Listening to Fish

Latest update August 22, 2019 Started on October 30, 2018

Join me, Dr. Rodney Rountree, A.K.A. “The Fish Listener” in my decades long quest to identify organisms that are responsible for an incredible diversity of unknown biological sounds in oceanic, estuarine, and freshwater habitats.

October 30, 2018
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In The Field

I got a new ROV! Just beginning to learn how to use it. I'm looking forward to using the ROV to observe fish behavior and sounds!


Post # 12.
Sounds from Vilano Beach, Florida

I just returned from a short vacation in St. Augustine, Florida, where I had a chance to record some sounds on our last night.

Tolomato River, Vilano Beach, Florida on 30 April 2019. Fishing pier on the Tolomato River As soon as I dropped the hydrophone in the water I was met with a cacophony of sounds, dominated by the boatwhistle call of the toadfish, Opsanus tau. Here is a short clip. Spectrogram of sounds recorded about 11 pm Listen Toadfish near the hydrophone produce the strong red to yellow bars at frequencies between 100-600 hz, while only the peak frequencies of 200-300 Hz appear for many toadfish farther away from the hydrophone. Sciaenids (various species in the drum family) and snapping shrimp occur at higher frequencies.

After some time, a small motorboat came up the river and passed by the pier. I was surprised to see an apparent response of the toadfish which seemed to stop calling as the boat passed. Unfortunately, sound files long enough to show this in context are too large to post online, so I provide a spectrogram of the noise over the long sequence, and short clips at representative times.

Spectrogram of approximately 15 minutes covering a period before, during, and after the boat passage. You can see the numerous toadfish calls (green vertical lines) before and after the boat and wake noise, but not during the boat noise. Spectrogram apparent boat noise effect on toadfish

Here the spectrogram is zoomed into the time period of the boat noise (about 1 minute 15 seconds), in which you can see only three nearby toadfish calls (others are in the background). Spectrogram of boat noise Listen to the boat noise

Compare that to a call rate of 9-14/minute for the nearby toadfish (many more are in the background) in the rest of the recordings. Spectrogram of the soundscape before the boat Listen to the sounds a few minutes before the boat arrives

Auditioning marine catfish

I was able to capture and audition three fish, two hardhead catfish, Ariopsis felis, and one gafftopsail catfish, Bagre marinus. Both species make similar sounds, and one of each species produced two different sounds during auditioning. I could feel the vibrations coming from different locations as I held the fish during auditioning. I was a bit shocked when I heard all three individuals calling while I was capturing them. In all my efforts over the years with many species, I've rarely heard fish call while fighting the line. Sounds are almost always heard only as you handle the fish.

Ariopsis felis Hardhead catfish, Ariopsis felis

Spectrogram hardhead catfish sounds The sound was filtered to highlight the catfish sound so the sounds of toadfish and others animals will be distorted when listening to the clip. Two types of sounds were produced by the specimen, the "normal" grunt, and a weaker higher frequency grunt labeled type 1 and 2, respectively. Listen to its sounds

Bagre marinus Gafftopsail catfish, Bagre marinus Gafftopsail catfish, Bagre marinus Spectrogram Gafftopsail catfish sounds

The sound was filtered to highlight the catfish sound so the sounds of toadfish and others animals will be distorted when listening to the clip. Listen to its sounds

Post # 11.
Sounds from the Amazon!

In the summer of 2012, I had the opportunity of joining an annual ecological survey of the Pacaya-Samiria National Reserve (PSNR) in Peru under the umbrella of Operation Wallacea.

PSNR is contained within the confluence of the Marañón and Ucayali Rivers where the main-stem of the Amazon River originates more than 3,000 km from the Atlantic Ocean. I stayed for 4 weeks at a base camp on the very remote Samaria River working from the historic riverboat, the R/V Rio Amazonas. Base Camp Base Camp on the R/V Rio Amazonas I observed, collected and recorded fish from a small dock located at the base camp, and from small motor boats and canoes from which we conducted twice-daily fishing surveys. Fishing with cane poles Dr. Reuven Yosef with his first Piranha Fishing with gill nets Alfredo with gill-net catches Although staying in the same location for four weeks might seem monotonous, it was amazing how much the sights changed daily. I was there during the low water season when the vast amounts of water recedes from the flooded forest and lakes. Flooded forest Flooded forest and lake in the distance Vegetation choking off river as it recedes River gets choked off with vegetation as the water recedes Because of this rapidly receding water, different species of fish would be forced to migrate out of the flood zone and down the river as their species tolerances were reached. For example, these photographs taken from on deck of the Rio Amazonas show some of the thousands of cory and doradid catfish, like the ones you may have in your home aquarium, migrating down the river. Cory catfish migration Cory catfish migrating down river Dorid catfish migration Cory catfish migrating down river

Below you can view a short movie clip of vast number of Palometa fish (multiple species) migrating out of the lake and forest and moving downstream.

Remember my post on fish fart and how many fishes need to gulp air at the surface (see post # 9)? Well that’s what all these migrating fishes are doing, though in this case I did not hear any evidence of FRTs or other air movement sounds.


When working at the base station, I was able to set up a fish holding and auditioning center right on the floating dock. I would first audition a specimen in a kiddy pool and then in the river by holding it gently under water near a hydrophone. However, I was only able to record here when the engines and electrical generators of the support ships were turned off (we had electricity for only 8 hours of the day, split between morning, noon, and night). So basically, in addition to participating on two surveys per day, I also got up at daybreak, and stayed up well after 10 pm, to record at the dock (not much sleep for me!).

