Part two: The Conductor’s Conundrum
Tuning in to the underwater world has a conservation imperative that goes beyond connecting to a more comprehensive understanding of the life histories of whales; it is critical in an ocean where many voices now compete to be heard. A new study tests a hydrophone array that relays sonic data in real time in Squally Channel in British Columbia and helps us understand how sound data might better protect whale populations where humans and ocean animals share an increasingly busy space. In a conversation with Dr Ben Hendricks, Lauren De Vos delves into what it takes to make sound science work in remote locations. The implications mean a great deal for how we understand sound to protect critical ocean spaces and how we use it to manage busy shipping areas.
I hear them long before I see them: a high-pitched whistle as I sink my head below the water, the trill of an aquatic Mozart’s Zauberflöte directing my attention to the right. A volley of staccato clicks follows, seconds before a chattering pod of Indo-Pacific bottlenose dolphins swims into view. Off the coastline of Mozambique, this resident group of social dolphins flouts immigration laws as it traverses the invisible border that marks the end of South Africa at Kosi Bay and the start of Mozambique at Ponta do Ouro. I’m swimming in surround-sound, squeaks and whistles filling the water around me. The well-spotted underbelly of an aged male flashes past, his clarinet contribution to the swell of signature voices taking a momentary lead in this overture. The breathy fluting of two mothers follows, their calves piping piccolos close at their sides.
Suddenly, Monostatos’ metallic whirr cuts through the calls in this marine performance of The Magic Flute. A propeller’s percussive clack-clack-clack slicing through the water is the prelude to the low engine hum that drowns the voices of the group. With a start, I realise that it’s the boat moving closer to retrieve me from the water. I lose my bearings in relation to the group and although it is still nearby, I can’t locate it as easily as when I could hear it. The dolphins quickly outpace me and, even in this clear water, without their sonic cues to guide my gaze, I soon have to concede that I’ve lost them.
Acoustics guide marine life; it is sound that helps species navigate, hunt, hide from predators, find mates and communicate with each other. The ocean soundscape isn’t only made up of calls from different animals, but includes ambient levels of noise from crashing waves and ocean spray, rainfall, and bubbles that form and burst. Somewhere in this oceanic orchestra, the strains of human activities – commercial shipping, seismic exploration, the back-and-forth of recreational vessels – are increasingly heard and, in many cases, overpower the sea’s other voices. As the number and size of ships traversing the ocean has increased, explains John Hildebrand from the Scripps Institute for Oceanography in his 2009 paper for the journal Marine Ecology Progress Series, ambient ocean noise levels have risen by 12 decibels.
For the humans that are temporary visitors to the ocean’s depths, noise pollution is relatively inconsequential. My own survival, for instance, wasn’t linked to losing earshot of those dolphins on the day the inflatable boat purred over to collect me off the coast of Ponta Malongane. For many ocean animals, however, noise is the ironically silent pollutant in the oceans today, its insidious impacts less frequently discussed than those of plastic and oil spills.