Secrets of the sea: Sounds and sea creatures

Underwater sounds are important for animals. It allows them to navigate, hear the sounds of approaching predators and prey, and is a way of communicating with others. The increasing use of sound by people to explore the sea has raised issues about the effects of sea life.

People also use sound to explore the underwater world. Sound is used for many reasons including geological surveys and biological surveys and to locate oil and gas fields. To understand how humans use sound to affect animals, we need to learn more about the use of sounds of animals in the ocean.

How do animals hear underwater?

Sunlight through the water is not very good and visibility may be poor even in shallow water. Sound properties are an ideal way to communicate underwater so many animals use sound to communicate with each other and to ' observe ' objects in the marine environment.

Many marine animals have evolved many different ways to find and create sounds in the country. Most fish, except sharks and stingrays, have sensory hair cells in a small inner ear filled with viscous substances. Attached to the hairs, the scientific name is stereocilia and in the liquid of each ear is an otolith or ear bone. When sound waves pass through water and the body of the fish, otoliths tend to stand still, relative to the movement of the fish. Inertia of otoliths stimulates stereocilia to convey messages to the brain.

Another method uses closed air bags or lungs of mammals such as dolphins and whales or bubbles swimming in fish. The air in the swim bladder is easily compressed by sound pressure waves, which are converted into vibrations, allowing the fish to detect sound as well as vibrations. The sensitivity of fish to sounds and vibrations varies from species to species depending on the proximity of the swim bladder and the inner ear of the fish.

How do animals create underwater sounds

Crustaceans like crustaceans, which have exoskeleton, produce sound by rubbing or hitting a part of their body on another part of their body to make it vibrate, similar to the way insects create sound. The sound of ' splitting ' of animals like this creates a series of crisp sound pulses that can be heard at a distance. Because there are so many small creatures, they create most of the background sound in the ocean.

Fish have soft skin so they cannot produce sound in this way and must actively vibrate a certain part of the body. Some fish vibrate the air in their swim bubbles to make sounds and sounds then emit in the surrounding water environment.

Another way to create a typical sound is by whales and dolphins. In general, they produce sound by moving air from one compartment to another in the body through a valve with a vibrating ' lip '. Because the density of meat of a marine animal is equivalent to the proportion of water, the sound emitted in an effective way, is quite large and travels a long distance.

Echoes and echoes in echoes

Some animals such as whales and dolphins have evolved and used sonar (SOundigation and Ranging) or echolocation to create and detect sound. This compensates for the lack of visual information in the ocean. These animals produce a very high and short ' split ' sound by moving air through the vibrating ' lips ' in their heads.

Sound waves go in a predominantly forward direction, concentrated by a section above the head that contains fat. A part of the sound is echoed by objects such as a stone or a fish and then transferred to the eardrum of the ear through the lower jaw, the lower jaw also has a fat-filled area.

The delay for the impulse path is about 1.5 milliseconds per meter moving but also long enough for the animals to locate the object. Repeated pulses help the animal reduce the effect of background or noise from other animals, and the exact frequency of the return noise gives information about the movement of the object.

Depending on the size of the target, echolocation is useful in the tens of meters or more. Some animals have developed a remarkable ability to discriminate sensitive: dolphins can detect the difference between a solid and a metal ball that is concave with a size of one. baseball with a distance of 20 meters.

Noise in the ocean

Ocean background sounds are created by the sound of waves, wind and rain and by a large number of small crustaceans and other animals. Typical background sound level is about 100 decibels (dB). Wind and waves in the storm, and ' choir ' from fish and invertebrates can increase this level to about 120dB.

Measurements show that the Pacific Ocean is still quite quiet and most background sound is caused by wind and sea creatures. This is in contrast to the Atlantic Ocean, where most of the background sound comes from propellers hitting waves of the ocean.

Noise levels from artificial sources and animals.

The chart below shows the frequency distribution of pressure levels from natural and artificial sound sources in Australian waters. Decibel numbers are low because they show levels of sound pressure in individual bands just 1 hertz wide at each frequency. The numbers of all these bands must be added to obtain the total sound pressure.

Within 1 meter of a typical sonar converter, the sound power level can be up to 180dB, comparable to the highest level of animal cries. But human sonar transmitters can be arranged in long lines so that the signal maintains high power at significant distances.

The loudest cries in the ocean, such as seals and whales, in a distance of 1 meter their cries are up to 190dB, which is equivalent to the sound power level of loud human voices in the air. with the same distance. Some echolocation sounds can reach 230dB, although only for a very short time.

Other sounds in the ocean, including undersea earthquakes and volcanic eruptions on the sea floor, are recorded with levels of echoing echoes of echolocation, reaching more than 240dB in very areas. wide. Are people using sonar harmful to ocean animals?

The potential effect of sonar on marine animals is similar to that of humans exposed to noise:

· Behavior change
· Loss of ability to hear temporarily or permanently or damage tissue and
· Physiological stress response

These species are affected by sound depending on the frequency and level of sound pressure. For example, sound sources such as air rifles produce more noise in the baleen whale's hearing range than low-frequency echo detectors, but these detectors produce more noise. in the range of toothed seals and whales. Sounds that affect this species may not affect other species.

The potential risks to animals due to human use of sound are due to the combination of the energy level, frequency and sound in the water created by underwater ' terrain '. Properly low-capacity and high-frequency devices create a serious risk. The highest risk devices are air guns and high-power converters with wide beam angles.

How do we get results if animals are affected by sound?

It is not always easy to determine whether an animal is hurt when exposed to sound. Biologists and engineers have developed a new digital card, which can give information about whale behavior, including how deep they dive, what they hear and what they make sound. What to communicate. This card can help with controlled experiments rather than just random observations of animal behavior that occurs once. CT and 3D techniques are also being used to study the structure of the sea mammal's ears and how they can be injured when exposed to sound sources.

Safety and sound

Several studies have been carried out to investigate the potential impact of humans using sonar for research purposes, especially in calm natural waters around Antarctica. International guidelines have been developed for the use of sonar, to minimize the possibility of injury or disturbance to marine animals.

These measures include using the minimum amount of sound energy required and using very little at times when animals are more sensitive to harassment, such as breeding or mating. Researchers document the details of sound activities, to allow for an up-front evaluation of the cause of any future changes to the distribution, quantity or types of dynamics. object.