Sound in many ways is the lifeblood of marine animals. It connects them, and offers them a sensory window to the surrounding world much like light does for land animals, like us. The ocean is dark, vast, and continually mixed, which favors the acoustic channel as the primary mode of communication and detecting key information over any appreciable distance. All marine vertebrates appear to rely heavily on sound for many key aspects of their lives, such as social interaction, feeding, avoiding predators, and finding their way around. The sounds they make and how they detect them are as varied as the species themselves, but sound production and reception are vitally important across many ocean taxa.

The ocean has long been a cacophonous acoustic scene, with natural sources ranging from waves, wind, and rain to biological sources to earthquakes and lighting strikes. Many ocean animals have evolved fascinating ways to live and utilize this sea of sound. For some marine mammals, such as sea otters, there are key events and acoustic cues both in air and underwater; these different media present very different challenges and evolutionary approaches to amphibious sound communication.

Recently, humans have begun to introduce various sounds into the marine environment. Some of these sounds are loud but typically relatively brief or mobile, like seismic exploration for oil and gas, active sonar systems, or impulsive noise associated with marine construction or explosions. Others are less acute and dramatic but may be more perniciously omnipresent in their spatial and temporal scale, such as the tens of thousands of large commercial ships putting increasing volumes of low frequency noise into the ocean. For various interested groups, from industry to the military and from the regulators to environmental groups, the relative effects of these kinds of sounds has been an area of increasing interest and investigation. The potential for direct harm or behavioral harassment from these different sources remains generally poorly understood, but new tools and technologies are providing some insights.

For instance, the responses of marine mammals to active sonar systems is being studied in different places around the world, including right off the California coastline. A project entitled the Southern California Behavioral Response Study (SOCAL-BRS) is providing basic behavioral data on a wide range of marine mammal species and direct measurements of their responses to sound exposure in a controlled way. Basically, researchers track animals for a fairly short period using extremely high-resolution movement and acoustic sensors and then test their responses to controlled levels and types of sound using specific safety protocols. Sea otters or pinnipeds have not yet been part of this project, but nearly a dozen cetacean species have been. The results are emerging from the first few years, strongly suggesting that species type and the relative context of sound exposure may be as or more important to determining the probability of response as the simple approach of measuring how loud it is that has been the level of sophistication in the regulatory approach to date.

Current and pressing issues regarding marine mammals and sound are occurring off our shores all the time. These include the more dramatic but limited scale acute events like a sonar event or a seismic airgun study. But they also include changes in the baseline, long-term acoustic ecology of the ocean from chronic sources like those associated with commercial ships. More information on some of these issues is available on: – Discovery of Sound in the Sea