Sink a hydrophone in the ocean and discover a marine jungle of animal noises from the tiniest shrimp to the largest blue whale. Marine life depends on this soundscape for mating, finding food, navigation and avoiding predation.
This ocean cacophony was all natural until the advent of the industrial revolution when human-made sounds from blasting, drilling, military, and shipping began drowning out these important biological cues. Imagine, if you will, not Rachel Carson’s famous silent spring, but the opposite. Imagine if there was so much human-made noise in the spring that it drowned out all of the birds’ calls. What would happen to those birds? For marine life, the intrusion of these sounds in the mix is the equivalent of being asked to wear a blindfold.
So what’s at stake for our world’s oceans and for us? Here are six amazing things about sound and marine life:
- About half of all fish species are estimated to emit sounds. These sounds help fish find spawning grounds and function like the call of a bird does, as specie specific signatures. By understanding and tracking these sounds, scientists can also identify important spawning grounds in the oceans, track numbers of individuals in a species, and by doing so more strategically protect these important spawning areas.
- Scientists have discovered that each whale population has its own “language,” which is understood only by individuals of the same population. For a population that migrates hundreds of miles of ocean basin from feeding to mating grounds, most whales depend on hearing these songs to find other individuals to accurately navigate.
Impeding this important whale communication by drowning in human-made sound has implications for fisheries. Recent science has found (perhaps counter-intuitively) that increasing the population of large whales might help to increase the number fish in the ocean.
- As the largest creature on Earth, blue whales can also boast of being the loudest. At 188 decibels, their loudest vocalizations can be heard a thousand miles away and is louder than a jet, which peaks at only 140 decibels. Humans can’t hear most of the blue whale’s song, however—it’s too low. They sing at frequencies between 10 and 40 Hz (the unit measurement of sound frequency) and infrasound under 20 Hz cannot be heard by humans. While other large whales are rebounding, blue whales do not appear to be. Blue whales number in only 1% of their historic population. Scientists speculate their lack of comeback is due to the wide scale disruption of the marine ecosystem in the Southern Hemisphere by the blue whales population’s decimation. Without blue whales, there had been a cascade of other marine life losses that has made for a severely altered environment, one that continues to be difficult for other marine life to survive and rebound
- Dolphins are thought to have an individual signature whistle, invented as a calf and kept throughout its life. They use these whistles to call to one another and seem to be able to remember the calls of other individuals for decades. No other species other than humans and dolphins has been shown to have this capacity.
- Noise has always been a driver of evolution and adaptation in the sea, providing “acoustical niches” inhabited by different species. Scientists speculate that the ocean was actually noisier in pre-whaling 1800, before the addition of human generated noise. This speaks volumes about the biomass of a “healthy” ocean pre-1800 as compared to now.
- There is no place to escape from the intrusion of human-made sounds in the ocean. Sounds from shipping were recently recorded at the very deepest part of the ocean: the Mariana Trench, at 10,000 meters under the sea.
Join us at Beeps, Rumbles, and Blasts: How Human-Generated Noise Threatens Marine Life on April 7th featuring Dr. Christopher Clark of Cornell University and Dr. Scott Kraus from the New England Aquarium. For a sneak preview hear Dr. Clark speak briefly about the importance of this topic in this beautiful and short NPR production
“[If] I’m a blue whale my heart beats once a minute. My ‘metronome’ is completely different from yours. And yet I, as human observer, am expecting their communication to be somehow synchronized with mine? Whales have their own listening culture. It will take a long time to begin to understand it.” – Dr. Christopher Clark
Blog contributor Laura Parker Roerden is Executive Director of Ocean Matters and is on the board of Women Working for Oceans.