How does anthropogenic (human-generated) sound affect marine animals? The ocean is full of both natural and anthropogenic sources of sound (see What are common underwater sounds?. Much attention has recently been focused on anthropogenic sources of sound in the ocean and their potentially harmful effects on marine animals. This has become a topic of increasing controversy, especially regarding marine mammals.

Marine mammals face threats from many different human activities, including fishing, habitat destruction, ship strikes, whaling, and sound production. Of these threats, fisheries bycatch kills the most marine mammals. Globally, it is estimated that more than 650,000 marine mammals are killed annually by being accidentally caught in fishing nets ^[1]. Although there have only been a small number of deaths of marine mammals associated with underwater sound, sound is included here as a threat because we know that it can affect marine mammals in a number of ways.

Researchers ^{[2] [3]} suggest that increased background noise and specific sound sources might impact marine animals in several ways. The potential impacts include sounds that cause marine animals to alter their behavior, prevent marine animals from hearing important sounds (masking), cause hearing loss (temporary or permanent), or damage tissue. In at least a few well-documented cases there is a relationship between the use of mid-frequency sonar and the stranding of cetaceans, particularly beaked whales.

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
• Strandings