Dock work station Dock auditioning station During the fishing surveys, I had to make do with auditioning in a small plastic tube and then in the river. All fish were released after auditioning Releasing fish

Piranha comparison

So far, we have measured and processed thousands of fish sounds from the auditioning and soundscape recordings. We recently published a comparison of Piranha sounds demonstrating the potential of passive acoustic monitoring of Piranha in the Amazon. My colleagues and I are now working to describe the soundscape of the study area. On of the interesting findings is the apparent strong impact of piranha feeding on the local fishes (hmm, ouch!) Listen to a recent Scientific American 60 second podcast: Podcast

Sample sounds For more information, and lots more sound samples, go to my web page at: The Amazon Soundscape

Platydoras armatulus Platydoras armatulusListen

Red Piranha, Pygocentrus nattereri Red PiranhaListen

Agamyxis pectinifrons Agamyxis pectinifronsListen

Post # 10.
Carolina Fish Sounds Over the years I have auditioned many fish for sound production while vacationing in North and South Carolina. Here are a few examples of fishes I've auditioned and those that I have recorded sounds from. One of my favorite places is the public fishing pier on Newport River off the Beaufort/Morehead City causeway. Rountree recording sounds in Beaufort, NC Another site was on a small marsh creek "Harbor River" on Harbor Island, SC Rountree recording sounds in Harbor Island, SC

When I'm recording in the field, I often try to do both "soundscape" recording of the environment and “auditioning” of individual fish. Soundscape recording is where I drop a hydrophone, and sometimes a camera, into the water and record all the sounds from the natural environment, which includes both biological sounds and noises made by man's activities such as boating and fishing. Unfortunately, we still know so little about fish sounds that many of the sounds I record are unknown. So, one way to address that is to audition fish at the same time and place where I am recording the soundscape. To audition fish, I hold individuals underwater in the habitat where it was caught and record any sounds it makes while I’m holding it near a hydrophone. If I can’t get to the water, the next best thing is to audition the fish in a container like a bucket or small pool. Rountree auditioning a sheepshead in Beaufort, NC

In recent years I record simultaneously from the hydrophone and a microphone to record both the underwater sounds and any voice notes or air-borne sounds. Voice notes are helpful for long-term archiving of the data and in case written notes are lost. I've learned the hard way not to rely solely on the voice notes as sometimes the microphone fails for various reasons (or there is too much noise to hear them clearly). I can see my old professors rolling their eyes the few times I've relied solely on voice notes. Didn't they teach me better in school! Sure enough, the recording failed! And you know that when a recording fails, it was of something important! Well in my defense I'm usually working by myself and it’s hard to take notes when you are trying to audition a wet, wiggling, fish, take pictures, get measurements, and record the sounds at the same time without getting your notes or equipment wet. Try doing that when its windy too! To learn more about methods of auditioning fish in the field, see my brief pictorial guide at: Guide to auditioning fish in the field

Photo of my Mom braving the cold to help me (and catch some fish for dinner!) in November 2011 Sometimes when I was vacationing in Morehead City, my Mom, who loved to fish, would accompany me. Unfortunately, she passed away a few years ago and I was taken by surprise when I heard her voice while reviewing these recordings in order to create this post (and a related page on my web site). The first time I noticed she was laughing at me while I struggled to hold a lizardfish in the auditioning pool! Have you ever tried to hold a lizardfish? They are very strong and almost as bad as trying to hold an American eel. Me trying to hold a lizard fish for auditioning on another occasion Listen to Mom tease me as I tried to audition a lizardfish

Usually when I'm sampling, I am inundated with questions from local fishermen and tourists, which can often be heard on the recordings. They are always fascinated, and then some of them start bringing me fish to audition. Sometimes it’s more than I can handle and I don't get to fish at all myself. But that's o.k. with me. In that way I've gotten to audition some fish that I would not have had an opportunity to audition if I had to rely on my own fishing ability! Below, listen to the sounds of some of the fishes I’ve recorded. For more examples see my web page at

Pigfish Pigfish spectrogram

Listen to the pigfish

An uncooperative searobin! Searobin spectrogram Listen to the searobin and me!

A very angry toadfish! Toadfish spectrogram

He bit me!

Pufferfish Pufferfish spectrogram

Listen to a pufferfish

Hey everyone, I hope to be down in Morehead City, NC to begin my field season in March and plan to do some recording. Let me know if you’d like to pay a visit to watch (usually in the late afternoon and early evening).

Hi Rodney - great looking project and research area. Do you ever leave any remote listening equipment underwater unattended to listen to the fish? If so, what do you use? Our project looks at nesting Black Bream and we are sure they vocalise but we have had trouble getting good recordings. The kit has to be remote and unattached to the surface given the tidal areas we work in, and the fish hide when divers are around. Ideally we want to film and record sound at the same time but the two systems don't need to be connected. Please follow our project to see how we get on this year. Thanks, Matt

Apologies for the multiple posts, the edit function does not work and I have to delete posts and re-do them from scratch to fix errors.

Post # 9. Fish Farts!

Indian Pond Sampling

There I was sitting alone at a boat landing on Indian Pond; a remote man-made reservoir at the headwaters of the Kennebec River just below Moosehead Lake. It was just before dark on 18 May 2008. It was so quiet I kept looking around to see if a bear or a moose was sneaking up on me. Maybe bigfoot? Then out of nowhere I heard the unmistakable sound of a fish fart!

Listen to what I heard:

I was amazed! If you were there, you would have heard me talking out loud trying to explain to Bigfoot how it was impossible for a fish fart to be heard in a remote lake in Maine. That’s because at the time I thought that the only fish that made fart sounds, formally known as “fast repetitive ticks” or “FRTs”, were the Pacific and Atlantic herrings (Clupea harengus and C. pallasi). Two teams of scientists, one from Canada and the other from Europe, had independently described the herring sounds just a few years before (2003). The idea that fish might use fart sounds for communication quickly caught on with the media and general public with radio and tv interviews. The scientists even won an Ig Noble award from the journal “Annals of Improbable Research” in 2004.

FRT sounds start with a broadband pulse of sound like “kkkch” followed by a series of tic or tap sounds that continue for a while with each new tic farther and farther apart. Here are examples of FRTs I recorded in Maine, the second one is the one I first heard in Indian Pond.

Examples of FRTs I recorded in Maine

Why did I think it was such a big deal to hear a fish fart sound in Indian Pond?

The problem was there were no herring anywhere near Indian Pond. In fact, there were no fish in the herring family at all in the lake. So how could I be hearing fish farts? Well I began to research the topic and found that the 2003 studies were not the first to describe this type of sound, but in fact, fish farts were among the first fish sounds to be reported in the scientific literature! As far back as 1857! They just were not called farts, but were referred to more “delicately” as air passage sounds. It turned out that fart sounds are just one of a wide range of sounds often called “air passage” or “pneumatic” sounds, and which I now term “air movement” sounds, because they involve air movement within a fish, or air passage from the anal vent, gills or mouth.

