On the weekend I had the chance to watch the movie Dolphin Tale. Without giving too much away, a dolphin gets caught in a discarded crab trap, beaches, gets tail amputated, gets a prosthetic tail, learns to swim, saves a young boy and ultimately fulfills the save the orphanage trope, substituting the orphanage for the Clearwater Marine Hospital. While the movie left some people in tears (happy tears, it is a family movie), it left me thinking about marine mammal stranding events.
Earlier this month thousands of either dead or dying dolphins washed ashore in Peru. The death toll (roughly estimated to be as high as 2800) is the largest dolphin die-off ever reported. The cause of this stranding (which has been ongoing since January) is unknown and given that only 50% of strandings worldwide have been able to identify a cause, it is likely that this mass die-off in Peru will remain a mystery. One theory for the strandings is major acoustic impact injury from testing for oil. Indeed, upon necropsy all the dolphins showed middle-ear hemorrhage and fracture of the ear’s periotic bone, lung lesions, and bubbles in the blood – symptoms of acoustic impact. However, Darlene Ketten, from Woods Hole Oceanographic Institute in Cape Cod, likens stranding events to car crashes, noting that “a lot of things can go wrong, but you get the same result“. Other causes of strandings can include, unknown virus or pathogen, stress, ship collisions, pneumonia, trauma, red tides, accumulation of environmental contaminants, anomalies in the magnetic field, and acoustic impact caused by sonar.
The recent death of a killer whale off the coast of Washington State has sparked renewed interested into the effects of sonar on marine mammals. Days prior to the discovery of the orca, the HMCS Ottawa was conducting sonar training and WarGames exercises off the waters of Victoria, BC, in the somewhat general vicinity of the orca. Initial examination of the orca showed signs of head trauma, but were inconclusive. While the cause of death for this orca will likely never be known, it does raise issues about protecting marine mammal habitat, not just the physical habitat, but also the acoustic habitat. With the increased volume of shipping, offshore oil and gas drilling and exploration, the noise in the ocean is getting Extremely Loud & Incredibly Close for marine mammals. In fact ocean noise levels have been doubling ever decade for the past 50 years! This ocean noise has the potential to disrupt whale behavior, even over great distances, as whales and marine mammals live in an “acoustic-dominant” world, as they use sound as the primary means for interpreting their underwater environment. Thus, all this chronic anthropogenic background noise creates conditions for the whales akin to those we would experience walking though a dense Fog. The question of what to do about this noise is puzzling, and a difficult task, especially when considering the sheer volume of shipping that occurs. Below is a visualization of how ships moved goods and people around the world from the mid-18th century to the mid-19th century compressed, as if they had occurred in one year
While these results are from the mid-19th century, it is not difficult to imagine a similar scenario being played out in the 21st century, and realize It Might Get Loud in the ocean. Yet there are signs of hope, Chris Clark, from Cornell University’s Bioacoustics Research Program, describes his experience hearing a blue whale off the coast of New York.
It is truly a beautiful, and unique sound, so much so that when Carl Sagan was chairing a NASA appointed committee to determine what the Golden Record to be shipped off with Voyager should contain, he decided to include recordings of whale songs. While this may seem like a cool thing to do, the problem is that we don’t know what the whales were saying, maybe they were saying “please be quiet”, or something that would enable the plot for Star Trek IV: The Voyage Home