Thus far, no cause has been determined, although evidence of middle- and inner-ear damage, lung lesions and bubbles in the blood are consistent with acoustic impact and decompression syndrome, leading to speculation that oil exploration in the region may be to blame.
In a statement released earlier this month, BPZ Energy confirmed that it was conducting acoustical, seismic studies in the area, but that the dolphin deaths began more than 2 weeks before exploratory activity commenced.
In the majority of large marine mammal strandings, no definitive cause is found – in part, because multiple factors are frequently at work. Toxic pollutants, for example, might weaken an animal’s immune system, making it more vulnerable to bacterial or viral infection. Persistent organic pollutants that accumulate in organisms further down the food web also tend to become more concentrated in top predators such as dolphins.
A severe lack of resources makes it even less likely that a cause or even the full extent of the Peruvian event will ever be known.
Much of the information about the current stranding comes from an investigation conducted by Dr. Carlos Yaipen Llanos, from the marine mammal rescue team ORCA Peru, and Hardy Jones of BlueVoice. Traveling 135 km along the coast of northern Peru in late March, they encountered more than 600 stranded dolphins — males, females, pregnant females, calves and newborns.
Roughly 90 percent of the animals Llanos and Hardy found were long-beaked, common dolphins, which tend to swim close to the ocean surface. The remainder were Burmeister’s porpoises, which feed in deep water but approach the surface when giving birth. All of the Burmeisters were pregnant, nursing or newborn calves.
BlueVoice has posted a video produced by Hardy, which contains imagery that some may find disturbing.