Communication
How Sound is Made
Whales are highly social creatures who utilize sounds like whistles, chirps, clicks, and songs to communicate with one another. Baleen whales utilize their larynx to make these sounds. Within the larynx there is a thick fold of u-shaped tissue that is known as the u-fold. It is next to the laryngeal sac which inflates when muscles in the throat and chest contract, causing airflow between the sac and the lungs. Sound is produced when the expansion and contraction of the laryngeal sac and lungs push air across the u-fold, causing it to vibrate. Different levels of laryngeal sac inflation can change the frequency of the sound that is produced. Toothed whales are also known to produce sound by opening and forcefully closing their jaws underwater, known as jaw claps, which usually signals aggression. (Yamato, et al 2012) Blue whales are the loudest animals on the planet, reaching 180 decibels.
Hearing
Acoustic impedance does not occur in the sea due to the fact that water is denser than air. This means that unlike terrestrial animals where sound enters at angle, sound travels into the ear in a straight line for marine animals. In the water sound waves keep a lot of their momentum, these fast powerful sound waves cause acoustic interference, which makes it difficult to locate where the sound is coming from. In order to counteract this, the middle ear has evolved to be outside of the skull. Whales have a bony bulbous structure called the tympanic bulla to house the tympanic membrane, or ear drum, and ossicles, or ear bones. Toothed whales have an adaptation that allows them to feel the sound waves in their lower jaw and transmit the vibration information to their ear. (Ketten 2002)
Temperature and Pressure Effect Sound Waves
Temperature and pressure determine the distance and speed that sound can travel through water. Sound made close to the surface of the ocean will not travel very far as there tends to be a lot of wave movement and the waves easily become scattered. When sound travels through the depths, the distance it can travel increases and the speed begins to decrease. As the temperature drops and the pressure increases, the sound waves refract downward. Once the thermocline layer is reached the sound waves will be traveling at their minimum speed. In this region temperature and pressure quickly change. The temperature reaches its coldest levels and remains constant while the pressure continues to increase. Here the speed of the sound waves begins to increase and are refracted upwards. This is known as the sound channel, where sound waves can travel thousands of kilometers without losing much momentum, allowing low frequency sound waves produced by baleen whales to travel thousands of kilometers.(Lee 2021)
Whale Culture
Humpback whale songs have been studied by researchers over the span of about 13 years. They found that whales within the same population will sing the same songs. These songs are complicated and filled with different kinds of noises and repeated patterns of sound, like a chorus found in human songs. Over time the songs that these whales sing changes, and all the males learn the new version. When different whale populations encounter one another during migration or feeding their songs tend to evolve and spread to different parts of the ocean. Due to these exchanges and evolution of songs learned by different populations, whales are said to have culture, something that used to be thought of as exclusively human. (Morell 2018)