In my last post, we left off our acoustics 101 with the emergence of the first modern echosounders in the 1990s. Today, we will look at the current system aboard Oscar Dyson and learn how the science team can use their knowledge of acoustics to estimate fish populations. First, let’s look at the physical components that make up the EK80 echosounder system.
Each frequency requires its own transceiver. These six transceivers are the heart of the EK80 echosounder.
Transceiver – a combination of a transmitter and a receiver; in other words, it both produces an electrical pulse to be sent to the transducer and converts the backscattered signal into usable data a computer can understand. You can think of the transceiver as the electronic brain that manages all of the signal inputs and outputs.
Transducer – Just like you might plug a microphone into your laptop to record audio, each transceiver needs a transducer to first convert the electrical pulse into an acoustic pulse that is transmitted into the water, and to measure the acoustic backscatter that returns. You can actually see the transducers in the photo of the centerboard below. The transceivers measure frequencies ranging from 18 kHz (those really annoying mosquito ringtones that only young people can hear are around 18 kHz) to 330 kHz.
The red circles on the bottom of the centerboard are the faces of the transducers. These sensitive instruments are mounted at the lowest point of the ship to isolate them from the vessel’s noisy hull. (Photo credit: NOAA)
The Echogram
Once the transceivers process the acoustic backscatter, the data is displayed on a screen for interpretation.
There’s quite a lot going on here! Let’s break it down into smaller pieces so we can learn to look at the data like a scientist.Each of the six frequencies appears as a vertical section that scrolls from right to left as the vessel moves. The top of each plot represents the ocean surface, and the thick red layer near the bottom shows the seafloor. The space in between lets us look at what is below the ship! Weak backscatter appears blue; stronger backscatter appears yellow and even red.
Our old friend munge is making an appearance in this echogram! It is the heavy backscatter layer just beneath the surface that is strongest at 18 kHz. Lower in the water column, we see that most backscatter occurs at higher frequencies, with only sparse backscatter in the lower-frequency plots. Backscatter that is observed only at higher frequencies indicates smaller organisms, such as krill or copepods. Backscatter that appears across all frequencies is likely generated by fish.
As you spend more time looking at this scrolling echogram, you can begin to recognize patterns and draw reasonable inferences. Below are some examples of the variety you can see in just a few hours in the cave.
Younger pollock can gather in schools 20-40 meters tall that appear as very thin red ellipses.You can clearly see occasional reflectors on the 18 & 38 kHz channels; these may well correspond to adult fish. The only way to be certain is to trawl in an area that looks like this and see what the net brings up!We know that large fish like pollock return a relatively even acoustic signal across every channel that we look at; there do not appear to be any significant pelagic fish present in this echogram.
Now that we can read echograms, we are ready to call for our first trawl! Come back next time to see what we data we can scoop up in “The Anatomy of a Midwater Trawl”.
Personal Log
Things aboard Oscar Dyson have settled into a routine. We travel along acoustic transects during daylight hours, stopping 2-3 times a day to do a midwater trawl. Routine doesn’t mean boring, though! Maintaining a ship of this size and complexity is more than enough to keep everyone busy. The checklist for this leg included checking on the smaller craft that service and support Oscar Dyson on her mission. Conditions cleared on 06/29, and the Peggy D, the workboat that lives on the starboard hero deck, was given a thorough check and taken for a 30-minute voyage.
Peggy D secured to the aft hero deck of Oscar Dyson. ENG Connor Rauch and ENG Chelsea Gostomski on the aft deck of Peggy D.LCDR LeeAnn Keener and I enjoying the scenery.Bosun Alex Steele instructs me in the safe operation of Peggy D.
Safety drills and practice are a part of the routine as well. ENGR Connor Rauch practices recovery during a man-overboard drill on Peggy D. In the case of an actual man overboard, the smaller vessels are used for recovery, as they can respond much more nimbly and are far safer in close quarters with a swimmer.
Wildlife
This smooth lumpsucker (Aptocyclus ventricosus) is just as surprised to see me as I am to see him.Lumpsuckers have a unique feature: a ventral suction disk that allows them to firmly attach themselves to rocks in rough conditions.
