Tag: NOAA Ship Oscar Dyson

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Nick Lee: Signing Off, July 21, 2024

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 21, 2024

Science and Technology Log:

When I applied to the Teacher at Sea program, I was hoping to use my experience on one of NOAA’s cruises to enhance my AP Environmental Science class. Now, having just completed my time aboard NOAA Ship Oscar Dyson, I’m looking forward to incorporating pollock and fisheries research into my existing curriculum. The scientists’ research involved concepts that are already a key part of the AP Environmental Science curriculum, like biodiversity, sustainable fishing, and ocean currents. I’m excited to engage my students this year with more real life examples and photos from the cruise!

View of mountains from the bridge. The water is calm, and the snow-capped mountains are partially obscured by dramatic gray clouds.
View from the bridge on the last day of the cruise.

I wasn’t expecting to see as many applications of computer science on the cruise – however, I was surprised to learn how much of the scientists’ job on the ship involves coding and statistical analysis. At any given time, it seemed like at least one member of the science team was coding in Python or R, creating new programs and data visualizations that would help make their research more efficient and effective. We relied on many different computer applications to collect both acoustic and trawl data, almost all of which had been coded by the scientists and their colleagues.

MACE MasterApp, developed by scientists to collect and analyze data. This is a screenshot that shows a grid of icons labeled with program names such as "CLAMS QC," "Species Finder," "Transect Events," "Depth Comparison," and "Pies."
MACE MasterApp, the suite of apps the scientists use to collect and analyze data.

Some of these programs didn’t even exist just a few months ago, but they were created when someone on the team recognized an area for improvement. This represents a broader mindset of adaptability and collaboration I noticed among scientists. On the ship, plans constantly changed in response to weather, delays, and equipment malfunctions. While these could be frustrating, the scientists always looked for ways to still complete their research, troubleshooting with each other and with the other ship departments.

The science team on my cruise. Nine people pose for a group photo along a deck railing. Beyond them, we see calm ocean waters, green hillsides, and snow-capped mountains.
The science team on my cruise. From left to right: Mike Levine, Robert Levine, Dave McGowan, Abigail McCarthy, Taina Honkalehto, Moses Lurbur, Sarah Stienessen, Matthew Phillips, Nick Lee (Photo Credit: Emily Resendez).

I also learned how the scientists had been adaptable in their own careers. Most of the scientists I had worked with had not intended to study pollock when they were younger, and some had not even planned on studying marine science. However, when interesting opportunities presented themselves, they took advantage, even when this meant learning about a new type of research or traveling to a new location. Having different academic backgrounds meant the scientists had different perspectives, and each was able to contribute their own ideas on how to improve the group’s research. On this particular cruise, scientists were testing out cameras and studying pollock behavior at night in the hopes of improving their data collection methods for future surveys.

Personal Log:

I just arrived back in Boston after a few long travel days – I took a small boat from the ship to Dutch Harbor, and then I flew to Anchorage, then Seattle, and then finally Boston.

Small boat being lowered from the ship.
Sign warning of eagles. It's a wooden sign resting on the ground in front of a fence, reading "DANGER NESTING EAGLES," with a silhouette of a person with their arms in the air to shield their head from an attacking eagle. Nick does his best to reenact the pose, but there are no live eagles in sight.
From left to right: Small boat being lowered from the ship and an eagle warning sign in Dutch Harbor (Photo Credit: Abigail McCarthy).

I’m still processing my experience as a Teacher at Sea, but overwhelmingly I feel lucky to have spent three weeks aboard NOAA Ship Oscar Dyson and grateful to all of the people I met along the way.

The crew of the ship were all kind and welcoming, and I was able to learn about the other departments on board. I was able to tour the engineering department, and I learned how the ship makes its own freshwater by evaporating seawater. I shadowed the survey technicians as they deployed CTDs (conductivity, temperature, and depth sensor), and I touched water samples they had captured from the bottom of the ocean. During one trawl, I joined the deck crew, and I was able to witness how they safely manage nets containing thousands of pounds of pollock. Finally, I was able to learn about marine navigation from the NOAA Corps Officers, and I was even allowed to (briefly) drive the boat!

Engineering control room.
Nick streaming the net with the deck crew. He wears a heavy reflective coat, gloves, and a hard hat.
Learning to drive the ship. Nick, wearing a blue sweatshirt, stands at the helm and looks ahead. Emily stands nearby, arms crossed, looking in the same direction.
From left to right: Engineering control room, streaming the net with the deck crew (Photo Credit: Mike Levine), and learning to drive from NOAA Corps Officer Emily Resendez (Photo Credit: Savi Morales).

