Marine fishes face threats from many different human activities, including overfishing, habitat degradation and loss, bycatch, and sound production. Commercially exploited fish populations have experienced population declines of 83% over the past 2–3 decades ^[1]. Although much of the attention on the effects of anthropogenic (human-generated) sounds on marine animals has focused on marine mammals, the same concerns are being raised about the effects of sound on fishes. Fishes and marine mammals both have ears containing sensory hair cells, which suggests that similar effects may be expected in the two groups. However, much less is currently known about the effects of underwater sound on fishes than on marine mammals.

Coral reefs are especially noisy due to high densities of shrimps, urchins, fishes, and other organisms. Image credit: NOAA.

There are many types of marine habitats, such as nearshore, offshore, and deep ocean, each with a different soundscape. We know very little about the sound characteristics of some habitats. One habitat that has been fairly well studied is coral reefs. These are noisy environments because of abundant naturally produced sounds like winds, waves, and sounds produced by a large number of inhabitants (for more information see What are common underwater sounds?). An understanding of the natural soundscape is needed to determine the impact of sounds contributed by human activities.

Sources of anthropogenic sound are extensive and include commercial and recreational boats, large ships, seismic exploration devices (such as airguns), construction activities (such as pile driving), and active sonar (used by the by the shipping industry, commercial and recreational fisheries, the military, and the oceanographic research community). Potential effects on fish from intense anthropogenic sounds, such as those associated with airguns and pile driving, could include: death, tissue damage, or injuries that might not directly result in death but may make a fish more vulnerable until healing takes place; temporary hearing loss; behavioral changes, such as moving towards or away from a sound source; and increased stress. There is also the potential for these sounds to have no effect on fish, especially if the level of the sound received by the fish at a distance from the source is not great. Longer lasting sounds, such as those associated with shipping, cause a general increase in background noise in some locations. Based on the way the ear works in fishes, this increase in background noise may result in the masking of biologically important sounds that are critical for fish behavior. It is far more difficult for a fish to escape from general increases in background noise as opposed to brief and/or localized sounds that are often moving (e.g. sonar) or that fish may swim by (e.g. pile driving) ^[2]. These effects require more research, although masking by background sound has been measured in several studies.

A number of factors affect the impact of sounds on marine animals. These include the sound level, its frequency, and other characteristics of the sound; the hearing sensitivity, age, sex, and behavior of the animals; and the environmental conditions under which the animals experience the sound.

It is difficult and expensive to study marine animals. Although there is little doubt that increases in underwater sound are likely to affect fish, much more research on a diversity of fish species and different sound sources is necessary in order to fully understand the extent of these effects. The effect of sound on different life history stages of fish and the relative effects of sound on different species also need to be considered. Fish eggs that are stationary in nests, for example, could be exposed to sound that may affect development and survival ^[3]. Studies on the behavioral responses of fish to anthropogenic sound also need to be conducted in their natural habitats in order to understand “wild” responses of fish to human-generated sound.

There are >31,000 species of living fishes (www.fishbase.org). Most of these are marine fishes. However, experimental work on the effects of sounds on fish has been carried out on freshwater fishes because they are more accessible. The structural, physiological, and behavioral similarities among all fishes allows freshwater fishes to serve as appropriate proxies for marine fishes in the context of scientific investigations.

The following sections discuss effects that have been discovered using rigorous scientific methods and are published in the scientific literature.

• Behavioral Changes
• Masking
• Hearing Loss
• Physiological Stress