to What Fish Tell Us
by Tracey Crago, WHOI Sea Grant
Rodney Rountree is an unabashed eavesdropper. He listens in on con-versations
as often as he can, sharing what hes heard with as many people
as he can. And he gets paid for it.
Rountree, a postdoctoral fellow at the University of Massachusetts
Dartmouth, is an expert in the field of soniferous fishesfish
Of the 150-plus East Coast U.S. fishes that make sounds, Rountree
has heard from a dozen or so and documented about half that number.
And while it may be relatively easy to listen to fish, its an
altogether different story when it comes to knowing what you are listening
to. That generally requires videotaping the fish.
most frequently at sunset and the hours just after," explains
Rountree. To get video, Rountree must use a camera with lights. This
causes some fish to avoid the camera, he says, and others to modify
their behavior. "We have trouble getting the fish to cooperate
and vocalize on camera," says Rountree. "Even if a fish
does vocalize on cue, its difficult to tell because, unlike
terrestrial animals, there are no obvious physical movements."
Rountree, aboard the R/V Connecticut, conducts passive acoustic
research at the Stellwagen Bank National Marine Sanctuary. A
hydrophone array, attached to an underwater video camera system,
monitors fish and their sounds. Photo credit: Rodney Rountree
Different species of fish use different mechanisms to vocalize. "Most
fish sounds are associated with the swim bladder, which acts as a
drum or an amplifier," says Rountree. Common examples are weakfish
and toadfish, fish that make sound by vibrating a muscle that is attached
to the swim bladder. The swim bladder then amplifies the sound.
Pharyngeal teeth, located in the throat of some fish, produce sound
when ground together. This sound is amplified by the swim bladder.
Even fish without swim bladders can produce sound, says Rountree.
Longhorn sculpin vibrate the bones of their pectoral girdle to produce
a humming sound. "You can actually feel the vibration in your
hand when you hold them," says Rountree.
To determine when, where, and why fish vocalize, Rountree uses a repertoire
of non-invasive sampling strategies. "The backyard science
method is a simple and inexpensive way to get basic biological, behavioral,
and spatial information," he says. It requires a hydrophone (the
$200 type) and a basic underwater camera.
To get a sense of spatial distributionwhat fish are in what
locationrequires simply going to a site, putting a hydrophone
in the water, and listening for well known fish sounds. "By recording
locations where you hearand dont heara particular
fish, you can plot a map of fish calling locations," says Rountree.
This method allowed Rountree to make an important discovery during
the summers of 2000 and 2001 while sampling for soniferous fishes
in Cape Cod waters on a project supported by WHOI Sea Grant. Rountree
observed and recorded an abundance of striped cusk-eels, Ophidion
marginatum, in Cape Cod estuaries and coastal waters. "This species
was previously thought to occur from New York to Florida, and only
as a rare stray to Cape Cod," explains Rountree. This finding
is significant, he says, because extensive sampling with conventional
gears, like seines and trawls, has failed to collect cusk-eels in
the area. "This demonstrates the usefulness of passive acoustics
as a tool to supplement other types of sampling in fish surveys,"
Once a good location for recording fish sounds has been identified,
vocal activity can be studied at that location by recording sounds
for longer periods at different times during the day. And, comparing
day and night samplings from one location can reveal when a fish is
most active. "The cusk-eel vocalizes sporadically throughout
the day and night," explains Rountree, "but around sunsetwhen
spawning takes placewe hear a chorus of cusk-eels representing
many individuals vocalizing at the same time."
The expensive part of the work, says Rountree, is the software required
for sophisticated analysis of the recordings and the cost of a technician
to do the analysis. For some of his research, Rountree uses a more
advanced hydrophone that costs about $1,500. In the near future Rountree
hopes to set up a fixed array of hydrophones in Buzzards Bay, just
outside his office.
"An array helps triangulate the sound," says Rountree. "We
can tell where the sounds are coming from. If the fish are vocalizing,"
he says, "the array can be used as a tracking tool: do they move
or stay in the same place, and where exactly do the fish spawn, for
So what causes fish to vocalize? Many, according to Rountree, vocalize
when spawning, although some, like the toadfish, have different sounds
for different behaviors. "A low whistle signifies a male calling
to a female. These sounds peak at sunset and often go on all night,"
he says. But toadfish also grunt in response to stress.
Haddock also vary their vocalizationspulses actuallysignifying
different stages of courtship. "To attract a female," explains
Rountree, "a male will make a regular and repetitive thump. If
he gets a response, the thumping will become faster, with different
spacing between thumps. During mating," he says, "they will
make a constant, drum roll sound."
For his WHOI Sea Grant work, Rountree has been making important connections
between fish sounds and the identification of essential fish habitat
(EFH). "When we record spawning sounds in certain locations,
we can make the connection that this is an area that is important
to spawn-ing. The catch," says Rountree, "is that it only
works for species that are vocal and for which you know the sounds."
In a related project, Rountree is working with MIT Sea Grants
Cliff Goudey to distribute archival fish recorders to fishermen to
aid in the collection of Gulf of Maine cod and haddock sounds. The
goal is to learn more about the location and timing (seasonal and
daily) associated with spawning and courtship.
Rountree says he and his colleagues who study soniferous fishes rely
on each other to help identify sounds they record. He is working with
colleagues in the U.S. and abroad to establish an archive of fish
sounds. A project based at Cornell University is currently underway
to create a systematic digital library of fish sounds, something that
will be useful to seasoned eavesdroppers like Rountree, and for the
up and comers who will add to the database.