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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

A better pregnancy test for whales - To determine whale pregnancy, researchers have relied on visual cues or hormone tests of blubber collected via darts, but the results were often inconclusive. Research points to a weakness of previous testing and evaluation methods and provides a new hormone testing regime that offers better results.
Earthquakes disrupt sperm whales' ability to find food - Scientists studying sperm whales have discovered earthquakes affect their ability to find food for at least a year. The research is among the first to examine the impact of a large earthquake on a population of marine mammals, and offers new insight into how top predators such as sperm whales react and adapt to a large-scale natural disturbance.
Dolphins gather in female family groups - Social clusters including mothers' groups play an important role in the life of southern Australian bottlenose dolphins, a new study shows. Like giraffes, lions, hyenas and grey kangaroos, bottlenose dolphins appear to form social bonds with kin and other females in similar reproductive condition, while maintaining moderate and loose social bonds with some same-sex individuals.
Grey seals discovered clapping underwater to communicate - Wild grey seals can clap their flippers underwater during breeding season.
Marine heat wave linked with spike in whale entanglements - Climate change is increasing the frequency and severity of marine heat waves -- warm water anomalies that disrupt marine ecosystems -- and this is creating new challenges for fisheries management and ocean conservation. A new study shows how the record-breaking marine heat wave of 2014 to 2016 caused changes along the US West Coast that led to an unprecedented spike in the numbers of whales that became entangled in fishing gear.