Excerpt:
To Whales, Our Plastic Debris Sounds Like Dinner…
We’ve likely all seen videos of how dark the deep ocean is.
Think of the scenes of deep-water submersibles exploring shipwrecks like the Titanic. It’s pitch-black, and the spotlights on the vessels barely penetrate the darkness to illuminate the wreck.
That’s because light’s brightness in the ocean decreases with depth. The National Ocean Service reports that while minimal light may be detected as deep as 1,000 meters (3,280 feet), there’s rarely any significant light beyond 200 meters (656 feet).
And that’s a huge problem if you’re a deep-diving whale looking for food. It’s impossible to see your next meal.
Scientists assume seals and toothed whales are washing up dead with stomachs full of plastic because they mistake it for food. Sadly, plastic bags and film can look like squid or jellyfish with wavy tentacles, especially if there’s not a lot of light.
That doesn’t explain, however, why deep-diving whales that use echolocation, like sperm whales and beaked whales, are ingesting plastic. So, marine scientists from Duke University, NC State, UNC-Chapel Hill and the National Oceanic and Atmospheric Administration compared the way sound bounces off plastic floating underwater to the prey that whales usually eat, namely squid and squid beaks.
Their study found that plastic bags “sound” a lot like dinner to a whale.
What’s echolocation?
Echolocation is the ability to observe an environment using sound.
To echolocate, whales use special organs called dorsal bursae to emit clicks and create echoes that bounce off objects and return information. The whale interprets the strength of the echo to help it find food, avoid objects and position itself in the ocean. The clicks are also used for social interaction.
Another way to think of those clicks is to listen for echoes when you walk through a tunnel or face a wall and yell.
But what if prey and plastic sound alike?
The study found that 100% of the plastics tested—things like plastic bags, rope and bottles harvested from the stomachs of stranded whales—have similar or stronger acoustic target strengths compared to squid.
That’s right: the sounds bouncing off a plastic bag or bottle sound just like a squid.
“Assuming these animals are ingesting plastic at depth and not at/near the surface, they are consuming plastic without visually identifying it,” noted a passage in the study. “Deep-diving toothed whales may therefore be misinterpreting acoustic cues when echolocating; presumably plastic’s acoustic signature resembles that of primary prey items, driving plastic consumption…”
