How far can sound waves travel?
Orientation and navigation of the whales
Numerous species of whales migrate - and cover very long distances in the process. Most noticeable are the migrations of baleen whales. In summer you can find the animals in the polar waters, where they eat up reserves in the nutrient-rich waters. The migration to tropical regions begins in autumn, where the whale cows give birth in the warm water, because the newborns could hardly survive in the cold polar water. The whale bulls follow the females to the warm birth regions, as the latter are in heat in the tropical latitudes and are ready to mate. Gray whales cover 6,000 to 8,000 km on their migrations from the Bering Sea and the adjacent northern areas to the California coast.
Among the toothed whales, however, only a few species migrate such as B. the sperm whale, which regularly covers the long way from the European North Sea to the African coast. Many whale species in tropical and subtropical latitudes, as well as species that live near the coast or in rivers, do not migrate.
An interesting aspect of whale migration is the time-shifted migration of different species. Most furrow whales, which occur in both the northern and southern halves of our planet, migrate at different times. While winter is in the north and this population is close to the equator, the southern population is currently in the Antarctic latitudes. There is hardly any (genetic) exchange between the two populations.
The ability of the whales to keep the direction on their annual migrations and thus to ensure the survival of the species will be examined in more detail below. And also possible causes for the incorrect orientation that lead to the often fatal strandings.
On December 4th, 1997 13 young sperm whales stranded on the North Sea island of RÃ¸mÃ¸ in Denmark. They had evidently lost their way on their migration from the western European Arctic Ocean across the Atlantic to the African coast. The shallow waters of the North Sea, shallow beaches, and the unknown area led to further disorientation and stranding. The dead weight of the eight to 14 meter long animals of up to 70 tons resulted in fatal injuries to the internal organs on land.
Do whales have ears?
The environment in which whales have established a permanent place is very different from ours, because the light is filtered out by the water very quickly, so their eyesight is far less important than for most land animals. Even in clear waters there is no more light below approx. 400 m. But how can the animals orientate themselves then? As the anatomy of the brain suggests and behavioral studies confirm, whales have completely lost their sense of smell. But how is the sperm whale able to find its main food, squid, which it looks for at depths of less than 500 m?
The whale's sense of hearing
Water is physically denser than air, which is why it transmits sound waves faster and further. Whales have adapted to this and developed very good hearing.
However, the outer ears disappeared early on as an adaptation to the demands of a streamlined body. The small opening that leads to the inner ear can only be seen as a tiny hole just behind the eyes.
The inner ear was also heavily reshaped. Above all, the area of the actual hearing organ, the cochlea (dt. Snail), is not built into the skullbone, as is the case with humans, but lies - through foam-filled cavities, acoustically isolated from the skullbone by air - on the back End of the lower jaw.
This is necessary because sound waves in water are transmitted directly through the skull bones of a mammal. This is not the case in air, because here the main parts of the sound are not transmitted from the skull bones but to the hearing organ via sound conduction in air (auditory canal). Thus, the sound in the air reaches the cochlea, which is further away from the sound source, later and more attenuated than the hearing organ closer to the sound source. In water, on the other hand, in humans the signal strengths are transmitted equally in both hearing organs. Because of this, people who submerge their heads in water are unable to perceive the direction of a sound source.
The foam surrounding the snail of the toothed whale retains its acoustic insulating properties up to a pressure of 100 atmospheres (this corresponds to a diving depth of 1,000 m). In this way, a whale can locate the direction of sound even during a deep dive.
The whale's echo sounder
Toothed whales are able to increase the amount of sound information through the use of an echo sounder system. The animals emit clicks that are thrown back from the sea floor, from the surface of the water and every solid body in the vicinity and are picked up by the whales as echoes. This echo informs the toothed whale about the type, shape and quality of an object. The way in which the object - for example a potential prey animal - is moving is also perceived in this way.
The time between sending the signal and receiving its echo provides information about the distance between the object and the toothed whale. With the help of this bio-sonar, the marine mammal can locate, track and catch fast swimming prey in absolute darkness.
