Echolocation signals of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) in Sanniang Bay, China

Abstract

While the low-frequency communication sounds of Indo-Pacific humpback dolphins (Sousa chinensis) have been reported in a number of papers, the high-frequency echolocation signals of Sousa chinensis, especially those living in the wild, have been less studied. In the current study, echolocation signals of humpback dolphins were recorded in Sanniang Bay, Guangxi Province, China, using a cross-type hydrophone array with five elements. In total, 77 candidate on-axis clicks from 77 scans were selected for analysis. The results showed that the varied peak-to-peak source levels ranged from 177.1 to 207.3 dB, with an average of 187.7 dB re: 1 lPa. The mean peak frequency was 109.0 kHz with a À3-dB bandwidth of 50.3 kHz and 95% energy duration of 22 ls. The À3-dB bandwidth was much broader than the root mean square bandwidth and exhibited a bimodal distribution. The center frequency exhibited a positive relationship with the peak-to-peak source level. The clicks of the wild Indo-Pacific humpback dolphins were short-duration, broadband, ultrasonic pulses, similar to those produced by other whistling dolphins of similar body size. However, the click source levels of the Indo-Pacific humpback dolphin appear to be lower than those of other whistling dolphins.

Fine‐scale habitat use in Indo‐Pacific humpback dolphins, Sousa chinensis, may be more influenced by fish rather than vessels in the Pearl River Estuary, China

“…Identification of clicks and whistles were done by comparing the received signal with known vocalizations of S. chinensis within Chinese waters (Fang et al . , Wang et al . ).…”

“…Further to the detection ranges of the SoundTrap recorders, it is also important to note that marine mammal vocalizations analyzed were assumed to be from Indo-Pacific humpback dolphins. Identification of clicks and whistles were done by comparing the received signal with known vocalizations of S. chinensis within Chinese waters (Fang et al 2015, Wang et al 2016). Furthermore, the Indo-Pacific finless porpoise (Neophocaena phocaenoides) is the only other predominate marine mammal within the PRE and do not produce whistles but rather vocalize using predominately narrowband high frequency clicks (Goold and Jefferson 2002).…”

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…Clicks are very broadband with 10 dB bandwidths of 116±20 kHz, peaking at 114 kHz [241]. In China, a bimodal spectrum was found peaking at about 100 kHz and 180 kHz [249,250]. (Fig.…”

Echolocation click source parameters of Australian snubfin dolphins (Orcaella heinsohni)

“…The differences observed in biosonar parameters between these two studies may be due to species-specific differences; however, it is plausible that the different habitats and recording equipment could also contribute to explaining some of the observed differences. For example, a study by Fang et al (2015) reported lower source levels and shorter bandwidth for Indo-Pacific humpback dolphins in China compared to other dolphin species. The study, however, suffered from recording equipment limitations that likely gave rise to the reported differences.…”