Automatic Detectors for Underwater Soundscape Measurements

Environmental impact regulations require that marine industrial operators quantify their contribution to underwater noise scenes. Automation of such assessments becomes feasible with the successful categorisation of sounds into broader classes based on source types – biological, anthropogenic and physical. Previous approaches to passive acoustic monitoring have mostly been limited to a few specific sources of interest. In this study, source-independent signal detectors are developed and a framework is presented for the automatic categorisation of underwater sounds into the aforementioned classes

Humpback whale singing activity off the Goan coast in the Eastern Arabian Sea

<p>For over two decades, passive acoustic monitoring (PAM) methods have been successfully employed around the world for studying aquatic megafauna. PAM-driven studies in Indian waters have so far been relatively very scarce. Furthermore, cetacean populations inhabiting the north western Indian Ocean are far less studied than those in many other regions around the world. This work likely constitutes the first systematic study of the vocal repertoire of humpback whales (<i>Megaptera novaeangliae</i>) at a near-shore site along the western coast of India. Analysis of the observed vocalizations provides an insight into the behaviour of the species. This is significant as it assists in developing a better understanding of the habitat use of the non-migratory Arabian Sea humpback whale population. In contrast, other breeding populations such as those around the North Atlantic, South Pacific and Australia have been relatively well studied. Underwater passive acoustic data were collected during March 2017 using an autonomous logger at a shallow-water site off the eastern edge of Grande Island off the coast of Goa. Humpback whale vocalizations were found to occur over multiple days in the recordings. Time–frequency contours of individual units of vocalization were extracted with the aid of an automatic detection technique and the characteristics of the units were measured. Further, successive units were analysed for formation of phrases and themes. Reconstruction of putative songs from the identified units and themes was not possible due to the limitations imposed by the nature of data collection. Detailed analyses of units, phrases and themes are presented.</p

The underwater soundscape around Australia

The Australian marine soundscape exhibits a diversity of sounds, which can be grouped into biophony, geophony and anthrophony based on their sources. Animals from tiny shrimp, to lobsters, fish and seals, to the largest animals on Earth, blue whales, contribute to the Australian marine biophony. Wind, rain, surf, Antarctic ice break-up and marine earthquakes make up the geophony. Ship traffic, mineral and petroleum exploration and production, construction, defence exercises and commercial fishing add to the anthrophony. While underwater recorders have become affordable mainstream equipment, precise sound recording and analysis remain an art. Australia’s Integrated Marine Observing System (IMOS) consists of a network of oceanographic and remote sensors, including passive acoustic listening stations managed by the Centre for Marine Science & Technology, Curtin University, Perth. All of the acoustic recordings are freely available online. Long-term records up to a decade exist at some sites. The recordings provide an exciting window into the underwater world. We present examples of soundscapes from around Australia and discuss various aspects of soundscape recording, analysis and reporting—the to-dos and not-to-dos