Needless to say, I was very excited by this discovery and Francis Juanes and I attempted to publish the findings many times. But our papers were rejected over and over because scientists just plain did not believe the fart sounds we reported were produced by fish, or if they did, they did not care because the prevailing wisdom was that these types of sounds are just incidental to physiological processes and therefore not important enough to study or publish. What they meant by “incidental” is that just like for us, when we burp or fart, its not a form of communication, but just a physical process. Hmm, maybe that’s not entirely true for kids!

Anyway, unless we could prove without doubt that the sounds were made by fish, and what the species were, we could not get our findings published. So, we set out to get the evidence we needed. Unfortunately, funding agencies were not interested in supporting our proposed research for similar reasons. At the time, there was simply not much interest in basic observational science, especially in freshwater habitats, and especially not for air movement sounds.

So, did we give up?

Of course not! We just went out and did it ourselves. Without funding, we had to work in our spare time and during trips of opportunity. It took ten years of hard work, but we did get our proof of air movement sounds in freshwater fishes throughout the region. We still don’t know what species produced the fart sound I heard in Indian Pond that day, but it was likely a trout or chub. In our follow-up work, we described the air movement sounds of five fishes, the alewife (present in the lower Kennebec River and other rivers, but not Indian Pond), brown trout, rainbow trout, brook trout, and the white sucker. We also described sounds that are most likely made by the Atlantic salmon. All these species occasionally produce FRT sounds, but more often produce other types of air movement sounds.

Rountree, R.A., F. Juanes, and M. Bolgan. 2018. Air movement sound production by alewife, white sucker, and four salmonid fishes suggests the phenomenon is widespread among freshwater fishes. PLoS ONE 13(9): e0204247.

What are air movement sounds?

Many fishes have a gas bladder in their body that functions in one or more ways depending on the species. In some fish the gas bladder is used like a lung for respiration, in others it is used for buoyancy control, and in some fishes it is used for sound production (like the cusk-eels I talked about in an earlier post). In more primitive fishes, there is a connection between the gas bladder and the digestive tract because the only way the fish has to fill or empty the gas bladder is to gulp air at the surface or release air through the anus, gills or mouth. These more primitive fishes are called “physostomous” fishes, while more advanced fishes that do not have the gut connection are called “physoclistous” fishes. Physoclistous fishes with a gas bladder can fill and deflate it by directly moving gas in and out of the blood stream through a special structure called the Reta mirabilia. Note that physostomous fishes are among the most diverse and numerous fishes on earth (for example, many of the freshwater fishes kept in aquariums are physostomous).

Often when you see a fish jump, or splash at the surface, that’s when it is gulping air to fill its gas bladder. At this time, they sometimes makes sounds as the gas is moved internally or vented through the anus, mouth or gills.

The first time I ever observed this behavior was just after dark on 30 April 2008 in a tributary of the Connecticut river. I saw a small fish jump and then a moment later heard it squeak. Here is a slide showing the frequency structure of the sound series (top colored section). The circled areas show the sound of the fish jumping and then its squeak. The color indicates how loud the sound is and the y-axis indicates the frequency of the sound. Chanel 1 (very top) is the underwater sound, and channel 2 is the sound from my dubbing microphone where you can also hear the sound of the jump (but not the squeaks) and the sound of my voice as I made notes.

Slide showing the jump and squeak spectrogram

Listen to what I heard

If the link does not work, go to the site directly. There is a space after "sound" that the web pages does not like. gallery/recording2008043020140126to45sclipfishjump_amp.mp3

I later documented this type of behavior in the alewife which I first heard in a tributary of the Kennebec River in Maine.

Alewife recording site in Maine

The alewife primarily makes sounds I call “coughs” as they expel air through their gills, but sometimes make a “pop” sound as an air bubble erupts from the mouth. They rarely make fart sounds but I have not yet been able to determine how (I’ve never seen air escape from the anal vent and suspect the sound is made by internal movements as Russian scientists have suggested for salmon).

Listen to the alewife “cough” sound

In the following video you can see several alewife (at half speed and amplified). One gulps air in a rapid burst to the surface in and then can be seen diving down from the upper right corner of the screen. If you watch closely you can see the bubbles released from the gills after each cough. A pop can be heard when it releases a large bubbles from its mouth at the end of the sequence.

Watch a video of river herring, alewife, sound production

Here is the sound that the white sucker makes after it gulps air at the surface. Unfortunately, I’ve never been able to capture it on video, but have observed it numerous times.

White sucker photographed on Cape Cod

Listen to the white sucker’s sounds: Finally, here is the sound made by a brown trout I recorded on Cape Cod. You will see one of the fish rise to the surface to gulp air in the upper right corner and then make sounds as it releases air from its gills.

Brown trout sound production

Based on our work, some of which is still to be published, we believe that air movement sounds are widespread among freshwater fishes (and probably marine fishes too). Although these types of sounds are likely incidental in many fishes, so few species have been studied that it’s premature to conclude that no fish use this type of sound for communication. In fact, there is already some circumstantial evidence that some fishes do use air movement sounds for communication. But even if not, we have shown that the sounds are unique to each species (so far studied), and therefore can be used in passive acoustic studies of those species. If you hear the alewife cough sound, for example, it pretty certain that at least one alewife is nearby. Thus, descriptions of this type of sound in fishes is very useful to scientists, resource managers, and conservationist, and is absolutely worthy of study and publication. We believe it is unfortunate that scientists have virtually ignored this behavior for so long and that we can learn a lot about fish by examining this behavior in other species.

Post # 8.
Sounds of the Hudson River

Hudson River Survey During the two summers of 2003 and 2004, my then undergraduate student Katie Anderson (now Burchard), conducted a survey of underwater sounds of the Hudson River, which was subsequently published (Soniferous fishes in the Hudson River. Transactions of the American Fisheries Society 137:(2):616-626). It was groundbreaking in many ways as it was the first study of biological sounds of the Hudson River, and one of the few soundscape surveys in freshwater habitats of North America. The study was funded by a Polgar Fellowship through the Hudson River Foundation.

