Many of us are familiar with the evocative songs of the humpback whale, but it remains a mystery why all males in the same breeding group sing the same song throughout the season. This doesn't quite square with our common conception that male animals sing to advertise breeding fitness, a strategy that might be less ambiguously expressed if they all sang different songs. And why do they all change their songs every year?
We have known for some time that dolphins and porpoises use biosonar to sense their surroundings. Their high-frequency chirps and buzzes help them locate food, navigate during cooperative, high-speed hunting tactics and frolic in their surroundings. But we have only recently learned their biosonar can also let them "see" deeply into body tissues and identify extremely fine details in their environment.
There is informed speculation that baleen whales' low-frequency vocalizations are also a form of biosonar. They may be using long-wavelength sounds to navigate across large expanses of water — projecting these sounds a thousand miles over the horizon to bounce back to them off seamounts, trenches and continental shelves as long-distance echolocation.
In chorusing, whales, fish and marine invertebrates all sing in temporally coordinated vocalizations like crickets or frogs. Croakers (sciaenids) synchronize in acoustical "stadium waves" across 45 miles of coastal habitat, and minke whales chatter and pulse together across large expanses of open ocean. Even the whistling of barnacles carries some critical biological message that we may never decipher.
We know larval forms of reef animals imprint on the sounds of their "mother reef." When they are first conceived these tiny organisms are not served by remaining in their birth habitats, in which millions of mouths are seeking food. So in the early stages of life they disperse out into the pelagic zone to gain some heft. But once they are large enough (and often in a completely different shape than their larval form) they need to return to the reef to live. They find home by following the sounds they know from the first stages of their life. We know they do this, but we don't know how they imprint. In many cases we don't even know how they hear.
Sound works differently in water than in air. Water is much denser and is not compressible. This allows for a more efficient transfer of acoustical energy through water than through air. It is fairly easy to make a sound in water that can be heard a few thousand miles away; baleen whales do this all the time. Humans also do this all the time in water, but unlike whales that use these sounds for biological purposes, we do it for commercial, industrial and military purposes — often to the detriment of the sea animals.
Humans are a noisy species, and this is nowhere more evident than in the ocean. The impacts are becoming more apparent in the form of catastrophic marine-mammal strandings, compromised and depleted fisheries and high stress levels in animals that can lead to biological dysfunction. Because we know so little about how sea animals hear and what they do with sound, we have a very limited understanding of the impact of our noise.
In some cases the sounds we make might not be such a problem; the ocean with its crashing waves, grinding ice, pounding rains and billowing hydrothermal vents can be a noisy place, and animals have adapted and evolved to account for these sounds over the millennia. But the sounds we bring into the sea are quite different from these naturally occurring noises. Thus, we must learn how the din of our ocean enterprises affects the sea's inhabitants, or we risk creating an environment in which their survival is uncertain.
— Bob Talbot
© Alert Diver — Summer 2012
