Abstract
This study presents an integrative bioacoustics approach to discriminate eight species of odontocetes found on the outer continental shelf and slope of the western South Atlantic Ocean. Spinner, Atlantic spotted, rough-toothed, Risso’s, bottlenose, short-beaked common dolphins, killer and long-finned pilot whales were visually confirmed during recordings with a 3-element omnidirectional hydrophone array. Spectral and time parameters of whistles and echolocation clicks were used in a discriminant function analysis and a classification tree model. As a first step, whistles and clicks were analysed separately; a further analysis consisted of both vocalisations jointly classified. All species showed species-specific properties in their vocalisations. Whistles had greater misclassification rates when compared to clicks. The correct classification was enhanced by the joint step, given the 5.8% error in the discriminant function analysis and a misclassification rate of 18.8% in the tree model. In addition, Receiver Operating Characteristic curves resulting from the tree algorithm analysis exhibited better model efficiency for all species in the joint classification. These findings on acoustical discrimination of such abundant and cosmopolitan species contribute to delphinid classification systems.
Highlights
This study proposes an integrative bioacoustics approach using whistles and clicks to discriminate the following eight delphinid species: spinner (Stenella longirostris), Atlantic spotted (S. frontalis), rough-toothed (Steno bredanensis), Risso’s (Grampus griseus), bottlenose (Tursiops truncatus), short-beaked common (Delphinus delphis) dolphins, killer (Orcinus orca) and long-finned pilot (Globicephala melas) whales which are found on the Brazilian outer continental shelf and slope of the western South Atlantic Ocean
Differences among acoustic parameters of whistles and clicks of delphinid species When tested for differences with a Kruskal-Wallis test, all parameters for clicks and whistles showed significant results (p
Atlantic spotted dolphins had the highest values for maximum frequency, delta frequency, peak frequency, centre frequency and ending frequency, while spinner dolphins had the highest median values for minimum frequency and inter-click interval
Summary
Odontocetes species commonly emit tonal frequency-modulated whistles and broadband pulsed clicks and burst sounds [1], and the production patterns of these acoustic signals vary with geographic location, behavioural state, and geometric spacing of conspecifics [2,3,4]. Some progress has been made in discriminating delphinid whistles to species [5,6,7,8] and with respect to clicks for porpoises, sperm whales, beaked whales and dolphins [9,10,11,12,13]. The funders had no role in this study design, data collection and analysis, decision to publish, or preparation of the manuscript
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