Katie chose two primary survey sites that could not be more different from each other.

Pier 26 One site was located near the mouth of the Hudson River right on the docks of New York City, just a short way from the battery and within walking distance of the world trade center. The folks at The River Project let Katie deploy her recorder at their facility on Pier 26 The River Project.

Tivoli Bay The second site was in a very rural area of the Hudson River Valley 95 miles up-river. At that location the river was fully freshwater, but was still affected by the tides. The site was located within the Tivoli Bay National Estuarine Research Reserve near Red Hook, New York.

Nomad recorder What made this project possible, on our low budget, was that our friends at MIT Sea Grant, designed a portable recording system that could be left on site to record for up to three days. For you youngsters out there, this was state of the art, off-the-shelf technology at the time. A few early mp3 players were coming out, but recording mp3 files is not what we want because it compresses the file and provides poor quality audio. We needed files to be saved in *.wav format and to be able to control the sample rate. So, the recorder used a modified Nomad jukebox which had an amazing 10 GB of data storage! Wow! That was a lot then. We were a bit surprised but very lucky that we were able to set the recorder out on the dock in NYC, right within view (Katie tried to hide it around a pier cleat, but it was still visible) and no one ever stole it!

Katie recorded a lot of interesting sounds in both locations, but we still don’t know what made most of them to this day! To be honest, we did not really expect to record many biological sounds in the Hudson River at NYC. We figured it would be far too noisy. But amazingly things quieted down substantially after dark and the “city” came alive. We were only able to identify two of the fish sounds. Our old friends the striped cusk-eel and oyster toadfish were common, but usually in the distance. See my earlier post for cusk-eel sounds. Examples of toadfish sounds recorded by me on Cape cod:

oyster toadfish, Opsanus tau Sound of the oyster toadfish

Chorus of toadfish

As I said, most of the other biological sounds were unknown, and still are unknown. Imagine that! In the heart of the industrial world, NYC, we are still completely ignorant about the underwater soundscape and what organisms depend on sound for communication, foraging, predator avoidance, and orientation.

Here is an example of one of the many unknown sounds (note its best to use headphones to listen to these sounds, and you may want to turn the volume up, but be careful not to turn it too high): Unknown sound on the docks of New York City Listen to the unknown sound

The soundscape at Tivoli Bay was equally amazing. Of the many sounds recorded, we could only identify two, both were catfishes, the brown bullhead and the channel catfish. However, amazingly Francis Juanes and I were later able to prove that one of the unidentified sounds (ui-16t – “staccato”) was produced by the invasive freshwater drum which is now abundant in the Hudson River (a topic of a future post!).

Unknown sound later identified as of the freshwater drum listen to the unknown sound Katie recorded at Tivoli Bay that we later identified as freshwater drum

Katie and I posted many of the sounds, including some sounds of noises like cars and boats, on my web site. If you are curious, you can listen to some of them. Let us know if you figure out what any of them are!! Hudson River Survey

Post # 7.
First Fish Sound Survey in the Gulf of Maine Part 2. Silence of the fishes!!?

GOM Survey with ROV and ISIS

After our mixed experience in the fall cruise (see last post), we went back to the drawing board to rethink our survey strategy. The ROV was not an effective platform for our project, so attempting to locate soniferous fish using “null steering” was off the table. Fortunately, the NE-GL NURC center operated a different kind of platform called the “ISIS” which was basically a steel box frame on which were mounted several cameras, lasers, lights and other instruments. We thought it would make an ideal platform for our purposes. It was typically used in a mode where it drifts just above the sea floor to film benthic organisms and fishes. However, we thought it would be possible to set the system on the bottom.

We realized from our past experience that even at anchor, the ship would drift with the seas and pull up off the bottom anything tethered, so we planned to use a two-point anchoring method, where both bow and aft anchors are deployed to minimize ship movements. Normally the ship would maintain power and use its bow and aft side thrusters to maintain station when deploying instruments at a station, but that would be far too noisy for us to listen for fish sounds. That just goes to show you how little the effect of sound has been considered even by scientists in their efforts to understand the marine life. Most of the methodologies we use to monitor and study marine life produce a tremendous amount of noise. Both ships and instruments they deploy are noisy largely because the engineers that design them have not realized the huge problem noise can be.

The ISIS platform

Life gets in the way, again

After rethinking our approach, we were excited about the all-important spring cruise in the Gulf of Maine (GOM) when we expected to record cod, haddock and other fish sounds for the first time in North America. I had just completed a wonderful international workshop on how passive acoustics could be applied to fisheries issues in April 2002, that I organized with Tony Hawkins of the Aberdeen University and Cliff Goudey of MIT Sea Grant where I presented some of our earlier findings and talked about the GOM cruise to be conducted in just a couple weeks.

Listening to Fish Workship

Then the very next day I became ill and had to have emergency abdominal surgery. I was still in the hospital when the cruise date came so the cruise had to be canceled. I was the chief scientist and we did not have time to train someone to take my place. We were devastated. It was impossible for the NE-GL NURC program to give us a replacement cruise the following spring as we had hoped, but they did offer us a second fall survey in addition to our planned summer survey.

Still no fish sounds!!!

The ISIS system worked very well for us during the July and October surveys in 2002, we could not have hoped for a better system. Now that we were using the passive platform, we were no longer restricted to 8 hours of operation per day as with the ROV, so we were able to make much longer observations at all times of the day. It was not perfect, because even with this system, sometimes the ISIS would get dragged off station. Also, the noise from the ship’s generator was still a problem, as it was when using the ROV. But we were able to observe specific sites and even individual fish for long periods of up to hours. Many kinds of fishes were attracted to the baits on the ISIS.

Unfortunately, despite our best effort, we did observe fish sounds in either cruise. We saw lots of interactions, but no vocal displays. In the fall, we focused heavily on boulder reefs and made long observations of cusk, but never recorded another cusk sound. We are puzzled by the low incidence of fish sounds to this day.

