Fish and invertebrates produce sounds that help them obtain food, avoid predators, and communicate. Fish typically make sounds as a part of their courtship rituals during spawning. Many of these low-frequency knocks, grunts, and drumming sounds can be used to identify animals by species or group. Invertebrates produce various rumbles, creaks, and snaps. These sounds can be a byproduct of their feeding behavior or intentionally produced to stun their prey or deter predators.

We use non-invasive passive acoustic monitoring to study the sounds produced by fish and invertebrates. We deploy hydrophones at sea and analyze the sounds we record to help us answer a range of questions about these species:

• Which species are present?
• What kind of sounds do they make and why?
• What other sounds are they exposed to?
• Where and when are they spawning and may need protection?

Sound Identification

Part of our work involves listening to different fish and invertebrate sounds and identifying them by species. Some sounds indicate specific behaviors such as feeding or spawning. For example, male haddock will make knocking sounds to attract mates during their spawning season. They create these knocks by contracting specialized muscles against their swim bladder. Snapping shrimp make loud snapping sounds to stun their prey or deter predators. They have two claws, one of which is enlarged. These shrimp can open and close the larger claw so rapidly that a bubble forms and pops (a process called cavitation), creating a loud snap.

We can process our data using acoustic detectors which help us find sounds made by certain species in our recordings. Scientists then analyze the detected sounds in a spectrogram—a visual display of the sound—and identify which species are present and what they might be doing. When many individuals in a fish or invertebrate population are creating noise simultaneously, the noise level can impact the ocean soundscape. The ocean soundscape is all of the sources that contribute sound to the environment, including biological, environmental, and human-made. They can even interfere in research if they are masking sounds made by other species we want to study.

Noise Exposure

Sounds made by human activity contribute significantly to ambient ocean noise levels. The noise type and level can affect the ability of fish and invertebrates to communicate underwater and limit our ability to hear them in our passive acoustic data.

Most fish produce low-frequency sounds which overlap with the frequency of sounds produced by vessels, airguns towed behind ships for seismic surveys, pile driving for construction, and echosounders. Some invertebrates, such as snapping shrimp, can produce higher frequency sounds. Their sounds span all of the frequency ranges of sounds caused by humans, including echosounders and high-resolution geophysical equipment used to survey sites for offshore wind energy. These human-caused sounds can harm fish and invertebrates by making it difficult for these animals to hear each other. We work to ensure that human activities avoid and minimize impacts to these animals.

We conduct a range of ocean noise research projects with our collaborators to monitor these human-caused noise levels and how they may be affecting the habitats, behavior, and health of marine mammals.

Spawning Behavior and Conservation

Many fish and marine invertebrate species gather together during their spawning seasons to increase the likelihood of successful reproduction. If environmental conditions are suitable, populations may return to the same spawning site year after year. Understanding where spawning sites are located and when different species are using them is critical for species conservation. Using passive acoustic monitoring to record, detect, and classify sounds by species allows us to learn more about when and how they are using certain areas.

We deploy hydrophones to listen in critical habitats and areas with increasing human activity. We monitor for several fish and invertebrate species, including Atlantic cod which make a characteristic grunting sound during their spawning season. The population has been in decline due to multiple factors, including overfishing. We deploy ocean gliders and bottom-mounted recorders to detect their grunts and identify potential spawning sites. These analyses can be used to assess potential threats to populations. For example, if the underwater construction of wind turbines or installation of underground cables in an offshore wind energy development area overlaps with a spawning site, it could disrupt the fish's spawning activities and lead to further population decline.