The click sounds in the context of echo orientation differ from the whistling, grunting and other sounds that are used to communicate with conspecifics.
The typical clicks are very short (less than 1 millisecond) and are repeated many times per second, so that the sequence sometimes sounds like the creak of a door to the human ear.
In the larger sperm whale, the individual sounds last longer and are repeated less frequently.
The sound intensity is distributed over a broad frequency spectrum, the majority of which is above the human hearing ability. In much the same way as we direct the beam of light from a flashlight or a flashlight onto an object that we want to see at night, toothed whales can focus their orientation sounds and direct them towards an object. This creates a stronger signal that works over greater distances. This view is shared by many whale researchers; however, there are different theories about how the sounds are made and how they are bundled. One theory is that the sounds are bundled with the help of the melon, a fatty tissue in the forehead of toothed whales (see drawing above).
Gray whales are probably the most widely watched whales. The migration of gray whales from their summer grazing grounds in the Bering Sea and the adjacent northern areas to the breeding and mating sites in Baja California and back is particularly interesting for many people. Between December and April, whale cows and bulls mate in the lagoons off the coast. The young are born about 12 months later. Depending on the mating season, these are born on the way back to the lagoons or in the lagoons themselves. The longest migratory distance of all mammals lies between mating and birth. The gray whales cover distances of 6,000 to 8,000 km.
How do whales find their routes around the globe?
In various studies it was found that the migration routes of whales from the grazing grounds of the polar regions to the "nurseries" in warmer waters often run along magnetic fields. Behavioral studies have shown that fin whales off the northeastern United States, for example, regularly follow magnetic fields instead of crossing them. A comparison of places where living whales are stranded shows that magnetic lines often run perpendicular to the coastline, but there are hardly any geographical or physical similarities.
From these results the conclusion - which is undisputed among whale researchers today - was drawn that marine mammals use an invisible "source of information": the earth's magnetic field.
The earth has a magnetic field that is roughly aligned with the poles. A magnet that can swing freely around its vertical axis positions itself in the direction of the magnetic field lines.
It is known of many organisms that they can perceive the earth's magnetic field and adjust their behavior accordingly. Birds navigate to a certain extent with the help of this sense. In anatomical studies, tiny amounts of magnetic material have now been found in the brains and around them of various species of whale.
All of these findings indicate that whales have the physical ability to sense geomagnetism and use it to navigate the oceans.
Whale protection - underwater noise as a cause of whale stranding?
Environmentalists suspect that the "acoustic pollution" is the reason for the misorientation and stranding of whales. However, scientists are still arguing violently about the connection between the increasing underwater noise - caused by oil test drilling, the hammering of ship engines and drilling stations - and possible damage to the acoustically oriented marine mammals.
These assumptions are confirmed in a study presented in 1999 by the environmental organization "Natural Resources Defense Council". The study shows that in certain sections of the California coast where the noise level is high underwater, many marine life has disappeared. In the opinion of the environmentalists, whales will also be driven away from their migration route and their traditional breeding grounds by the increasing noise.
The biologist Dr. Michel AndrÃ © from the University of Las Palmas de Gran Canaria believes that he has also discovered evidence of this connection during sonication tests on sperm whales:
Sperm whales living in the Canary Islands react too slowly to avoid collisions with ferries because they have got used to the underwater noise caused by the heavy shipping traffic. The constant noise level could have caused the animals' hearing ability to deteriorate, especially in the low frequency range.
A solution to the problem can be seen in an effective warning system that does not harm sperm whales and does not drive them out of the sea area that is important to them.
The United States has already responded to the above-mentioned relationships. An obligation to report for shipping on the east coast is intended to prevent collisions - especially with the rare northern right whales, whose population is estimated at around 300 individuals in the North Atlantic. Almost half of all known deaths of these marine mammals are due to collisions with ships.
According to the new regulation, since the end of June 1999 all larger ships have to report their position to a central computer when they navigate the waters off the Cape Cod peninsula and the US states of Florida and Georgia. Then this computer informs you of the last whale sightings in your sea area.
The US Navy is exempt from the reporting requirement, but it wants to join voluntarily.
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