NOAA Teacher at Sea Nick Lee Aboard NOAA Ship Oscar Dyson June 29 – July 20, 2024
Mission: Pollock Acoustic-Trawl Survey
Geographic Area of Cruise: Eastern Bering Sea
Date: July 10, 2024
Weather Data from the Bridge:
Latitude: 50° 40.9 N
Longitude: 178° 29.9 W
Wind Speed: 20 knots
Air Temperature: 6.2° Celsius (43.1° Fahrenheit)
Science and Technology Log:
Last blog post, I talked about acoustic backscatter, which scientists on board use to locate fish. When scientists notice high-intensity backscatter – or backscatter that they’re interested in collecting more biological data about – they’ll call the bridge and ask to go fishing. The bridge then makes the announcement over the radio:
“All stations. This is the bridge. We will be fishing, fishing, fishing.”
This announcement sparks a flurry of action from scientists, NOAA officers, and the deck crew. A few scientists go up to the bridge for a marine mammal watch, where they make sure that there are no marine mammals in the area of the operation. NOAA officers navigate to the science team’s target fishing area, and the deck crew prepares the net to go in the water.
Marine mammal watch on the bridge.
Before my cruise, I thought fishing nets were relatively simple and uniform. However, I’ve since learned that the net has many different components and sensors, which help scientists collect additional information about the fish seen with acoustics.
Codend
During the trawl, the net is dragged behind the boat. Near the opening at the mouth of the net, the net’s mesh is over a meter wide. This helps reduce drag from the water, while still funneling fish toward the back of the net. The net gradually gets smaller until the very end of the net – called the codend – where the fish are collected.At the end of each trawl, the net is hauled out of the water, and the contents of the codend are emptied into a sorting table for further processing in the fish lab, where length, weight, sex, and maturity are recorded for a representative sample.
Lowering the codend into the water at the start of a trawl.
Pocket Nets
In portions of the net with larger mesh, small fish and other organisms can escape through the holes in the mesh. This creates a problem for scientists – a trawl could show that only adult pollock are present in a certain area when in reality the population is mixed, but all of the juveniles escaped! Since scientists will be using trawl samples to understand the overall population of pollock, they want to avoid bias as much as possible in their data.
Pocket nets are fine black mesh on the side of the net made out of the same material as the codend, and they capture organisms that would have otherwise escaped.
To get around this problem, scientists are studying the rates at which different sized pollock (and other organisms) escape from the net. They use pocket nets, or small nets made of the same fine mesh as the codend, to get an idea of what escaped from each trawl. Nine pocket nets are attached to the side, top, and bottom of three different sections of the net with varying mesh sizes. As the trawl net is being hauled back on the boat, one of my jobs is to help empty these pocket nets and collect what’s inside.
We’ve mostly found krill and jellyfish, but occasionally we’ll find a larval fish or squid!
Larval fish and squid found in the pocket nets.
CamTrawl
Near the codend, there is also a camera, referred to as CamTrawl. This camera provides scientists with a visual of what is going into the net, and can be used to help identify species and length of fish that are caught.
CamTrawl (left) and scientists Matthew Phillips and Mike Levine deploying PelagiCam (right).
On this cruise, scientists are also testing a camera that they lower over the side of the ship (without a net), known as PelagiCam. They are hoping that PelagiCam may be able to collect species and length data, supplementing the data captured when processing fish from the trawl. If PelagiCam can record this data accurately, it could provide an efficient complement to trawling, which requires a lot of time and collaboration between different teams of people.
A pollock seen on PelagiCam (left). Posing with scientist Mike Levine in front of the PlagiCam (right).
FS70 Net Sounder
The FS70, nicknamed the Turtle, collects acoustic data and produces a live image of the net’s opening when it is in the water. This data allows scientists and the deck crew to monitor the shape of the net while fishing, ensuring that the net opened correctly. It also monitors when fish enter the net.
FS70 (left), nicknamed the turtle, and the live data it shows scientists during a trawl.
Personal Log:
Going fishing can sometimes be a lot of “hurry up and wait.” After the marine mammal watch, at least one scientist stays on the bridge to monitor the net using the FS70, and the others get ready to process the trawl. Letting the net out and hauling it back in is far from simple, however. It requires constant communication between the bridge and the deck crew, and it can be made more complicated by the weather or equipment malfunctions. Once the net is in the water, trawling can take anywhere from 15 minutes to over an hour.
