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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

'Biological passport' to monitor Earth's largest fish - Whale sharks, the world's largest fish, roam less than previously thought. This new study used stable isotope analysis to demonstrate that whale sharks feeding at three disparate sites in the Western Indian Ocean and Arabian Gulf rarely swim more than a few hundred kilometers north or south from these areas according to researchers.
Whales use song as sonar, psychologist proposes - A psychologist has proposed that humpback whales may use song for long-range sonar. It's the singing whale, not the listening whale who is doing most of the analysis. If correct, the model should change the direction of how we study whales.
Satellite tracking reveals Philippine waters are important for endangered whale sharks - A new scientific study has tracked juvenile whale sharks across the Philippines emphasizing the importance of the archipelago for the species. The study is the most complete tracking study of whale sharks in the country, with satellite tags deployed on different individuals in multiple sites.
Novel approach studies whale shark ages the best way -- while they are swimming - A new study of whale sharks, using a novel approach to gathering data, shows these endangered animals can live longer and grow larger than previously believed.
The freediving champions of the dolphin world - New research explains how some populations of bottlenose dolphins can dive to almost 1,000 meters while avoiding decompression sickness. The new hypothesis suggests that lung architecture and the management of blood flow allow bottlenose dolphins to access oxygen in the lungs while preventing uptake of nitrogen which would cause the bends. The findings act as a starting point to understand how environmental changes and anthropogenic interaction may impact the future of the species.