SINKING FORTUNES: Threats to dolphins include certain tuna fishing practices and run-off of agricultural and industrial chemicals into rivers that drain into coastal areas of the ocean where dolphins spend much of their time. Pictured: bottlenose dolphins. Image: Tom Brakefield, Thinkstock By Roddy Scheer and Doug Moss
27 May 2011 Dear EarthTalk: How are wild dolphins faring on the high seas? Recent reports of dolphin deaths in the Gulf of Mexico may well be due to last year’s BP oil spill, but I imagine there are many threats to dolphins from pollution, human overfishing and other causes. — Henry Milken, Atlanta

Dolphins are probably the most iconic and best loved species of the marine world. Their playful nature and high intelligence have endeared them to people for eons. But our love of dolphins might not be enough to save them from extinction brought on by overfishing, pollution, climate change and other environmental affronts perpetrated by humans. The nonprofit International Union for the Conservation of Nature (IUCN), which maintains a worldwide “Red List” of at-risk wildlife species, considers 36 of the world’s 40 different dolphin species to be in trouble. Yes, specific events can cause problems for dolphins—researchers believe that the deaths of 300 dolphins in the Gulf of Mexico over the last year can be blamed on the BP oil spill there. But more widespread and constant forms of pollution—such as run-off of agricultural and industrial chemicals into rivers that drain into coastal areas of the ocean where dolphins spend much of their time—are having a more lasting negative effect on dolphins by poisoning them and causing reproductive problems. Also, dolphins have long been the unwitting victims of fishermen targeting large prey, such as tuna. According to Defenders of Wildlife, fishermen started to notice a half century ago that schools of yellow fin tuna seemed to follow dolphins that swim higher in the water column, especially in the Eastern Tropical Pacific. “Fishermen there have consequently found that setting nets on dolphins to catch the tuna swimming underneath is a lucrative technique for tuna fishing, despite the fact that the practice is extremely injurious to dolphins,” reports the group, adding that some seven million dolphins have since been killed as a result of the practice. Also, our unrelenting demand for seafood—which has caused rampant overfishing throughout the world’s oceans—means that dolphins, which feed on smaller fish such as mackerel, cod and herring as well as squid, are having a harder and harder time finding food. And in Turkey, Peru, Sri Lanka, Japan and elsewhere, dolphins are hunted as a delicacy and also to decrease competition for fish resources. As if these problems weren’t enough, climate change also looms as one of the biggest threats of all to dolphins. “Due to the rapidly rising oceans temperatures, the dolphin’s primary food sources are seeking deeper cooler waters,” reports the Defenders of Wildlife. “Scientists are concerned that the dolphins will have difficulty adapting as quickly as necessary to find new feeding grounds to sustain their populations.” …

Flipped Off: Pollution and Overfishing Spell Trouble for Dolphins Worldwide