Description and classification of Indian Ocean humpback dolphin (Sousa plumbea) whistles recorded off the Sindhudurg coast of Maharashtra, India

Abstract

The Indian Ocean humpback dolphin (Sousa plumbea), a common cetacean species in India, has a diverse vocal repertoire, which to date has not been described in detail. This study focused on analyzing their whistle vocalizations. Humpback dolphins were recorded off the Sindhudurg coast of Maharashtra, India, and 2,260 whistles were analyzed for their acoustic characteristics. Whistles spanned a wide frequency range between 2.3 kHz and 33.0 kHz, with durations ranging from 0.01 s to 1.60 s. Whistles were categorized into seven contour classes based on their qualitative properties. A classification and regression tree (CART) analysis was used to quantify variability between the seven contour classes using the measured acoustic features. Based on the CART analysis, frequency gradient, minimum slope, maximum slope, beginning and ending slope accounted for most variability between whistle types. CART resulted in an overall classification accuracy of 89.5%. This study provides a detailed description of acoustic features and qualitative properties of humpback dolphin whistles from the northwestern coast of India. Further comparisons of acoustic data from Sousa populations along the Indian coast are necessary to determine possible geographic variations in whistle characteristics and whether the variations are driven by environmental or genetic factors or a combination of both.

Whistle characteristics of a newly recorded Indo‐Pacific humpback dolphin (Sousa chinensis) population in waters southwest of Hainan Island, China, differ from other humpback dolphin populations

“…However, the mean EF in Hainan was lower than that in the other Sousa species (Cochran‐Cox t ‐test, p < .05). We also found no significant difference for the mean FR between our study and other studies about S. plumbea (Bopardikar et al, 2018) and S. teuszii (Weir, 2010). The mean NoH in Hainan was higher than that reported in the other locations (Cochran‐Cox t ‐test, p < .05).…”

“…The descriptive statistics of whistle parameters for S. chinensis were compared with the same species recorded in Zhanjiang, China (Dong et al, 2019), Sanniang Bay, China (Z. Wang et al, 2013), Matang and Langkawi (Malaysia; Hoffman et al, 2015), as well as S. sahulensis in Australia (Berg Soto et al, 2014; Van Parijs & Corkeron, 2001), S. plumbea in India (Bopardikar et al, 2018) and Pakistan (Zbinden et al, 1977), and S. teuszii in Angola (Weir, 2010). Twelve variables were compared among S. chinensis studies, as shown in Table 4.…”

“…This can help to determine whether the 18 whistle parameters are different with the overall tonal classes. Descriptive statistics of whistle parameters were used (mean, SD , and whistle numbers) from previous publications (Berg et al, 2014; Bopardikar et al, 2018; Dong et al, 2019; Hoffman et al, 2015; Seekings et al, 2010; Van Parijs & Corkeron, 2001; Z. Wang et al, 2013; Weir, 2010; Zbinden et al, 1977). Based on the Levene's F ‐test result of the equality of variances, the two tailed t ‐test ( t ) for equal variances and Cochran‐Cox t ‐test ( t ') for unequal variances were used to test the differences between this study and the previous studies.…”

Spatio-temporal analysis identifies hotspots of marine mammal strandings along the Indian coastline: implications for developing a National Marine Mammal Stranding Response and Management policy

“…Maharashtra coast -Konkan Cetacean Research Team; for Indo-pacific humpback dolphins - (Sutaria and Jefferson 2004;Sutaria et al 2015;Bopardikar et al 2018;Jog et al 2018). This is likely to influence the proportion of strandings of that species which dominate the dataset, and patterns might not be generalised or even applicable to the whole group as considered in the study, due to differences in their biology and behaviour.…”

“…Sightings records on the east and west coast differ considerably due to differences in efforts undertaken to survey marine mammals. Maximum sighting reports were of dugongs obtained through dedicated interview surveys at its distribution sites followed by those of Indo-pacific humpback dolphins through the studies conducted on the west coast (Sutaria and Jefferson 2004;Sutaria et al 2015b;Bopardikar et al 2018). Hunting or capture data identified finless porpoise on the west coast (from the years 1827-1983) and dugongs on the east coast being hunted in the past as well as from records in the past ~100 years (records from 1910-2013).…”