Opening the codend is always exciting, because we’re never quite sure what we caught. While our target is always pollock, we’ll often find other interesting organisms mixed in as well. Some highlights include rockfish, squid, and a smooth lumpsucker.
Organisms caught in the trawl so far include rockfish, squid, and smooth lumpsuckers.
Did you know?
The net used on NOAA Ship Oscar Dyson was specifically designed for this survey!
Geographic Area of Cruise: Gulf of Alaska (Kodiak – Aleutian Islands)
Date: September 12, 2019
Weather Data from the Bridge
Latitude: 57 35.35 N Longitude: 153 57.71 W Sea wave height: 1 ft Wind Speed: 14 knots Wind Direction: 208 degrees Visibility: 8 nautical miles Air Temperature: 15.4 C Barometric Pressure: 1002.58 mBar Sky: Overcast
Science and Technology Log
Well, we only have a few days left on this trip and it looks like mother nature is going to force us to head for Dutch Harbor a little early. I thought this might be a good time to spend some time sharing some information on some of the species we have been pulling out of the ocean. This is far from a complete list, but just the ones that made “the cut”.
Pollock Age 3
Pollock Age 0
At the top of the list has to be the Pollock. After all, this is the primary objective of this study. On the left is an adult three-year-old pollock and on the right is an age-0 pollock. The sampling of age-0 pollocks is a good indicator of the abundance of the future population.
Coho Salmon
Pink Salmon
There were several species of salmon caught on our trawls. On the left is a Coho Salmon and on the right is a Pink Salmon. These fish are very similar, but are classified as separately Coho Salmon are larger and have larger scales. Coho also has a richer, fuller flavor with darker red meat while the Pink Salmon has a milder flavor and a softer texture.
Another important part of this survey is the collection and measurement of zooplankton as this is a primary food source and the amount and health of the zooplankton will have a lasting impact on the ecology of the fish population in the area.
Capelin is another common fish caught in our trawls. This fish eats krill and other crustaceans and in turn is preyed upon by whales, seals, cod, squid, and seabirds.
The Pacific Saury was a fish that wasn’t expected to be found in our trawls. Also called the knifefish, this species always seemed to be found in substantial quantities when they were collected – as if the trawl net came across a school of them. They are found in the top one meter of the water column.
The Prowfish was another interesting find. This fish is very malleable and slimy. Adults tend to stay close to the ocean floor while young prowfish can be found higher up in the water column where they feed on jellyfish. As with the saury, the prowfish was not kept for future study. It was weighed, recorded, and returned to the water.
Jellyfish were abundant on our hauls. Here are the five most common species that we found.
The Bubble Jellyfish, Aequorea sp., is clear with a rim around it. This jellyfish is fragile and most of them are broken into pieces by the time we get them from the trawl net and onto the sorting table.
The Moon Jellyfish, Aurelia labiata, is translucent and when the sun or moon shines on them, they look like the moon all lit up.
The White Cross Jellyfish, Staurophora mertensi, was another mostly clear jelly that was very fragile. Very few made it to the sorting table in one piece. You have to look close it is so clear, but they can be identified by their clear bell with a distinctive X across the top of the bell.
The Lion’s Mane Jellyfish, Cyanea capillata, are the largest known species of jellyfish. These guys can become giants. They are typically a crimson red but could appear faded to a light brown.
The Sunrise Jellyfish, Chrysaora melanaster, was the most common jelly that we found. It is also arguably the least fragile. Almost all made it to the sorting table intact where they were counted, weighed, recorded, and returned to the water. It lives at depths of up to 100 meters, where it feeds on copepods, larvaceans, small fish, zooplankton, and other jellyfish.
Arrowtooth flounder are a relatively large, brownish colored flatfish with a large mouth. Just one look at its mouth and you can tell how it got its name. Their eyes migrate so that they are both on the right side and lie on the ocean floor on their left side.
Eulachons, sometimes called candlefish, were another common find on the sorting table. Throughout recent history, eulachons have been harvested for their rich oil. Their name, candlefish, was derived from it being so fat during spawning that if caught, dried, and strung on a wick, it can be burned as a candle. They are also an important food source for many ocean and shore predators.
The Vermilion Rockfish – This guy was the only non-larval rockfish that we caught. Most can be found between the Bering Sea and Washington State.