I want to thank all of the crew and officers of NOAA Ship Oscar Dyson for making the past three weeks such a meaningful experience, and I want to thank the science team for letting me contribute to their research and answering all of my questions (special thanks to Robert Levine for editing these blog posts)! Finally, I want to thank Emily Susko and the Teacher at Sea Program for supporting me throughout this entire process.

Did you know?

Applications for next season’s Teacher at Sea Program open in November – more info can be found here!

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Nick Lee: The Night Shift, July 19, 2024

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 19, 2024

Weather Data from the Bridge:

Latitude: 53° 44.5 N

Longitude: 166° 54.0 W

Wind Speed: 15 knots

Air Temperature: 10.9° Celsius (51.62° Fahrenheit)

Science and Technology Log:

As my cruise begins to wrap up, I wanted to highlight some of the people I’ve been working closest with – the scientists on the night shift. Work on the ship continues 24 hours a day, seven days a week, and the night shift works from 4 pm – 4 am. The night shift has the same responsibilities as the day shift of monitoring acoustic data and processing trawls, tasks completed by scientists Sarah Stienessen, Matthew Phillips, and Robert Levine. To learn more about the scientists and their careers, I interviewed each of them:

Why did you decide to become a marine scientist?

Sarah: The short answer is in kindergarten, I checked out a book on dolphins and fell in love with the ocean!

Matthew: I grew up near the ocean, and as a kid, I always loved exploring and finding new fish. I knew I didn’t want to spend every day in an office, and so marine science seemed like a great way to pursue my passion and explore new places.

Robert: I actually wasn’t planning to. I was majoring in geology and environmental science, and I did a field semester in Hawaii. We did a three week class in conservation ecology using passive acoustics, and I thought it was the coolest thing. I did a marine mammal internship with acoustics, and after college, I worked in a zooplankton lab – the rest is history.

Scientist Sarah Stienessen on marine mammal watch. Sarah rests her elbows on a windowsill and looks through binoculars out a large window. Through the windows, we see the sky is gray, and the sea is gray.
Sarah Stienessen on marine mammal watch.

What are your responsibilities during the cruise?

Sarah: My responsibilities are to monitor and analyze the acoustic data and decide when and where to collect a biological sample (trawl) – that’s the daily stuff. I work on combining the acoustic data with the biological sample data to produce abundance and distribution estimates.  I also coordinate pre- and post-cruise logistics.

Matthew: I’m the fish lab lead, so I’m responsible for supervising all of the trawl processing.

Robert: I’m here as an assistant to the fish lab lead and to explore new data types that we could use to enhance our data collection.

Scientist Robert Levine unloading the trawl catch onto the sorting table. Robert wears a heavy orange raincoat and long, elbow-length yellow gloves. He stands behind the sorting table and with his right hand controls the flow of the fish onto the table with a switch or a button on the wall.
Robert Levine unloading the trawl catch onto the sorting table.

What do you enjoy the most about your work?

Sarah: On the boat, it’s teamwork and camaraderie with colleagues. On land, it’s the strategizing and planning around the logistics of fieldwork, both small scale and large scale.

Matthew: Seeing a species that’s new to me! I love seeing new fish, birds, and marine mammals.

Robert: I enjoy the balance between office work, getting to do fieldwork, and working on instrumentation. This group does a lot of research, but it’s all applied, which is the best part.

What part of your career did you least expect?

Sarah: Acoustics, fish, and Alaska!

Matthew: I never expected to be spending so much time in Alaska.

Robert: I never would have thought I would be on a boat actually doing the fishing.

Scientist Matthew Phillips troubleshooting PelagiCam. We see Matthew through an open window in a metal wall, perhaps an outer wall of the ship. He wears a heavy orange reflective coat and a black beanie and works at a laptop on a table at the window. A cable extends from inside the lab through the window out of frame.
Matthew Phillips troubleshooting PelagiCam

What advice do you have for a young person interested in a career in marine science?

Sarah: Take lab-based course work that’s marine related and hands-on. Also, volunteer, intern, try to get a glimpse of the real life experience of what marine science is like. It’s good for giving you connections and for seeing if it’s something you really want to do.

Matthew: Be open-minded about different opportunities and unthought-of locations!