Why so few sounds even when known vocal fish were competing for food? Was it because the fish were not vocal during the summer and fall? But we know from European studies that both cod and haddock can still make some sounds during the fall, though not the robust courtship calls that they make in the spring. Was it that even with just one generator, the ship produced too much noise? We doubt that as we did record the cusk in the first survey. However it could easily have masked sounds of fish farther away, or of fish like the longhorn sculpin that make very quiet sounds. But we had many instances of fish very close to the hydrophones competing for food, so that does not seem reasonable either. The equipment worked fine, because we heard many other types of sounds, like fish bumping into things or ripping bait from the chum bags. A puzzle indeed!

Some example videos from ISIS during the July and October 2002 Surveys:

In this first video, one cusk drives another one away from the bait. Here we might expect to hear some sounds, but do not. The three white bags in the image are chum bags holding the three kinds of bait (fish, clams, and crabs).

Cusk on Cusk competition

In this video, at least three cusk are present and feeding on the fish bait. There is no evidence of competition among them. We found that if cusk were in the vicinity of the ISIS when it was first deployed, they responded very quickly to the bait, and were only attracted to the fish. Never the clam or crabs.

Three cusk

In this video, a cusk is seen chasing away a haddock. Cusk were often aggressive toward other fish, especially if smaller, but tolerated larger cod and haddock.

Cusk on haddock interaction

In this silent video, swarms of hagfish and a single cod, were attracted to the fish chum attached to the ISIS.

cod and hagfish

A few other short clips from the cruise can be viewed on my web site at:

Post # 6.
First Fish Sound Survey in the Gulf of Maine Part 1. Adventures with an ROV

In the fall of 2001 my colleagues Francis Juanes (now at the University of Victoria, BC Canada) and Joe Blue (retired from the Office of Naval Research) and I got a small grant from the Northeast-Great Lakes National Undersea Research Center (NE-GL NURC) to conduct the first dedicated survey of fish sounds in the Gulf of Maine (GOM). Specifically, within the Stellwagen Bank National Marine Sanctuary.
Stellwagen Bank National Marine Sanctuary

Sampling area

We had two goals, first and foremost was to conduct a systematic survey to catalog fish sounds. Secondly, we planned to use advanced video and acoustic localization techniques to attempt to identify what fish were making sounds. In other words, to prove that a particular sound was produced by a particular fish. That is not always easy since its often not possible to determine just by visual inspection whether a fish makes a particular sound. Sounds recorded while a fish is in the field of view of a camera may in fact come from someplace else. So, we hoped to use triangulation of sounds on three hydrophones to determine if a sound came from a fish in the camera view or not. Since neither of these things had ever been done before, we were treading on new ground and trying to feel our way along.

Since no one had ever surveyed the GOM before (for fish sounds) we did not know what to expect. When and where should we sample? We had high expectations of recording a diverse array of different fish sounds based on our experience in estuarine waters on Cape Cod, New Jersey, North Carolina and Florida, and also on numerous studies in estuarine and coastal waters in the southeastern USA. We also knew that important GOM species like Atlantic cod and haddock had been recorded in captivity and in the field in European waters.

According to prior studies in the scientific literature, we expected that most soniferous fish vocalize at night during the spawning season. Therefore, we wanted to survey in different seasons, at different times of day and in different habitats to maximize our chances to record fish sounds. In the GOM, most of the important commercial fish that we were interested in spawn in the late winter and spring, some in the summer, but few fish spawn in the fall. The NE-GL NURC support ship did not operate at sea in the GOM during the winter due to harsh conditions, so we were limited to a one-week cruise in each of the other three seasons. However, due to the funding cycle and ship availability, we had to conduct our first cruise in the fall of 2001, which we expected to be the least interesting period. But then again, since no one had done this before, we did not know what to expect. Maybe lots of fish vocalize in the fall in northern waters? There was only one way to find out!

Rather than just conduct a survey by dropping a hydrophone over the side of the ship as had been done in European studies of cod and haddock, we planned to mount our hydrophones on a large ROV. Hydrophones were deployed on a Phantom III S2 ROV operated by the NE-GL NURC. The ROV would give us the capability of “looking” around for fish and places to record. But we also planned to use an array of three hydrophones mounted on the ROV in a “Cardioid” configuration designed by Joe Blue to use an old Naval technique of “Null steering” to home in on repeating sounds. The hydrophone array design would allow us to cancel out noise from the ROV and focus on sound coming from in front of the ROV. So, the plan was to sample four habitat types (sand, gravel, boulder and mud) at three different times of the day (noon, sunset, and evening). To reduce ship noise and maintain station at a site the ship was anchored and its engines shut down (except for one generator) during ROV dives.

Things don’t always go as planned

This project attempted many things for the first time and we were not experienced with the use of a large research grade ROV in the open ocean, so we quickly ran into some problems. Unfortunately, our acoustic and engineering expert, Joe Blue, was unable to participate. Second, due to the vagrancies of scientific funding, we did not receive acoustic equipment until just before the fall cruise so we did not have time to test and troubleshoot them. We quickly learned during tank testing right before the cruise that the Phantom III S2 ROV could not support the array in the forward position necessary to cancel out the noise. It had to be mounted right over the ROV body frame. That meant that the null steering option was off the table. We knew that the ROV could only be operated for 8 hours each day, and that we had to allow time for the pilot to sleep (no 24-hour sampling), but we did not realize that the ROV could only be deployed during ideal sea conditions, so we were only able to conduct less than half of the planned dives.

Deploying ROV

Other problems, were that the pilot would not fly the ROV without its lights and tracking system turned on. You see, ROVs are not designed to be operated without their thrusters on due to the risk of collision with the bottom or hard structure and damage to the system. And without the tracking pingers the pilot is flying virtually blind, something they don’t like to do! Besides the risk of hitting the bottom or some underwater obstacle, there is the risk of getting tangled in the ship’s anchor, or in the ROV’s own tether. With some practice the pilot was able to allow us to turn off the very noisy tracking system and lights for short periods with the ROV siting on the bottom or drifting just off the sea floor. But the current was too strong during many of the dives to do that.