Smooth lumpsucker
Spiny lumpsucker
While the Smooth Lumpsucker is significantly larger than the Spiny Lumpsucker, both have unique faces. The Smooth Lumpsucker is also found in deeper water than the smaller Spiny Lumpsucker.
Squid
Squid
Most of the squid caught and recorded were larval. Here are a couple of the larger ones caught in a trawl.
Seabirds
Black-footed Albatross
There were a
variety of seabirds following us around looking for an easy meal. The Black-footed Albatross on the right was
one of several that joined the group one day.
And of course, I couldn’t leave out the great view we got of Pavlof Volcano! Standing snow capped above the clouds at 8,251 feet above sea level, it is flanked on the right by Pavlof’s Sister. Pavlof last erupted in March of 2016 and remains with a threat of future eruptions considered high. Pavlof’s Sister last erupted in 1786. This picture was taken from 50 miles away.
Personal Log
In keeping with the admiration I have for the scientists and
crew I am working with, I will continue here with my interview with Rob
Suryan.
Robert Suryan is a National Oceanic and Atmospheric Administration Scientist. He is currently a Research Ecologist and Auke Bay Laboratories, Science Coordinator, working on the Gulf Watch Alaska Long-term Ecosystem Monitoring Program.
How long have you been
working with NOAA? What did you do
before joining NOAA?
One and a half years.
Prior to that, I was a professor at Oregon State University
Where do you do most
of your work?
In the Gulf of Alaska
What do you enjoy
about your work?
I really enjoy giving presentations to the general public, where we have to describe why we are conducting studies and results to an audience with a non-science background. It teaches you a lot about messaging! I also like working with writers, reporters, and journalists in conducting press releases for our scientific publications. I also use Twitter for science communication.
Why is your work
important?
Having detailed knowledge about our
surroundings, especially the natural environment and the ocean. Finding
patterns in what sometimes seems like chaos in natural systems. Being able to
provide answers to questions about the marine environment.
How do you help wider
audiences understand and appreciate NOAA science?
I provide information and expertise to make
well informed resource management decisions, I inform the general public about
how our changing climate if affecting marine life, and I train (and hopefully
inspire) future generations of marine scientists
When did you know you
wanted to pursue a career in science an ocean career?
During middle school
What tool do you use
in your work that you could not live without?
Computer! So much of our instrumentation and sampling equipment
are controlled by software interfaces. Also, much of my research involves data
assimilation, analysis, creating graphs, and writing scientific papers.
Although, at the very beginning of my career, most of our data collection was
hand written, as were our scientific papers before typing the final version
with a typewriter. So glad those days are gone!
If you could invent
one tool to make your work easier, what would it be?
For in the office: a computer program that
would scan all of my emails, extract the important info that I need to know and
respond to, and populate my calendar with meetings/events. For the field: a
nano-power source that provided unlimited continuous power for instruments AND
global cell phone or wireless connectivity.
What part of your job
with NOAA did you least expect to be doing?
I joined NOAA later in my career and had
collaborated with NOAA scientists for many years, so everything was what I
expected for the most part.
What classes would you
recommend for a student interested in a career in Marine Science?
Biology, math, chemistry, and physics are good foundation
courses. If you have an opportunity to take a class in marine biology at your
school or during a summer program, that would be ideal. But keep in mind that
almost any field of study can be involved in marine science; including
engineering, economics, computer science, business, geology, microbiology,
genetics, literature, etc.
What’s at the top of
your recommended reading list for a student exploring ocean or science as a
career option?
I originally studied wildlife biology before marine science and one of my favorite books initially was A Sand County Almanac, by Aldo Leopold. For marine biology, I would recommend The Log from the Sea of Cortez, by John Steinbeck.
What do you think you
would be doing if you were not working for NOAA?
I would probably work at a university again –
I was a professor at Oregon State University before working for NOAA.
Do you have any
outside hobbies?
Pretty much any type of outdoor adventure, most frequently kayaking, mountain biking, hiking, camping, and beachcombing with my family and our dogs.
Latitude: 57° 01.32 N Longitude: 155 ° 01.21 W Wind Speed: 14.56 knots Wind Direction: 334° Air Temperature: 15.5°C Sea Temperature: 15°C Barometric Pressure: 1017 mbar
Science and Technology Log
Today marks our sixth day at sea. We are headed north into the Shelikof Strait between the Alaska Peninsula and Kodiak Island. We are continuing along our survey stations with bongo nets and midwater trawls. A bongo net consists of two plankton nets mounted next to each other. These plankton nets are ring nets with a small mesh width and a long funnel shape. Both nets are enclosed by a cod-end that is used for collecting plankton. The bongo net is pulled horizontally through the water column by a research vessel.
