How do whales and dolphins use sound to communicate underwater?

Many cetaceans rely heavily on sound because sound travels much faster and farther in water than light does. Dolphins use whistles for social communication and clicks for echolocation, while baleen whales such as humpbacks produce long, complex songs that can last for hours. Some whale calls can travel hundreds of kilometers under the right ocean conditions. Scientists have recorded sperm whales using patterned click sequences known as codas, which appear to carry social information. Human-made noise from ships and sonar can interfere with these calls and make communication harder.