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Dolphins

Earth Platform > Animals > Marine Life > Dolphins
Every seven years, half of all dolphins in captivity die from marine pollution, habitat degradation, harvesting, low frequency sonar, entrapment in fishing gear and other stress-related illnesses. Luckily, a number of countries have now stopped or reduced the capture of wild dolphins, and knowledge and conditions are vastly improving. However, there are still many countries where conditions for captive dolphins are well below standards.
 

Dolphins

A lot of dolphins die in fisheries. In the North Sea alone, an estimated 10,000 harbour porpoises are killed in fishing gear each year.  In recent years there have been gear modifications  that make it possible for the dolphins, to escape once a fishingnet is closed. Not every country has made these modifications mandatory yet, so dolphins are still killed in this fishery. The dolphins killed in fishery are mainly common dolphins, spotted dolphins and spinner dolphins. Occasionally other species, including bottlenose dolphins, are caught as well, but their numbers are lower.

dolphinsEspecially in coastal areas, marine mammals are often disturbed by human activities. Collisions with boats and jet skis have already resulted in severe traumas and even deaths of marine mammals, including dolphins. Also, boat traffic in areas where dolphins usually rest or forage can disrupt their normal behaviour. The seemingly harmless human behaviour, such as swimming in areas where dolphins naturally rest, can result in disturbance and changes in behaviour. In a bay in Hawaii for example, where spinner dolphins came to rest, the increase in swimmers, has resulted in the dolphins leaving the bay. They had to find another resting area.

Dolphins are very acoustically oriented animals. With their natural sonar, they rely heavily on sound for their orientation, navigation and communication with other dolphins. Since the last century, the increase in boat traffic around the globe has resulted in a considerable increase in noise in the world's oceans. This has a negative effect on dolphin and whale navigation and communication. 

 

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Dolphins in the news

Dolphins and Whales News -- ScienceDaily

Beaked whales' incredible diving abilities confirmed - A new study provides the first record of the diving behavior of Cuvier's beaked whales in US Atlantic waters. The species is Earth's deepest-diving mammal but spends very little recovery time at the surface. The new data, from 5,926 dives recorded off Cape Hatteras, N.C., shows them routinely diving more than a mile while holding their breath for over an hour. These whales push the limits of mammalian physiology.
Plastic in Britain's seals, dolphins and whales - Microplastics have been found in the guts of every marine mammal examined in a new study of animals washed up on Britain's shores.
Why do beaked whales return to a Navy sonar range despite frequent disturbance? - Using data from underwater robots, scientists have discovered that beaked whales prefer to feed within parts of a Navy sonar test range off Southern California that have dense patches of deep-sea squid. A new study shows that beaked whales need these prey hotspots to survive, and that similar patches do not exist in nearby 'sonar-free' areas.
Humpback whales' songs at subarctic feeding areas are complex, progressive - Humpback whales overwintering in feeding areas may sing complex, progressive songs which closely resemble those associated with breeding grounds, according to a new study.
Piece to the puzzle of baleen whales' evolution - A researcher has added another piece to the puzzle of the evolution of modern baleen whales with a new study examining the teeth and enamel of baleen whales' ancestors.