Analysis Of Underwater Vocalizations Types And Characteristics Of Dugongs,Indo-Pacific Humpback Dolphins,and Weddell Seals

Sound plays an important role in the life of Marine mammals.Based on the underwater vocalization of dugongs,Indo-Pacific humpback dolphins,and Weddell seals,voice signals were detected and identified.The signals of three marine mammals were classified by manual inspection and multivariate analysis,and the characteristics of each type of sound signal were analyzed statistically by extracting signal characteristic parameters.The main conclusions were as follows:The vocalization of wild dugong in Thai waters can be divided into four types:chirp,trill,bark,and whistle.Chirps,trills,and whistles were all frequency modulation signals with harmonic structure,and the fundamental frequency range was mainly in the range of 2-5 k Hz.The main differences were in duration and number of inflection points.Trills had the longest duration and the largest number of inflection points.Chirps had the shortest duration and the least number of inflection points.Whistles fell somewhere in between.Barks were broadband and non-frequency modulation signals with a duration of about 0.20 s and a bandwidth range of 0.2-4.0 k Hz with the frequency concentrated below 4.0 k Hz.The proportions of these four types of acoustic signals were different,among which chirps accounted for more than 86%,trills and whistles accounted for about 7% and 6% respectively,while bark accounted for less than 1%.The acoustic signals of wild Indo-Pacific humpback dolphins in Beibu Gulf can be divided into two categories: whistles and pulsed signals.Whistles can be further divided into seven types: constant,upsweep,downsweep,convex,concave,sinusoidal,and step whistles.Whistles emitted by Indo-Pacific humpback dolphins were mainly in the range of 5-10 k Hz,and the duration of most whistles was less than 1 s.The pulsed signals of Indo-Pacific humpback dolphins can be divided into three categories: clicks,burst-pulses,and buzzes.These three types were all shown as a series of high-frequency pulses,but the main difference lay in the different inter-pulse intervals(IPI).Clicks had the highest IPI,followed by burst-pulses,and buzzes had the lowest.The results showed that clicks were the most frequently used in almost all behaviors of Indo-Pacific humpback dolphins,and were mainly used for navigation and positioning.Burst-pulses were related to the surface behavior,which were mainly used to communicate between groups.Buzzes were found mainly in foraging behavior,but also social interactions.The vocal signal repertoire of Weddell seals obtained from Zhongshan Station in Antarctica was numerous and the signal types were complex,which can be divided into two categories: frequency modulation signal and pulsed signal.The frequency range of these two types was large,ranging from several hundred Hertz to tens of kilohertz,and both contain single or multiple elements with different time and frequency patterns.Signals with a single element were usually longer in duration,while signals with a shorter duration(<1 s)were mostly composed of multiple elements.