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Sperm whales click, both to communicate with other sperm whales (‘coda’ sequences), and to investigate objects and hunt prey (‘click trains’ and ‘creaks’). Their clicks are some of the most powerful sounds produced by any animal and in quiet conditions, can be hear over
distances of 10 km or more. Sperm whales generally inhabit very deep oceanic waters where they dive several hundreds of metres depth for periods of 30-45 min. Females and young sperm whales inhabit tropical and sub-tropical waters, but males make long migrations into temperate and colder regions feed.
The vocalisations of bottlenose dolphins include echolocation click trains a form of biological sonar, which they use to navigate and investigate objects in the marine environment, and to hunt for prey. The also make a wide range of communication sounds: pulsed calls (e.g. ‘squawks’, ‘barks’, ‘raspberries’ and ‘buzzes’) and whistles. Whistles are believed to carry information about the identity of the caller (‘signature whistles’).
Short-beaked Common Dolphin
Common dolphins, like other dolphin species, produce echolocation click trains to navigate and examine their immediate surroundings. Much of the energy of their clicks is ultrasonic, i.e. above the audible range of human listeners, but we are able to hear their lower frequency components. Sometimes the click trains run together in incredibly rapid ‘buzzes’, e.g. when they are homing in to capture a fish. Common dolphins use pulsed calls also (‘squawks’) and whistle. Whistles enable members of the school to keep in contact – common dolphins sometimes travel in huge schools numbering several hundreds of individuals.
A number of small crustaceans are able to make loud impulsive ‘snaps’ using their highly specialised pincers. Reefs in tropical waters can sound like frying oil due to the multitudes of ‘snapping shrimp’. Some culprits are well known, such as the pistol shrimp Alpheus. The source of snapping in UK waters is still a mystery however – it is a commonly heard sound, but the animals producing it are as yet unidentified.
The sounds produced by chains used to moor boats and navigation buoys, as they rise and fall in the waves, can be almost musical at times. The frequencies of the bell-like chimes vary with the size and thickness of the chain links. Underwater, small harbours can sound harmonious in calm conditions, with just occasional clinking, but distinctly discordant in heavy weather when all the chains are ‘calling’. In this way the underwater sounds capture an impression of the sea conditions at the surface. Underwater bells, in fact, were once proposed as a navigation aid for shipping – it was intended that ships deploying a hydrophone would be alerted to the proximity of coastal hazards at night and in thick fog.
Echosounders are used for gauging water depth, for finding fish or objects on the seabed. Pulses are transmitted from a vessel; the returning echoes are then received, processed and interpreted. The sounds produced by many echosounders are too high in frequency to be audible to the human ear – high frequency pulses provide information with greater resolution than low frequencies. However, low frequency pulses are able to travel greater distances through the water, and ships often include low frequency sonar (12 kHz is a common frequency) in their array of depth sounders. We hear ship’s sonar are single pulses at very regular intervals, typically 1-3 seconds apart.
Seismic surveys use powerful sound sources to obtain information on the structure of rocks in the earth’s crust. The aim is often to locate oil and gas reserves. The most common sound source is a coordinated array of airguns, towed behind a seismic survey vessel. Echoes returning from the junctions between layers of rock are recorded using hydrophones towed within long streamers. Seismic exploration may be audible over many tens of kilometres – listen for an initial low, boom, followed by a series of echoes. The airguns typically fire each 9-12 seconds.
Male common seals make fascinating sounds during the breeding season (June and July on the UK coast). They produce low frequency calls that could be described as ‘growls’ or even as ‘a bowling ball rolling down an alley’… It is assumed that the male common seals use these sounds to compete against other males and to attract females.
The song of the humpback is the most elaborate, complex and well-known vocalisations of the great or baleen whales. Singers are exclusively male, and will often hang stationary and upside down in the water column, calling for many hours at a time, pausing only to rise to the surface to breath. Males are believed to sing in order to compete against rivals and to attract female humpbacks. Singing takes place mostly on the breeding grounds, although it is also heard on migration and one some summer feeding grounds. All males in one breeding area sing approximately the same song – repeating a series of several ‘phrases’ in the same order, but the songs gradually evolve and change over time.
Many fish are vocal, although we are only beginning to learn about the sounds produced by even common species. Fish produce sounds in different ways, passing air through resonating chambers or rubbing spines or fins against their body for example. Typical sounds are single ‘grunts’ or short ‘moans’ produced in at intervals of a few seconds. Some particularly vociferous species create ‘fish choruses’ on reefs at certain times of the year.
Northern & Southern Right whales
Right whales communicate using a number of different, low frequency calls. A common sound that is used by both northern and southern hemisphere right whales is the ‘up- sweep’. This is a low frequency moan that sweeps upwards in frequency over about a period of 1 second. Right whales are endangered and protected throughout their range and Scientists use recordings of up-calls to determine when and where they occur. Up-calls appear to be a form of ‘contact call’, announcing the presence of individuals to other right whales. A second commonly heard right whale sound is the spectacular ‘gunshot’. This is believed to be an aggressive sound used between competitive males; many gunshots may sometimes be heard emanating from groups of whales that are actively splashing, charging and leaping at the surface.