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Perfect Place, Perfect Way to Learn About the Bay

Fish that Sing, Moan, Croak, Clatter, Drum... and Communicate

Rodenhausen holding croakerIt was a hot, hazy afternoon, and I was fishing in the Chesapeake Bay east of Annapolis.

At the wheel of the boat was John Rodenhausen, a skilled angler and captain who is Maryland Director of Development for the Chesapeake Bay Foundation. He used a sonar system to guide us over an oyster reef at Tolly Point.  He suspected the reef’s contours and crannies would shelter a multitude of fish and crabs.

“Look at the fish finder!” he proclaimed. “Look how many fish are down there right now!”

We slipped bloodworms onto our hooks, setting two per line, and cast into about 18 feet of water.  Within about 30 seconds, I felt tugging and reeled in pair of Atlantic croaker, each about nine inches long.

“Hey!  See, here we go! We caught a couple croaker,” Rodenhausen said, examining the fish as I gently removed the hooks.   “See, it’s got a downturned mouth, so he can feed on those mollusks and worms and little critters down on the bottom.”

From the fish rose a sound like a bullfrog singing. Urrrrrup! Urrrrup! Urrrup!  “He’s croaking away!” Rodenhausen said. I did not know fish could talk.

(To hear the sounds, listen to my radio program on the subject).

Perhaps the fish was saying: Let me go!  So I told the fish I would free both him and his friend. And I tossed them back into the water.  Plop.

It was an unusual conversation -- for me, at least.  But not that uncommon for the croaker.  As it turns out, croaker are one of several species of fish that routinely communicate by turning their swim bladders into musical instruments.

Back on shore, I visited the website of the University of Rhode Island’s website called Discovery of Sounds in the Sea and learned about a few other underwater conversationalists.

Oyster toadfish pictureThere’s the oyster toadfish (left), which makes a sound like a moaning ape.

There are weakfish (right), which sound like someone just jammed a chopstick into an electric fan. Weakfish

 
  Plainfin midshipman picturePlainfin midshipmen (left)-– although not large -- make deep hooting noises like a ship’s horn.

And then there are red drum (below), which sound –- appropriately enough -– like someone tapping their fingers on the head of a large African drum.  Red rum are so numerous in the Chesapeake Bay this year that some biologists believe they are gobbling up large numbers of baby blue crabs.
 
Red drumAfter listening to these sounds, the question I had was:  What biological purpose could this underwater noise-making serve? Do fish have languages?
 
“Croaker, like a lot of other fish, use sound in a variety of different ways,” said Arthur Popper, Professor of Biology at the University of Maryland and expert on marine bio-acoustics (fish sounds and hearing).
 
“Some use sound for mating.  Males will call the females. Or they may be using it for territorial behavior, to say ‘Get out of here, it’s my area, don’t bother me,’ Popper said. “Or they may be using the sounds for antagonistic interactions, for fighting.  They use sounds for all different kinds of things – just like other animals. Birds and other mammals make sounds. Fish make sounds and use sounds to communicate.”
 
Language would be too strong a word, Popper said, because each fish make sounds that convey only a handful of different signals -– compared to the millions of different ideas carried in human language.
 
Communicating by sound is especially important to deep-sea fish, Popper said, because they live in areas that are so dark eyes are almost useless.
 
So fish sing, moan, clatter, and chat.  But interestingly, fish do not have ears – on the outside of their heads, at least.  Their ear bones –  called otoliths – are inside their brain cavities. The fish hear by registering vibrations that pass through the water and impact the bodies of the fish, Popper said.
 
Popper said that noise pollution – caused by boat engines, Jet Skiis, and  marine construction– can hurt fish reproduction and survival by interfering with their ability to locate mates, prey, and predators.
 
“One of my concerns is what is happening in the Chesapeake Bay,” Popper said.  “As we increase shipping in the Chesapeake Bay, or pleasure boating, the Bay is getting louder.”
 
The sound of civilization washes through bays and oceans. Let’s not drown out the voices beneath the waves.
 
By Tom Pelton

Chesapeake Bay Foundation

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Photo at top by author.  Pictures of toadfish, weakfish, and plainfin midshipman from University of Rhode Island Discovery of Sounds in the Sea website.  Photo of red drum from Virginia Institute of Marine Science website, by Ken Neill of his wife Tricia Neill holding a red drum.

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