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.

Especially 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. 

Blue whales switch to daytime singing before migrating - Through the use of two advanced audio recording technologies, researchers have found that blue whales switch from nighttime to daytime singing when they are starting to migrate.
Vessel noise present year-round at Cordell Bank National Marine Sanctuary - The environment in the Cordell Bank National Marine Sanctuary off the coast of San Francisco is not a refuge from the noise generated by ship traffic, the first underwater marine acoustic study of the region has shown.
Call of the wild: Individual dolphin calls used to estimate population size and movement - A new study has shown for the first time that acoustic monitoring can be used in place of photographs to generate abundance estimates of dolphin populations.
Ichthyosaur's last meal is evidence of Triassic megapredation - Some 240 million years ago, a dolphin-like ichthyosaur ripped to pieces and swallowed another marine reptile only a little smaller than itself. Then it almost immediately died and was fossilized, preserving the first evidence of megapredation, or a large animal preying on another large animal.
Study finds high levels of toxic pollutants in stranded dolphins and whales - Researchers examined toxins in tissue concentrations and pathology data from 83 stranded dolphins and whales from 2012 to 2018. They looked at 11 different animal species to test for 17 different substances. The study is the first to report on concentrations in blubber tissues of stranded cetaceans of atrazine, DEP, NPE and triclosan. It also is the first to report concentrations of toxicants in a white-beaked dolphin and in Gervais' beaked whales.