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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

Acoustic buoy now detecting rare and endangered whales in New York Bight - An acoustic buoy making its first near real-time detections of two rare great whale species in the New York Bight, including the highly endangered North Atlantic right whale.
Narwhal echolocation beams may be the most directional of any species - Analysis of some of the first recordings of wintering narwhals showed that they may have the most directional sonar of any species. Understanding how these whales use sound could help predict impacts of Arctic change, say researchers.
Whale song 'GPS system': Previously unknown component of whale songs discovered - Researchers have known for decades that whales create elaborate songs, sometimes projecting their calls for miles underwater. A new study, however, has revealed a previously unknown element of whale songs that could aid this mode of communication, and may play a pivotal role in locating other whales in open ocean.
Genetic mutation in whale eyes may increase mortality risks - Difficulty seeing in bright light, which can be linked to a genetic mutation, can also increase baleen whales' susceptibility to fatal entanglements in fishing gear, say researchers.
Local fidelity key to ocean-wide recovery of humpback whales - Humpback whales can migrate thousands of miles to reach feeding grounds each year, but a new study concludes that their fidelity to certain local habitats -- as passed on through the generations -- and the protection of these habitats are key to understanding the ultimate recovery of this endangered species.