As I said, in field research things don’t always go as planned, no matter how hard you try to prepare. But Francis and I were both experienced enough in the field to know that so we always have a plan B, C and D in our back pockets. Although we could not do the homing, we could use the ROV to search for fish at a site and then attempt to record sounds while the ROV was powered down and sitting on the bottom, or drifting just above the bottom. We also attempted to increase our chances of recording sound by attaching bait to the ROV in hopes of observing fish making sounds while competing for the food. To maximize our chances, we used three different kinds of bait to attract fish with different appetites, fresh chopped fish, chopped clams, and fresh chopped green crabs. We also planned to record under different lighting conditions: white lights on, infra-red lights only, and all lights off. That’s because some fish are attracted to lights, some avoid lights and as far as we knew at the time, fish could not see infra-red (IR) lights, which would allow us to film in the dark without disturbing them. However, we knew from previous experience in the laboratory and shallow water, that IR lights only allow us to see about two feet underwater.

So, what did we find?

We observed 17 species of fish as well as squid during the 10 (out of 24 planned) ROV dives conducted at 118 to 229 ft (36-70 m) depths. We observed fishes competing for food, fishes attracted to lights, avoidance of the ROV, and fishes following the ROV to feed on materials kicked up from the sand, or amphipods attracted to the lights.

Some example videos:

Spiny dogfish, Squalus acanthias, were frequently attracted to the ROV and were most common on the sand and gravel bottom habitats. We even had some problems when the sharks started chewing on the hydrophone cables! In this video the ROV is sitting on the sea floor on a sandy bottom with its engines shut down and the white lights on. The noise you hear is from the ship’s generators (the ship is anchored and shut down except for one generator to run the equipment). The thumping noise is from the ROV’s electronics. The loud thump at the end is the sound of the shark bumping into the ROV.

spiny dogfish shark hitting ROV

Ocean pout, Macrozoarces americanus, disturbed by the ROV. The loud screeching sound is the ROV thrusters, while the bumping sound is of the ROV touching the bottom as it follows the ocean pout. The two red lines are lasers from the ROV used to estimate fish size.

Ocean pout

Cod and haddock feeding on swarms of crustaceans (isopods and amphipods) that are attracted to the ROV lights after a few minutes of drifting . feeding frenzy

We were amazed and confused a bit, when after days at sea we had yet to hear any fish sounds despite all the opportunities. The ROV was clearly not the best platform for recording fish sounds, but still there were plenty of opportunities. Then toward the end of the week-long cruise, while the ROV sat on the bottom in a boulder field with only its IR lights on, we FINALLY heard some quite fish growls just before an adult cusk, Brosme brosme, entered the field of view. We were able to use acoustic localization to determine that the sounds came from somewhere within a few feet of the ROV and that the Cusk was mostly likely the fish making the growling sounds, which were heard only in the dark on this one dive. You can see how limited the visibility is with the IR lights and how the cusk sounds can barely be heard over the noise of the ship’s generator.
Note, the cusk is related to cod and is very different from the “cusk-eel” I described in an earlier post.

In this short clip you will hear a faint series of knocks or growls at the beginning, then after a moment you will see the ROV’s tether drifting into the view (one reason the ROV pilot is very nervous about operating without lights, thruster power and the tracking system!), and then you will see a beautiful cusk move into the field of view before turning and moving off.

Cusk at ROV

A few other short clips from the cruise can be viewed on my web site at:

*So, what did we accomplish? *

1) We conducted the first passive acoustic survey for fishes in the Gulf of Maine 2) We found surprisingly few fish sounds. We had expected fewer sounds in the fall season, but had hoped to record aggressive sounds of fishes competing for the bait. 3) We published the first description of the sounds made by the cusk; an important species that is of special concern due to its drastically declining numbers. 4) In our publication, we also described the noise characteristics of the ROV and discussed the potential bias of using ROVs to conduct video census of fishes because of their potential attraction or avoidance of the noise. ROVs are extensively used to conduct fish and invertebrate census in many kinds of habitats around the world. Lots of studies had looked at the light problems, but this was the first to suggest that the ROV’s noise might be a significant issue. 5) We concluded that although the ROV could be used for passive acoustic studies under some situations, specially designed ROV’s would be needed to make a ROV a good choice for passive acoustic surveys.

On to plan D….

The amazing enigmatic cusk-eel
One of the first fish species I wanted to record in the field was the striped cusk-eel, Ophidion marginatum. By chance, I had recorded their sounds with Jeanette Bowers back in 1989 while I was working on my Ph.D at Rutgers University in New Jersey. We had captured several individuals and were keeping them in the laboratory to try and spawn them, which had never been done before. In the laboratory the Cusk-eels tend to stay buried under the sand during the day and only came out to forage at night. male cusk-eel still partially buried in the sand

We noticed that male cusk-eels started calling with a loud “jack-hammer” or “woodpecker” sound at sunset as they tried to attract females in the tank. We did not have fancy equipment back then so we recorded the cusk-eel sounds with an old-fashioned desk-top tape recorder and used dim flashlights to observe the cusk-eel’s behavior in the dark.

Listen to the cusk-eel recorded in 1989

Amazingly the cusk-eels spawned every night for over a month and produced an unusual floating gelatinous egg mass. See photos:

photo of striped cusk-eel spawning photo of striped cusk-eel egg mass

A video taken during the 1989 study with a regular camcorder shows the typical spawning behavior of the cusk-eel (sorry its silent as the audio was lost). Note, it was difficult to capture the behavior on film because the species spawns at night and immediately burrows if disturbed or exposed to light.

Striped cusk-eel spawning in the laboratory 1989

Burrowing behavior of the striped cusk-eel, Ophidion marginatum, recorded by my student Katie Anderson about circa 2003.

striped cusk-eel burrowing behavior

As I mentioned in an earlier post, when I became interested in conducting studies of fish sounds in the wild, I was traveling from my home on Cape Cod to the Rutgers Marine Field Station in southern New Jersey (where I did my Ph.D.) to record cusk-eels and other fishes.