Robert: Find the thing that you like to do or are really good at. If you like chemistry or computer science, get a degree in that. Then apply it to marine science – you don’t have to have a biology degree and you can actually be more effective with an outside perspective.

Personal Log:

When I first boarded NOAA Ship Oscar Dyson I was hoping to be assigned the day shift (4 am – 4 pm). However, after I adjusted to the different sleep schedule, I found myself enjoying the nighttime hours when the ship was quieter. There is still a lot of fish processing to do during the night shift  – this cruise, the ship has actually processed more trawls during our shift! 

While nights are often busy in the fish lab, we’ll also have some downtime between trawls. During a few of these breaks, we played cribbage, a card game that scientist Robert Levine taught me early in the cruise. We’ll also frequent the galley for midnight meals together and to finish off the last of the dessert that our awesome stewards – Danielle and Missy – prepared that day (some highlights include butter mochi, lemon meringue pie, and a zucchini chocolate cake)!

cribbage board and stacks of playing cards on a table
Cribbage Game

On a couple nights, we’ve tracked our candy consumption, competing with the day shift to see who eats more. Being a science team, we felt compelled to convert between different units, expressing our final answer in terms of portion of the bag, mass, and individual sour patch kids!

Did you know?

Because pollock behavior changes at night, the scientists on this particular cruise don’t trawl between sunset and sunrise.

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Nick Lee: The Data, July 15, 2024

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 15, 2024

Weather Data from the Bridge:

Latitude: 59° 51.9 N

Longitude: 173° 53.5 W

Wind Speed: 11 knots

Air Temperature: 6.1° Celsius (42.9° Fahrenheit)

Science and Technology Log:

On my cruise, scientists take acoustic measurements along the length of each transect. To ensure that they are accurately estimating the abundance of pollock, they take steps to separate out any backscatter that they believe didn’t come from pollock.

Scientists then apply algorithms to the data in order to estimate pollock abundance over the entire survey area. First, they break up the transect into 0.5 nautical mile (NM) sections and record the average backscatter for that section. Specifically, scientists are interested in the areal density – the amount of backscatter per square nautical mile (NM2).

This data can be challenging to interpret, so one way the scientists represent it visually is with a stick plot over the survey area:

Stick plot showing acoustic backscatter from the 2022 pollock survey. This is a simple map of the Bering Sea, where the land of Alaska appears in gray and the water is white with some bathymetric lines. The transect lines run straight, at a slight angle on this rotated map, across the waters. Yellow bars of different sizes stick up off the transect lines at an angle.
Acoustic backscatter from the 2022 pollock survey.

In this graphic, the transect lines are shown in black, and the density of acoustic backscatter for each 0.5 NM section is represented with a yellow stick. The longer the stick, the greater the density of backscatter at that location.

Scientists then use this data to perform calculations on the entire survey area, including the space in between transects. For each 0.5 NM section of transect, the acoustic density is extrapolated halfway to the next transect on either side.

Diagram showing transect lines, and how acoustic density is applied across the survey area. Three gray vertical lines, evenly spaced, are each labeled "transect line;" dotted lines mark the distance halfway between each transect line. A smaller portion of the middle transect line is colored red instead of gray. It's labeled with a parallel double-sided arrow marking out "0.5 nautical mile." A red box the height of that red section stretches as far to the left and right as the next dotted halfway line; one side is labeled "half distance to next transect."
In this diagram, the red line represents a 0.5 NM section of transect for which acoustic density is calculated. This acoustic density is then applied to the entire pink rectangle, which extends halfway to the next to the transect on either side.

By doing this process for every 0.5 NM section of transect studied, scientists are able to calculate values of acoustic density for the entire survey area.

Map of current survey area with transect lines and boxes showing the area over which transect data is extrapolated.
Map of current survey area and transect lines (black), with boxes (purple) indicating the area over which data from each transect is extrapolated.

Getting from acoustic density to pollock abundance takes another set of calculations, this time making use of trawl data. The pollock caught in each trawl can vary drastically in terms of size – some trawls are mostly juveniles, some trawls are mostly adults, and some are an even mix of both. For a given location, scientists use data from the nearest geographic trawl to estimate the distribution of fish in that area.