Bongo Net Diagram. Image credit: Flanders Marine Institute
Bongo nets on deck
We are using a combination of four total bongo nets simultaneously to sample plankton. Two of our nets are 60 cm in diameter and the other two are 20 cm in diameter respectively. Depending on the depth at each station, the nets are lowered until they reach a depth of ten meters above the sea floor. Scientists and NOAA crew on the scientific deck must constantly communicate with the bridge via radio during this survey to maintain consistent wire angles. Ideally, the goal is to maintain the winch wire angle at 45° so that the water flow into the nets is parallel to the ocean floor.
Me measuring the bongo net wire angle. Photo by Matt Wilson.
Plankton are plants and animals that float along in the oceans’ tides and currents. Their name comes from the Greek meaning “drifter” or “wanderer.” There are two types of plankton: tiny plants called phytoplankton, and weak-swimming animals called zooplankton. Oceanic plankton constitute the largest reservoir of biomass in the world’s oceans. They play a significant role in the transfer of energy within the oceanic ecosystems. Ongoing plankton monitoring data is essential for evaluating ecosystem health and for detecting changes in these ecosystems.
One of the plankton ID cards we use when identifying samples under the microscope
Once the nets are brought back onto the deck, we immediately rinse the nets so that all of the plankton collects in the cod-end (the plastic tube attachment at the bottom). We carefully remove the cod-end tubes and bring them into the wet lab for processing. Using sieve pans, we filter the cod-end sample (plankton) into glass jars. We add formaldehyde and sodium borate to each jar to preserve the plankton for future analysis and study. NOAA Chief Scientist Matt Wilson informed me that all of the sample jars we collect on this expedition will actually be sent to the Plankton Sorting and Identification Center in Szczecin, Poland. Check out their website for more info: https://mir.gdynia.pl/o-instytucie/zaklad-sortowania-i-oznaczania-planktonu/?lang=en .
Plankton sample
Plankton sample
At even numbered stations, NOAA scientists on board will conduct a RZA (rapid zooplankton assessment) of samples collected using a microscope. This rapid assessment of plankton yields current data that allows scientists to quickly evaluate present-day ecosystem health and changes while they await more in-depth sample results and analysis from Poland.
Personal Log
Everything is still going great on day six at sea. Seas are remaining relatively calm, which I am very thankful for. I am actually sleeping more than I do at home. I am averaging about nine to ten hours sleep at night which is amazing! Most mornings, I get up and head down to the gym to run on the treadmill for some much needed exercise. As I said in my second blog, our meals have been delicious. Chief Steward Judy leaves us out some late night treats to help us get through our long shifts. I thoroughly enjoyed some late night ice cream to help me power through the last trawl of the night. I really like lunch and dinner time on the ship because it brings everyone together for a few minutes to catch up and enjoy each other’s company. Most of the scientists and NOAA crew and officers have traveled all over the world on scientific vessels. It is fascinating to hear about all of their stories and adventures. I have already decided to add the ‘PolarTREC’ (Teachers and Researchers Exploring and Collaborating in Antarctica and/or the Artic) Program to my bucket list for a few years down the road. My most favorite organism that we have caught in the trawl so far was this Smooth Lumpsucker.
Smooth lumpsucker
Mr. Lumpsucker
Me and my buddy Mister Lumpsucker – Photos by Lauren Rogers
Did You Know?
The answers to day three blog’s temperature readings were 62.6°F for air temperature and 59°F for sea temperature.
All jellyfish are such weak swimmers that they too are considered plankton. There is also some scientific debate as to whether or not the Ocean Sun Fish (aka Mola mola) is considered a type of plankton. The sun fish is a passive planktonic creature which can only move vertically in the water column since it lacks a back fin. They have a long dorsal and anal fin that help them maneuver clumsily up and down in the water column.
Latitude: 55º 4.07N Longitude: 156º 42 W Wind Speed: 3.2knots Wind Direction: 96º Air Temperature: 10.3º Celsius Barometric Pressure: 1025.7. mb Surface Water temperature: 11.05º Celsius Depth of water column: 1,057.6 meters
If you love science and exploring, consider a career in the NOAA Corps!