You can hear their sounds in the field recording I put up in an earlier post (here it is again):

My first attempt to record underwater video with underwater sounds

Little did I know that I could record them within minutes of my home instead of making the long trip to New Jersey! That’s because cusk-eels were not known to be present on the Cape Cod except as very rare stragglers from the south. Then one night I happened to be recording at sunset and there they were, as clear as day. Cusk-eels! I subsequently found they could be found all over the cape, including in Cape Cod Bay. That was totally unexpected. When I told colleagues about this, they assumed that cusk-eels were only recent visitors to the cape due to warmer waters. However, I discovered archival recordings from the early 1950’s in Woods Hole harbor with lots of cusk-eel sounds, so I believe they have always been here (though its likely that they invaded Cape Cod Bay only after the construction of the Cape Cod Canal in 1914). In fact, I subsequently found that the sound had been recorded in Rhode Island but mistaken for another fish. It was only after Jeanette and I recorded cusk-eel sounds in the laboratory that the mistake was discovered. These findings were important because it demonstrated the powerful potential of passive acoustics for fisheries, since here we were in one of the most intensively studied areas of the world due to the presence of numerous research institutions like the Woods Hole Oceanographic Institute, Marine Biological Laboratory, and Northeast Fisheries Science Center in Woods Hole, but no one knew that cusk-eels were not only present, but abundant! Word quickly caught on with the public and I began to be contacted by sailors and fishermen in the region exclaiming that they had been hearing the sounds for years. Normally underwater sounds from fish and other organisms are not audible above water because the water surface acts like a mirror and deflects the sounds back down. However, sailors sleeping below deck in sailboats for generations have heard strange underwater sounds because the sounds can pass right through the hull of the boat. On long-time sailor from Block Island published an article in a popular yachting magazine calling it “chatterfish” and describing how they always imagined it to be some kind of sea monster, or at least something really big. Funny it turned out to be the little cusk-eel which is less than ten inches long!

Listen to the sound of a cusk-eel

Listen to a chorus of many cusk-eels and also some toadfish

I did my best to publicize these early discoveries and educate the public and fisheries scientists about the potential importance of fish sounds to marine ecology and fisheries. The idea quickly caught on with the public, especially with kids who were fascinated by the thought that fish made sounds. Fisheries scientists were much slower to catch on to the potential. Over the years I have been interviewed by many reporters for newspapers, magazines, radio and online programs. One of the very first was an interview for Discover Magazine, and I was very excited about the publicity of my new avenue of research. I was a bit surprised, though delighted, when instead of an article the magazine published a poem by Josie Glausiusz in the January 2002 issue.

The Rime of the Modern Mariner

So I have the distinction of being the only one of my peers to be honored in poem published in a national magazine! My mom loved to brag on that to her friends for years.

Opportunistic recordings while on vacation!
Ever since I began recording underwater sounds in the wild 18 years ago, I have tried to bring my hydrophone and sometimes a video camera along with me whenever I travel. My first such adventure was when my family and I vacationed on Conch Key in Florida in April 2001. Much to my wife’s dismay, I put an underwater camera and hydrophone off a dock outside our bedroom window and ran the cables through the window and plugged them into the apartment’s TV and VCR for recording. We listened to the constant boatwhistle sounds of toadfish all night! Here is an example of the boatwhisle call of Opsanus beta

The clear water of the Florida Keys made for much better video recording during the day, but again at night everything goes dark and even with infra-red lights the video is useless (except for the sounds). Here is a short video clip of fishes hanging around the dock. The resolution of the digitized clip is still very poor. A toadfish can be heard at the beginning of the clip and then a parrotfish can be seen and heard biting on a concrete slab in the middle of the view at about 4 seconds. Other fish sounds can be heard toward the end of the clip. When I first observed the sounds of parrotfish bites, I immediately had the idea that passive acoustic monitoring could be used to monitor feeding behavior of parrotfish and other fishes on coral reefs, and perhaps to quantify bioturbation rates. You could easily count the number of bites per minute. I later learned that Thomas Bright had made similar observations during the Tektite project almost 50 years ago. Unfortunately, as far as I know, no one has yet attempted to use passive acoustics in this way. Video of Parrotfish bites with sounds In the video, the first thing you hear is the toadfish sound. Then at about 4 seconds you can see and a parrotfish in the foreground biting on a concrete slab. Later you can hear some other fish sounds.

Early days excitement and frustrations

My first attempt to record fish sounds in the wild back in August 2000 was a lesson for a very naïve scientist. I had obtained an inexpensive hydrophone but had no way to record sounds in the field. Of course, I wanted to get video recordings too so that I could identify what was making the sounds. Sounds simple? Not so much. It turned out that it was difficult to get cameras that accept an audio input from an external source. But even cameras with an audio input port were difficult to use because a special port had to be built into the underwater housing to allow the hydrophone cable to be plugged in. On top of that standard camcorders had very limited battery life and almost always had automatic audio gain which could not be disabled. Finally, even if those problems were overcome, the camcorder functions could not be controlled remotely while underwater.

I finally hit on the solution of using a standard VCR to simultaneously record sounds from the hydrophone and video from a recreational drop camera to a VHS tape. With that I could get up to 6 hours of recording time. But supplying power to the VCR in the field was a problem. I ended up using an AC-to-DC power inverter and a 12-volt car battery. Unfortunately, inexpensive inverters are electrically noisy and introduce a 60-cycle hum into the audio recording which is less than desirable. The VHS had to be protected from the elements, so I put it in a plastic box. This was the beginning of many a headache due to my use of equipment not designed for the field (and too many cables and adapters!). The other problem was that VHS is analog, it records decent quality audio, but has to be played back into a computer to capture the sounds and/or video in digital form. So right off the bat processing time is doubled.

Over the years I have frequently approached video camera and hydrophone manufacturers to encourage them to provide a system better suited to capturing both underwater video and audio. Unfortunately, the video people never want to deal with audio and visa versa. Early on I did find someone that would build a custom camera system – for $40,000, way beyond my budget! Things have not changed much since those early days and underwater video cameras with integrated hydrophone input are only available as expensive custom made units. Fortunately, my student at the University of Victoria, Xavier Mouy, is developing a low-cost underwater video system that will allow simultaneous recording of video and audio input from multiple hydrophones. See his OpenExplorer expedition at: The Fish Sound Project: Unraveling the identity of fish sounds in British Columbia, Canada

