidens and Risso's Grampus griseus dolphins based on the click descriptions described in Soldevilla et al (2008) in order to exclude these species from this analysis. Acoustic encounters with Cuvier's Ziphius cavirostris and unidentified beaked whale species were classified according to the methods outlined in Baumann-Pickering et al (2013) and excluded from this analysis.…”

“…Individual echolocation signals were automatically detected using a computer algorithm with a 2-step ap proach (Soldevilla et al 2008, Roch et al 2011) and a minimum peak-to-peak received level threshold was set to 120 dB re: 1 µPa. This received level was defined based on a manual re view of the detection data to determine the received level at which echolocation clicks were no longer re liably detected.…”