Millennial Mysteries: Beached Dolphins often Deaf, Study Finds

Image © REUTERS/Andres Stapff.  Image Source: Time.

Picture Caption from Time: Richard Tesore, head of the NGO Rescate Fauna Marina, holds a baby La Plata river dolphin in Piriapolis, Uruguay. The dolphin, which was found on the beach in the city four days ago, is recovering at the reserve from injuries believed to have been caused by a fishing net.

Many mysteries that appear to characterize the apocalyptic subtext of our times are often cryptic clues to how the world is changing as a result of technological innovation. Why are whole colonies of honeybees dying amid reports of colony collapse disorder?  Cell phones.  Why are dolphins and whales beaching themselves in record numbers?  A new report out states that the animals who weirdly swim into fishing nets, or swim ashore, usually to their deaths, are often deaf or partly deaf.

From the Time report: "Finally, an answer to the question of why such highly intelligent animals do something so seemingly dumb. Each year, some 1,200 to 1,600 whales and dolphins are found stranded off coast in the U.S. But thanks to a study that examined brain activity in dolphins, scientists may finally have a clue as to why so many of the playful sea creatures end their life on shore.  A study published in the PLoS One journal concluded many dolphins who wash ashore have one thing in common: they are nearly deaf.  The study speculates that hearing impairment leaves the animals unable to use sound to find food or family, which can cause them to grow weary and wash ashore. By the time we humans find them they are often very weak or already dead ... researchers aren't sure what is causing the hearing loss — it could occur at birth, happen as a result of old-age or as a consequence of man-made noise, such as Navy sonar."

Why are cetaceans going deaf?  Is it sonar?  The journal article suggests that PCB pollution in the oceans is contributing to congenital deafness: "It is likely that hearing loss was congenital in some of these stranding cases, especially two of the rough-toothed dolphins (Dancer and Vixen), which were estimated to each be approximately two years old at the time of stranding. Congenital hearing impairment in humans is not uncommon. In one study, 113 out of 52508 (about 2 out of 1,000) newborns screened in Texas had hearing loss. In addition to genetic factors related to hearing loss, one extremely important, unexplored mechanism may be the impacts of chemical pollution on hearing. Cetaceans, particularly odontocetes, have been shown to accumulate very high levels of polychlorinated biphenyls (or PCBs), which can be maternally transferred to offspring. Evidence from studies with rats suggests that these chemicals may affect how hearing develops. In fact, it has been shown that developmental exposure of rats to PCBs results in severe hearing loss. It is not known how these or other contaminants might affect ear development in cetaceans."