NOAA Corps
The NOAA Corps is one of our nation’s seven uniformed services (along with the Army, Marine Corps, Navy, Air Force, Coast Guard, and Public Health Service Commissioned Officer Corps). NOAA Corps officers are an integral part of the National Oceanic and Atmospheric Administration (NOAA), an agency of the U.S. Department of Commerce. NOAA and the NOAA Corps can trace their lineage to 1807 when President Thomas Jefferson signed a bill for the “Survey of the Coast.” The survey work was done by Army and Naval officers along with civilian men and women. The Coast Survey was actually the first federal agency to hire female professionals! Their duties included charting our nation’s waterways and creating topographic maps of our shorelines, which made our marine highways among the best charted in the world.
Today, the NOAA Corps is an elite group of men and women trained in engineering, earth sciences, oceanography, meteorology, and fisheries science. NOAA is comprised of the National Weather Service, National Marine Fisheries Service (NOAA Fisheries), Office of Oceanic and Atmospheric Research (NOAA Research), National Environmental Satellite, Data and Information Service, National Ocean Service, and the Office of Marine and Aviation Operations. NOAA Corps officers operate NOAA’s ships, fly aircraft, manage research projects, conduct diving operations, and serve in staff positions throughout NOAA.
NOAA Officer Spotlight
ENS Lexee Andonian
I had the opportunity to speak with Ensign (ENS) Lexee Andonian (although by the time this is published Ms. Andonian will have been selected for LTJG (Lieutenant junior grade)! ENS Andonian has been a member of NOAA Corps for almost 2 years, and loves her job, but it was not something she originally considered as a career (or even knew about). She first learned about NOAA while working at a rock climbing gym. A patron mentioned it to her, and offered to show her around a NOAA ship. She went home and googled NOAA. With her interest piqued, she decided to accept the patron’s offer, and went to Newport, Oregon to tour the NOAA Ship Bell M. Shimada (which is actually the sister ship of the NOAA Ship Oscar Dyson. A sister ship means they were based off the same blueprint and can serve similar projects.)
ENS Andonian applied for the NOAA Corps, but was waitlisted. NOAA is highly selective and accepts a very limited number of applicants (approximately 15-25 twice a year.) Undeterred, she applied for the next NOAA class, and was once again waitlisted, but this time she was accepted off the waitlist. After 5 months of training at the Coast Guard Academy, she was ready to begin her assignment onboard a NOAA ship, where additional hands-on training occurs non-stop. Each NOAA Corps member wears a multitude of “hats” while onboard. ENS Andonian is currently the Acting Operations Officer, the Navigation Officer, the Environmental Compliance Officer, and the Dive Officer. ENS Andonian loves that her job allows her to see unique places that many people never get to explore since they are not accessible by plane or car. Asked what she misses the most from home, she said, “Bettee Anne” (her dog).
Science and Technology Log
Today I was introduced to a few new species in the fish lab. Until now, most of the jellyfish have been Chrysaora melanasta, which are beautiful and can be quite large, but today I saw 2 egg yolk jellyfish, aptly named as they look like egg yolks.
Egg yolk jellyfish
I also saw a lumpsucker, which is the cutest fish I have ever seen. Lumpsuckers look like little balls of grey goo. He (or she) seemed to look right at me and kept opening and closing its mouth as if trying to say something. Lumpsuckers have a suction cup on their bottom which allows then to adhere to rocks or other surfaces.
Lumpsucker
Personal Log
As a teacher, I create experiences for my students that will take them out of their comfort zone so that they can realize just how much they are truly capable of. On the NOAA Ship Oscar Dyson, it is my turn to step outside my own comfort zone. If you would have told me a few months ago that I would feel comfortable being elbow-deep in live fish and jellyfish, or dissecting fish to see whether they are male or female, or slicing into a fish’s head to collect otoliths (ear bones), I would not have believed you, but that is how I spend every day onboard the Oscar Dyson, and after 2 weeks, it feels like something I have done all my life. It is an experience I highly recommend to everyone!
A slice is made slightly behind the pollock’s eyes.
Otoliths are then removed using forceps.
Walleye pollock otoliths.
Otoliths are bottled and sent for further analysis.