Equipped with my make-shift underwater recording system I set out to record my first underwater sounds with video on 5 August 2000 in Great Bay, New Jersey. What a disappointment! Although the system worked fairly well for recording the underwater sounds (except for the frequent DC hum), I quickly learned that recording underwater video in turbid water at any time of the day, let alone at night, is very difficult. Video quality is very poor due to limited visibility, low camera resolution, and low resolution digitizing of the video. A short clip from that first recording session reveals just how bad it was. The use of white camera lights only made the recording worse, and red and infra-red lights available on some cameras allowed me to see only inches into the dark water at night. A particularly frustrating problem was my inability to control the field of view of the drop cameras, so that the view was always moving and rarely looked in the direction I was interested in. My first attempt to record underwater video with underwater sounds

I soon began experimenting with numerous methods of mounting the camera on platforms to stabilize its field of view. I reasoned that since fish competing for food would be more likely to vocalize, that I should be able to document sound of fish attracted to baits placed in front of the camera. Still visibility and poor recording resolution, together with limited control of the camera field of view, resulted in very disappointing videos. Here is an example of a recording of fish attracted to a chum can deployed at night from a dock in Cotuit Bay on Cape Cod, MA on 30 September 2000. In the video you can see a scup, Stenotomus chrysops, black sea bass, Centropristis striata, and a large tautog, Tautoga onitis. In the first few seconds you will see a scup pulling bait from a chum can. You can also hear it tear the bait out and chew on it. The loud splash you hear is my fishing line hitting the water (You can easily hear fishing lines hit the water from several hundred feet away. Even in very noisy conditions.) Next you will see two small black sea bass feeding on scrapes left by the scup. One of the black sea bass leaves while one stays behind trying to get more food from the can (he is on the bottom near the left end of the chum can). The second sea bass darts away rapidly when disturbed by an unknown sound. Did you spot the tautog yet? Believe it or not, a large tautog is in the field of view during the entire clip! He is sitting on the left side of the screen facing the chum can. His head is larger than the height of the can (4-5 inches). You can see him move away in response to the unknown sound at the same time as the black sea bass. Video recording of fish attracted to chum

Boy did I wish I had an ROV to capture the video! Unfortunately, this was the basic system I had to use for a number of years.

Next up: Opportunistic recordings while on vacation!


Introduction to passive acoustics monitoring
“Passive acoustics is a rapidly emerging field of marine biology that until recently has received little attention from fisheries scientists and managers. In its simplest form, it is the act of listening to the sounds made by fishes and using that information as an aid to locating fish so that their habitat requirements and behaviors can be studied.” Rountree, R.A., R.G. Gilmore, C.A. Goudey, A.D. Hawkins, J. Luczkovich, and D.A. Mann. 2006. Listening to Fish: Applications of Passive Acoustics to Fisheries Science. Fisheries 31(9):433-446

Soniferous (= Vocal) fishes use sound for communication in much the way that frogs and birds do:

  • To advertise for a mate
  • In their courtship displays
  • To defend territories
  • As a predator alarm or disturbance call

So why do we care?

  • By listening to fish we can learn a lot about their behavior and ecology without killing them or disturbing their habitat.
  • Aquatic habitats are increasingly disturbed by human noise with unknown ecological consequences.
  • Preservation of the natural soundscape is important if we want to preserve truly natural habitats

How do fish make sound?

  • Stridulation – rubbing or scrapping together of fins, bones, or teeth. Example: Sailfin Catfish, Pterygoplichthys pardalis, recorded in Peru

Listen the sailfin catfish

  • Drumming – special muscles push or pull on an internal air filled organ called the swim bladder Example: Searobin, Prionotus evolans, recorded on Cape Cod

Listen to the searobin

*Air movement – little understood internal movement of air, or escape of air through mouth, gills, or anus (i.e., burps and farts)

Watch a video of river herring, alewife, sound production

Expedition Background

Ever since I first set out a hydrophone on August 5, 2000 in Great Bay, New Jersey (near the Rutgers University Marine Field Station,, I have marveled at the amazing diversity of underwater sounds, but was incredulous to learn that few sounds were known to science! One of my first endeavors was to track down and rescue historic records of fish sounds made by Marie Fish and her colleagues at the University of Rhode Island starting in the late 1940’s through the 1960’s and culminating in her book “Sounds of western North Atlantic fishes” published in 1970. I was successful in recovering the recordings which can now be obtained online through and through The Macaulay Library at the Cornell Lab of Ornithology ( Unfortunately, even this catalog of sounds is extremely limited, but amazingly it is still the most comprehensive catalog available today! Since that time, I have recorded fish sounds in estuaries from Florida to Maine, in the commercial cod and haddock fishing grounds in the oceanic waters off New England, and in the deep sea off of New England and British Columbia. I have also recorded extensively in many freshwater habitats including ponds, lakes, brooks, streams and rivers throughout New England, in the Zion and Grand Staircase-Escalante National Parks in Utah, and even in the remote Amazonian region of Peru. But everywhere I go, I find that most underwater sounds are unknown.

Why do we know so little about the underwater sounds of fishes and invertebrates? Basically, because our society has not been interested and scientific funding agencies are reluctant to support the necessary descriptive studies needed to document sounds. Basic alpha level descriptive science has become passé and the scientific community has largely lost its appetite for conducting the long-term, tedious, detailed work needed to describe thousands of sounds and the associated behavior of organisms that produce them, in favor of “quick” science methods such as what’s now called “ecoacoustic indices”. So what’s the solution? I have always maintained that people are fascinated by the underwater world, but simply lack exposure to it. I’d like a dollar for every time even scientists have exclaimed “I didn’t know fish made sounds!” when I’ve discussed the issue at conferences and scientific gatherings. Therefore, I’ve worked to educate the public on the topic throughout my career through my web page, public seminars, and popular lay materials like my free online children’s book “Listening to Fish: New Discoveries in Science” and popular fish song ringtones. I have always maintained that passive acoustics is ideal for “backyard science” efforts by laymen and should be part of every school’s biology curricula. That’s what prompted me to develop this OceanExplorer Expedition. In its pages I will highlight some of my past research efforts, and invite readers to follow along on my new adventures. I hope to occasionally provide opportunities for the public to join me for a day (or evening) in the field so they can experience the thrill of listening to known and unknown sounds with me. I also hope to encourage amateur “fish listeners” to conduct their own recordings and share them with me and all my expedition followers, so I will be providing tips on how readers can conduct their own projects.


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