Distribution of pollock centered around 20-30 cm. This is a bar chart. The x-axis displays length in centimeters (0 to 80 cm) and the y-axis displays proportion of the catch (0 to 0.125). The majority of the bars are black, but a minor portion are colored partially red, indicating proportions of identified male pollock, or blue, indicating proportions of identified of female pollock.
In some trawls, the most fish were within 20-30 cm in length (above) while in others, most fish were over 40 cm in length (below).
Distribution of pollock centered around 40-50 cm. This is a bar chart. The x-axis displays length in centimeters (0 to 80 cm) and the y-axis displays proportion of the catch (0 to 0.125). The majority of the bars are black, but a minor portion are colored partially red, indicating proportions of identified male pollock, or blue, indicating proportions of identified of female pollock.

Having trawl data is necessary to convert the acoustic data into fish abundance because small and large pollock do not reflect backscatter equally. Scientists have studied this, and they have created a relationship for the different backscatter reflected by different length pollock. Using the distribution of pollock in the nearest trawl, scientists are able to proportionally allocate the observed backscatter to pollock of different lengths.

Graph showing that as pollock length increases, acoustic backscatter also increases. The x-axis shows pollock length in centimeters (0 to 80) and the y-axis shows acoustic size in "(TS, dB re 1 m2)", ranging from -50 to -30. A blue line curves gently from the lower right corner ("small fish, weak backscatter") to the upper right corner ("large fish, strong backscatter.")
As pollock length increases, backscatter also increases. 
(Equation from Lauffenburger et al., 2023. Mining previous acoustic surveys to improve walleye pollock (Gadus chalcogrammus) target strength estimates, ICES Journal of Marine Science, Volume 80, Issue 6, August 2023, Pages 1683–1696, https://doi.org/10.1093/icesjms/fsad094)

As an example, let’s simplify the two locations sampled in the graphs above. Suppose the first location had only 20 cm pollock, the second had only 40 cm pollock, and equal backscatter was observed at both sites. Scientists know that, all else being equal, 20 cm pollock produce less backscatter than 40 cm pollock. This means that in order to reflect the same backscatter, there must be a greater number of 20 cm pollock than 40 cm pollock.

By repeating a similar process for each geographic location, scientists are able to estimate the number of pollock in the entire survey area!

Personal Log

The sailing and many of the operations of NOAA Ship Oscar Dyson are done by NOAA Corps officers. I hadn’t heard of the NOAA Corps before sailing, but I’ve since learned that they play an important role in facilitating NOAA research.

To learn more about the experience of NOAA Corps officers, I interviewed Ensign Savi Morales.

Ensign Savi Morales working with John Swenson, a member of the deck crew. Engisn Morales wears the blue every day uniform of the NOAA Corps and stands at a bank of navigational computers on the bridge. Both men gaze down at a display screen.
Ensign Savi Morales (left) on the bridge collaborating with John Swenson, a member of the deck crew.

Why did you decide to become a NOAA Corps officer?

I’ve always wanted to support the protection of the environment and mitigating climate change. After college, I was trying to figure out where I would contribute the most. I really loved being out on the water, and I had sailed plenty but I wanted to find a way to combine my interests in an environment I contribute the most. The NOAA Corps felt like it was a combination of those things.

I also loved the idea of working with the crew, engineering department, and science. I really enjoy that mixture of groups we have aboard Dyson, which makes every trip’s dynamic different. There’s also a lot of hands-on experience on the bridge deck making our 12 days packed with projects I work on. The NOAA Corps embraces a diverse skill set in order to think and act like a Swiss army knife and be a jack of all trades.

What are your responsibilities on board the ship?

My responsibilities are two 4-hour bridge watches as a Junior Officer of the Deck as I work towards becoming a fully qualified Officer of the Deck. In between my watches I work on tasks related to my responsibilities as the Dyson’s damage control officer, assistant navigation officer, and assistant public affairs officer. I track the sea service hours for our augmenting and personal crew, which they can use to upgrade their license. I maintain flags, and I do monthly safety rounds, inspecting fire extinguishers and fire stations. 

What do you enjoy the most about your work?

I enjoy meeting the characters that come to the Dyson, definitely an eclectic but fun group. I also enjoy how much they’ve thrown me into the mix and had me figure things out. It’s a little bit of a trial by fire, but I learn really quick and I’d rather learn by doing.

What part of your job with NOAA did you least expect to be doing?

Checking fire extinguishers, there’s about 100 on board and they all need to be checked monthly. It takes about 3-4 hours.

Here in the Bering Sea you hear about the big, massive waves, but it’s not always like that. The Aleutian Islands are gorgeous with lots of wildlife. I don’t think I’ve seen this many bald eagles, orcas, or puffins in my entire life. They always brighten my day.

