Why are thousands of dolphins dying off the coast of Peru?

For the past three months, something has been very wrong along the Peruvian coast. Nearly 3,000 dolphins have washed ashore dead, making it one of the largest marine mammal die-offs ever recorded...and it likely isn't even close to over.

Such animal die-offs aren't totally unheard of - you may remember all those birds and fish dying en masse back in late 2010 and early 2011 - but they are a little rarer in large mammals like dolphins. And the sheer scale of what's going on in Peru is nearly unprecedented, and there's a very good chance that will end up being the largest dolphin die-off in recorded history. The question, then, is what could possibly cause 2,800 dolphins and counting to suddenly die?

Scientific American attempts to unravel that enigma, but they say there's every chance that we'll never really get to the bottom of what's going on here. There often just isn't enough knowledge available for these dolphin species - particularly somewhere like Peru, which isn't exactly known for its marine research - to draw definitive conclusions, and even then there's no guarantee that these zoological tragedies can be traced to a single root cause. One possibility, according to Carlos Yaipén - a veterinarian and found of Peru's Scientific Organization for the Conservation of Aquatic Animals - is that the acoustic waves created by nearby oil tests or sonar sweeps actually crippled the dolphins:

All of the 20 or so animals Yaipén has examined showed middle-ear hemorrhage and fracture of the ear's periotic bone, lung lesions and bubbles in the blood. To him, that suggests that a major acoustic impact caused injury, but not immediate death. Most of the dolphins apparently were alive when they beached, or had died very recently. "The animal would become disoriented, would have intense pain, and would have to make a great effort to breathe," he said of the injuries.

Unfortunately, that's just one of a few possibilities. These dolphins may simply not have strong enough immune systems to deal with new pathogen strains. The fact that 90% of the dead dolphins are long-beaked common dolphins - which are native to Central American waters and likely migrated relatively recently - may also be a factor, as the species may be struggling to adapt to the unfamiliar Peruvian waters. For an excellent, if not exactly uplifting overview of what's happening off the coast of Peru and in previous such die-offs, check out Scientific American.

Image by lowjumpingfrog on Flickr.