Sounds from the Deep
Seventy per cent of the surface of the earth is covered by water. More significantly, the water is three dimensional, in that there’s far more to it than what we see at the surface. With light only penetrating the first 30 or so meters down, the vast majority of aquatic and marine ecosystems have evolved in darkness. The ample and diverse life forms that make these inky waters home depend on senses other than sight, but yet we know so little about how they manage. Here to help make sense of these watery worlds and the animals that make it their home is our regular environmental contributor and host of Blue Fish Radio, Lawrence Gunther.
(Transcript of Lawrence Gunther’s bi-weekly 12-minute segment on Live from Studio 5 broadcast over AMI TV and Audio across Canada)
Q. Welcome back Lawrence, why do most fish and other animals that live in the water have eyes when much of the water on earth is in darkness?
A. Fish that live in rivers and lakes and along the coastlines, and even those fish and animals that live far out from land, often still use their eyes to detect light or movement, just as do most of us including the 90 per cent of those who are registered as blind but who can still see a bit. All animals that live in the water experience complete darkness at least half the year. Every night when the sun goes down these animals are still active, and in many cases more-so. They just don’t depend on sight that much, and have instead developed far greater dependence on non-visual senses that are unrelated to light such as hearing.
Q. Fish must be able to see colour, because when you go into a fishing tackle store there sure are lots of different colour lures on display.
A. Whether fish can see colour or not is almost inconsequential. The properties of water filter colour out of light, with the colour red being the first to disappear at the depth of about three meters, and the colour blue being the last to go at around 30 meters. The different coloured lures are intended to represent the different colours and shapes of the food fish eat, but serve primarily to get anglers to bite and buy their products. What we are just now learning however, is that many fish can also see ultra-violet colours, which is a spectrum of light not visible to the human eye, but at the same time capable of being transmitted to depths of up to 100 meters and more.
Q. If aquatic and marine animals can’t depend on sight, what other senses do they rely on?
A. Smell is one. You often hear how sharks can detect a single drop of blood in the water from as much as a kilometer away. Taste is another, but with most fish like sharks their taste buds are outside of their mouths, which allows them to touch a potential food source with their face to determine if it’s a familiar food. Fish and other animals can also hear quite well, and even though they don’t have ear holes in their heads to let sound in, they’ve developed other ways to listen that are truly remarkable.
Q. How well can animals that live under water actually hear?
A. Thanks to the sound transmitting properties of water, fish can hear amazingly well. Next time your swimming, put your head underwater and listen. Everything sounds like it’s coming from inside your head. That’s because sound travels four times faster underwater than it does through the air. Our brains aren’t prepared to make sense of sound coming into our ears so quickly. Dolphins and killer wales actually bounce sound off objects like submarines use sonar to detect things in the water they can’t see. Large wales such as Blue Wales can articulate sounds like us, and their low frequency sounds can travel across entire oceans.