The not-so-silent seas

 kw: book reviews, nonfiction, science, oceanography, acoustics, bioacoustics, sound, noise pollution

A number of years ago at the beach at Cape Henlopen, Delaware, a pod of porpoises came by, a hundred yards or so offshore, as they usually do in the afternoon. This particular day a couple of busloads of Amish people from the Lancaster, PA area had been brought for a day at the beach, and I was standing about chest-deep in the water among a dozen or so Amish teenagers. As I like to do when the porpoises swim by, I ducked my head under water to listen to them whistle and chirp. It is a sound I love. I liken it to the social honking of a V of geese flying overhead.

I said to the nearest Amish boy, "Try putting your head under water. You'll hear the porpoises." He tried it, and then shouted something in German to the other kids. Soon they all were bobbing up and down and chattering among themselves about this novel experience.

As a teen I often watched the Flipper TV show, centered on a bottlenose dolphin (the "poster child" of porpoises). I was familiar with the chatty noises the animal could make. A few years later I was enthralled to listen to the album Songs of the Humpback Whale. As an avid reader of science articles and books, I've kept up in a general way with the findings of bioacoustics about the whole range of animals that make sounds under water, from snapping shrimp and mantis shrimp to the fish called Grunts—and many others that do more than grunt—to the mammals, particularly whales (I count porpoises as small whales).

The title Sing Like a Fish: How Sound Rules Life Under Water was a slam-dunk for me. The reading was as enjoyable as I'd anticipated. The author, Amorina Kingdon, muses in the Epilog whether it was worthwhile to devote two years of her life to the book and its research. She concludes a resounding Yes, and I agree. Who else could do this? Another might write on the same subject, but Ms Kingdon's voice is unique: heartfelt, lyrical and eloquent.

Early in the book we learn why we've ignored the underwater soundscape for so long. Our ears don't hear that well under water. In the age of sail, many sounds were heard by sailors trying to sleep below decks. When there is little wind, a sailing ship is so silent, the sounds of the sea that make their way through the wooden hull are quite evident. These days, professional sailors would be hard pressed to hear anything coming through the hull of a noisy, engine-driven ship. Those who never go to sea, who experience it only from above, have no idea how sound-filled it is. Early SCUBA divers, with Jacques Cousteau in the lead, hampered by air-adapted ears and the noisy SCUBA apparatus, heard so little that they produced a documentary film about the ocean titled The Silent World, about ten years before the first episode of Flipper aired. As I recall, the main sound heard under water in that film is the noise of the SCUBA. I wonder if Cousteau ever learned that fish have songs.

Although I wanted to learn SCUBA diving, I wasn't willing to pony up for expensive diving lessons and equipment. I snorkeled instead; I could surface dive to 40 feet without much trouble, and once went 60 feet. Snorkeling can also be noisy if you never leave the surface; we breathe rather loudly. But if you pop a surface dive down even 10 feet and just hang there, gradually the sounds will become evident. In my case, though, I dove offshore of tide pools, to see what animals were on the rocks. Most of the sound was wave noise, but I did hear a little of the fishy chorus around me: clicks, squeaks, and mournful groans. Better equipment has helped us realize that fish sing! Not just whales.

Once the hydrophone was invented, the soundscapes of the seas came into sharper focus (Hmm, bit of a mixed metaphor there; I guess you can figure it out anyway). Much of the book is devoted to surveying the breadth of underwater animal species that detect sound, hear sound (different senses), and communicate using sound. In one place it is stated that a catalog of fish sounds contained around 900 species. Compare that to the 94 species of cetaceans (whales of all varieties), all of which can vocalize. Though there are about 34,000 species of fish, the 900 "cataloged" to be vocal simply reflects the very early stage of "auditioning" the world's census of fish. I don't recall reading about any fish that were tested, that they were unconditionally silent, so perhaps I can fairly conclude that most, or nearly all, fish will be found to not just receive sound but to use it.

Certain invertebrates also make sounds intentionally. Snapping shrimp and mantis shrimp make noises loud enough to be weapons, though a mantis shrimp mainly relies on the fastest punch in the animal kingdom as its primary weapon. Considering the wide range of insects that make noises to communicate and court, it's reasonable to assume that many of the active invertebrates also use sound. I immediately thought of scallops, which make a clapping sound when fleeing danger, but in their case I think the sound is incidental to the "jet propulsion" their clapping produces.

Sadly, there is a new player on the soundscape. Us. Ship engines are noisy. The propellers ("screws") are noisier. Sonar is noisy. Seismic surveying is incredibly noisy. The racket of pile driving to install offshore wind turbines drives whales and fish crazy and can kill them. The low rumble of the turbines once they are operating is a chronic noise that drives migrating animals to change migration routes, and hinders the feeding activities of many animals that need to hear their prey. So does the persistent growl of ships' propellers and the hammering of depth-finding Sonar. A couple of chapters are devoted to describing all the problems that sea animals are having with the sounds we make while we use the oceans for commerce and entertainment.

The book ends on a hopeful note regarding the confluence of regulation and public attitudes that can result from wise use of scientific data being collected right now. We know we can't protect everything, but if we know certain areas that are most sensitive—such as a special bay where certain whales raise their calves—we can focus our efforts where they are more effective.

Just in case you're wondering: This sonogram illustrates why we call the sounds made by humpback whales "songs":

For reference, middle C on a piano has a frequency of 261 Hz. 200 on these diagrams would then be near the G below middle C, and it happens to be the natural frequency of my speaking voice. To sing along with this whale, just follow the lowest, darkest line of each group. The highest blip on the second track (~700 Hz) is almost an octave higher than the highest note I can sing, which is an A with a frequency of 440 Hz. Most women can just reach the next A at 880 Hz, so a woman can sing with this whale, but not even a low-voiced man can reach the low tones near 50 Hz seen in much of the second track. This whale has a very wide vocal range!

But why are these a song rather than tuneless noises such as some people make when concentrating on whittling or something similar? In a word, structure. Phrases and shorter elements (words?) repeat and are sometimes repeated with variations. There is something intentional going on. One verse of a typical popular (human) song lasts from half a minute to a minute. Most song tracks on your playlist are 3-4 minutes in length. A typical section (verse?) of a humpback song lasts a couple of minutes, and such verses are grouped into soliloquies lasting on average 8 minutes, but the whale may sing the song, over and over again, with variations, for an hour, or even a day. Maybe a whale is a philosopher, and this is his way (only males sing) of thinking out loud. Or maybe these are courting songs, which the whale will repeat until a female responds, perhaps from miles away, and joins him.

A book like this reminds us of what we don't know, and hints at the level of effort we'll need to exert to find out what the natural world contains, while it is still there. That's the author's aim. The fish are singing, for their own reasons. But now we are able to hear. Will we value their songs enough to preserve them, not just as recordings, but by preserving the singers?