Marine mammal tracks from two-hydrophone acoustic recordings made with a glider

Abstract

Abstract. A multinational oceanographic and acoustic sea experiment was carried out in the summer of 2014 off the western coast of the island of Sardinia, Mediterranean Sea. During this experiment, an underwater glider fitted with two hydrophones was evaluated as a potential tool for marine mammal population density estimation studies. An acoustic recording system was also tested, comprising an inexpensive, off-the-shelf digital recorder installed inside the glider. Detection and classification of sounds produced by whales and dolphins, and sometimes tracking and localization, are inherent components of population density estimation from passive acoustics recordings. In this work we discuss the equipment used as well as analysis of the data obtained, including detection and estimation of bearing angles. A human analyst identified the presence of sperm whale (Physeter macrocephalus) regular clicks as well as dolphin clicks and whistles. Cross-correlating clicks recorded on both data channels allowed for the estimation of the direction (bearing) of clicks, and realization of animal tracks. Insights from this bearing tracking analysis can aid in population density estimation studies by providing further information (bearings), which can improve estimates.

A Response to Scientific and Societal Needs for Marine Biological Observations

“…There are many exciting technologies under development that lend themselves to routine, operational monitoring of marine populations and habitats, including improved platforms, sensors, data analysis and processing. For example, passive acoustics has been used to monitor the presence and movement patterns of species that vocalize (Hildebrand et al, 2015;MacIntyre et al, 2015;Širovic et al, 2015;Munger et al, 2016;Kusel et al, 2017). Satellite images have been used to locate seabird and seal colonies and assess their population numbers (LaRue et al, 2011;Trathan et al, 2011;Fretwell et al, 2012Fretwell et al, , 2014Fretwell et al, , 2015Fretwell et al, , 2017LaRue et al, 2017), whales at sea (Cubaynes et al, 2018), plankton functional groups and structured benthic habitats (Muller-Karger et al, 2018a).…”

High-resolution observations in the western Mediterranean Sea: the REP14-MED experiment

“…New payloads for gliders were tested during the experiment: glider Clyde was equipped with two hydrophones and an experimental pH/p(CO 2 ) sensor was for the first time installed on glider Fin. Although Clyde failed about 36 h after its deployment, the acoustic records were intact and complete because they were anyway limited to approximately 23 h. The equipment used and the analysis of the data obtained are discussed by Küsel et al (2017). Sperm whale regular clicks as well as dolphin clicks and whistles were identified.…”

The Use of Underwater Gliders as Acoustic Sensing Platforms

“…Due to the advantages in terms of self-noise and duration, as well as the flexibility for acoustic payload installation [5,6], gliders are considered to have great potential in ocean acoustics applications, for example, studying whales [7,8] and fish sounds [9], acoustic sources detection and tracking [10][11][12], and measuring the marine soundscape [13]. In [8], a real-time passive acoustic monitoring device was developed and installed in the glider, which detected and classified 14 types of calls from four species of baleen whales.…”

“…In addition to target detection, those gliders can estimate the target azimuth to a certain degree. In [10], an underwater glider mounted with two hydrophones was deployed for studying marine mammal population density. The glider's recording system could detect and classify the sounds from different mammals, and sometimes even track and locate them.…”

“…The signal DOAs are estimated through the time difference of arrival (TDOA) method [10,12]. The TDOA ∆T is estimated by calculating the cross-correlation between two SCHs.…”