New passive acoustics tools help identify fish sounds in the wild

Close-up of a lingcod fish underwater
Using his passive acoustic tools, Mouy was able to capture the sounds of the lingcod for the first time. Photo credit: Xavier Mouy

The ocean is not a quiet place. While many people are aware of the melodic sounds produced by whales and dolphins, they may not realize that many fish also make sounds. Fish may be moving their bones, grinding their teeth, releasing air bubbles or making their swim bladder vibrate to communicate information about their food, their territory, or reproduction. However, despite the fact that fish are the largest and most diverse group of sound-producing vertebrates in the ocean, there is still much we don’t know about the distinct vocal repertoire of the various fish species.

Xavier Mouy, a recent UVic PhD graduate co-supervised by Stan Dosso and Francis Juanes, aims to change that. In a recent study published in Methods in Ecology and Evolution, Mouy and his collaborators describe a set of new passive acoustic tools that can be used to non-intrusively study fish sounds in the wild.

“Fish sounds could be incredibly useful for monitoring the presence and behavior of fish species in the environment, but at the moment, we often can’t identify which species are producing the sounds we record. We need methods to identify and catalogue the sounds that each fish species produces.”

- Xavier Mouy, UVic PhD graduate in Earth and Ocean Sciences.

The most common method to identify fish sounds involves placing fish in a contained environment, such as a tank, and recording them. However, this approach is far from ideal, as many fish don’t vocalise in captivity. Even if they do, the sounds can be so distorted by the reflections on the tank’s walls that what is recorded is not representative of what would be recorded in the wild.

Mouy wanted to develop a tool to identify fish sounds that could be used in the fishes’ natural environment and could record sound autonomously for up to two weeks. The result was three different portable audio-video platforms: a large array, a mini array and a mobile array. All three use several hydrophones to localize fish sounds in three dimensions, and video cameras to identify the species and behavior of the localized fish. Two of these platforms are static and are deployed on the seafloor to study specific sites, while one uses an underwater drone to actively search for fish.

“Each array is purpose-built for a different scenario: the large array will give the most accurate 3D acoustic localization, the mini array is best for deploying on rough or uneven seafloors, and the mobile array allows for real-time positioning in response to observed fish presence. Having three different arrays allows us to study a wide variety of fish habitats, as we can choose the best option for each situation” says Mouy.

Illustration comparing the three different arrays
Comparison of the three audiovisual arrays. Credit: Xavier Mouy

Mouy has proven that all three arrays can identify species-specific fish sounds in the wild. He deployed the arrays in four different locations around Vancouver Island and identified sounds from three fish species that have never been found to produce sound before: the quillback rockfish (listed as a threatened species by the Committee on the Status of Endangered Wildlife in Canada), copper rockfish, and lingcod. These sounds will soon be added to the Fish Sounds Project database.

Mouy hopes his new set of tools can be useful not only for identifying new fish sounds, but also for monitoring.

“Currently, there are 164 rockfish conservation areas established in British Columbia. The goal is to help protect fish species whose survival may be threatened. However, there’s no efficient way to monitor the fish populations in many of these areas, so it’s difficult to know if these areas are effective,” says Mouy.

Passive acoustics has a high potential to improve the monitoring and management of these important fish species and Mouy’s work is an important contribution that will help make this happen. Mouy hopes that future research will not only be able to identify the presence of specific fish species but also determine how many fish are present. This is expected to be much more efficient and effective than the costly and infrequent diver-based surveys that are currently used to monitor fish populations.

As part of his recently published paper, Identification of fish sounds in the wild using a set of portable audio-video arrays, Mouy has published all the building instructions for his arrays and made all related materials and processing software open source. He hopes that other researchers will use this work to identify additional fish sounds around the world, implement monitoring strategies and further this research.

The publication of this paper brings Mouy’s PhD work to a close. He graduated with his PhD in Earth and Ocean Sciences in spring 2022 and is now a post-doctoral fellow with the passive acoustics group at the North East Fisheries Science Centre, a branch of NOAA Fisheries.

Mouy’s work was supported by the Canadian Healthy Oceans Network, the Natural Sciences and Engineering Research Council, the Liber Ero Foundation and CFI/CBKDF funding.