Sei whales might be among some of the largest animals on our planet, but it can take something very small and seemingly innocuous to harm them. For the unfortunate whale found dead in the Chesapeake Bay area in the US last year, that something was a black plastic DVD case.
When biologists at the Virginia Aquarium and Marine Science Center heard rumour of a 45-foot (13.75 metre) sei whale, an endangered species, bobbing along a tributary of Chesapeake Bay, they knew something was very wrong. The whale was disoriented, thin and headed nowhere fast. "She was at the wrong place at the wrong time," aquarium research coordinator Susan Barco told National Geographic.
In an attempt to save the animal, Barco and her team followed it for several days, hoping to deter the whale from colliding with any boats on the river and to gain a better understanding of what caused it to stray so far from its offshore feeding grounds. Despite their best efforts, the whale sadly died days later ... but its death did allow Barco to finally see the full picture. A necropsy revealed a disturbing culprit behind the whale's demise: a black plastic DVD case! The rigid plastic edges had lacerated the whale's stomach – preventing the animal from feeding properly. "It makes me very sad that a piece of plastic that was not disposed of properly ended up killing [this] whale," she said. "It was a preventable death."
The DVD death seems like a strange and exceptional case, but the sad, hard truth is it's not that astonishing given the six million tonnes of marine litter dumped into the oceans every year. Marine pollution is a well-publicised problem ... what might come as a surprise is that we don't actually know the extent to which it affects ocean giants like this sei whale.
"The last few years have seen the impacts of [plastic] documented in a wide range of species, from plankton and fish to marine megafauna," explains the Environmental Information Agency (EIA), whose recent study revealed that ingested plastic debris has now been documented in 56 percent of all cetacean (whales, dolphins and porpoises) species – a very disturbing fact considering that only a fraction of dead whales are ever found by scientists.
"Detection of this plastic debris in cetaceans largely depends on the data provided by stranded animals, presenting only a snapshot of the impacts occurring unseen at sea," the EIA notes.
In order for scientists to name a plastic-induced cause of death in a large marine mammal, the animal has to actually end up on a beach and then be found and reported to the appropriate authorities before it starts decomposing (exploding whale, anyone?). To compound the problem, very few stranded animals arrive in good enough condition to receive a necropsy in the first place. "What we end up with is a considerable knowledge gap concerning the extent of the impact plastics have on [whales and their kin]," adds the EIA.
To better understand which types of debris most commonly cause whales to die, lead researchers Sarah Baulch and Clare Perry combed through years of stranding records collected in 14 countries. Nets, lines, ropes, traps, plastic particles, bags, containers, fabric, rubber, paper, cellophane, polystyrene, glass and a slew of other unidentified items were among the types of trash found inside the stranded animals. Perhaps most shocking was a 16-square-metre piece of plastic sheeting found inside of a sperm whale in 2010!
The researchers also found that 'death by plastic snack' has been documented in 48 different species of whales, dolphins and porpoises – a key finding as it demonstrates that plastics are affecting species that use a wide variety of feeding strategies and live at different levels of the water column.
"Plastic waste presents an unavoidable challenge ... Although [some of its] impacts remain unknown, marine debris interactions can have severe welfare implications, [and present] a threat to more than 300 other species of marine fauna," the authors say, adding that we can't wait until we know the full extent of problem to find a solution if we intend to save these iconic species.
Top header image: John Schneider/Flickr