What advice do you have for a young person interested in a career in the NOAA Corps?

NOAA Corps requires you to have a four-year college degree in order to apply. Other than that, I’d say find opportunities to go out on the water. There’s high school scholarships, there’s college scholarships. You can also volunteer if you have time. I volunteered at the UC Davis Bodega marine lab. I visited once a week just to hang out with the scientists, with the crew to see if this is what I liked. Be curious and experience things for yourself!

Did you know?

NOAA Corps is one of the country’s eight uniformed services, and its officers operate NOAA ships and aircraft around the country. After completing basic training at the US Coast Guard Academy, NOAA officers assist in fisheries research, seafloor mapping, monitoring atmospheric conditions, and may respond to natural disasters and extreme weather. Learn more at the NOAA Corps website here!

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Nick Lee: In the Fish Lab, July 12, 2024

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 12, 2024

Weather Data from the Bridge:

Latitude: 60° 02.17 N

Longitude: 176° 37.3 W

Wind Speed: 14 knots

Air Temperature: 5.5° Celsius (41.9° Fahrenheit)

Science and Technology Log

Once the trawl is completed, the codend is unloaded onto a conveyor belt for sorting. Usually, we just sort by species, picking out any organisms that aren’t pollock and storing them in separate baskets. Overall, I’ve been surprised with how “clean” or uniform the catches have been. We will usually have some jellyfish, but other than that we tend to have only a few fish of other species in a catch with hundreds or thousands of pollock.

Pollock on the conveyor belt. We can see the orange rain coats and long yellow gloves of two scientists standing nearby.
The catch is first emptied onto a conveyor belt where it is sorted by species.

When the catch has a mix of juvenile and adult pollock, we’ll also sort them by size, which roughly correlates to age group. The size cutoff used for sorting is only an approximation of age (the exact age is determined later), but it is still useful in ensuring that we sample a consistent number of each size class in every trawl.

Distinguishing between the larger juveniles and smaller adults on the belt can be tricky, so on one trawl we got creative and found what we named a “measuring fish.” This fish was the smallest length that had been designated as an adult in the previous trawls – anything smaller we left on the belt with the juveniles and anything larger we put in a separate basket with the adults. While not the most conventional solution, it served our purpose well and showed that anything can be made into a measuring instrument!

Nick is wearing a heavy orange rain coat and long yellow gloves. He holds up two pollock fish vertically, comparing their lengths to one another. We see more fish on a sorting table in the background.
Using a “measuring” fish to sort the catch according to size (Photo Credit: Matthew Phillips).

Once the fish are sorted, we take length and weight measurements for a representative sample of all species in the trawl. We measure the length of hundreds of pollock in a given trawl, so luckily the system is very efficient. 

When I length a pollock, I’ll grab the fish in one hand and place it on the magnetic length board so that its head is against the end at zero. Then I’ll use my other hand to straighten the fish and place a magnet at the fork of the tail. The length board records where the magnet touches the length board, measuring what is known as the “fork length” of the fish.

Pollock on length board; its head faces toward the left side of the board, near a digital meter reading the length. toward the right side, a red magnet is placed at the fork of the fish's tail.
The length board records where the red magnet is placed.

For a subsample of pollock, we will also record the sex and maturity of each individual. To collect this data, we’ll first make a cut along the side of the pollock. This allows us to observe the pollock’s ovaries or testes and compare them to a chart showing the stages of development. Based on the time of year, most of the pollock we catch are in the “developing” stage. Also visible are the pollock’s liver and its stomach, which is often filled with krill!

Three people stand at a long metal table wearing heavy orange raincoats and gloves. White bins, a white cutting board, and a measuring board line the table. Matthew, in the foreground, holds a fish up with two hands over a measuring board, and looks at someone over his right shoulder. Nick, in the middle, looks down at the fish that Matthew holds, and a third scientist stands beyond Nick, looking on as well.
Scientist Matthew Phillips showing me how to identify the sex and maturity of a pollock (Photo Credit: Mike Levine).

For a subsample of the pollock in this group, we’ll also collect otoliths, which are similar to tree rings in that they allow scientists to visually determine the age of the individual. Otoliths are part of pollock’s inner ear, and they help the fish to detect vibrations in the water. Like tree rings, they grow throughout a fish’s life, adding visible layers each year. During times when the fish is actively feeding (usually during the summer), an opaque layer forms around the otolith. In contrast, when the fish is eating less, the otolith layer formed is translucent. By studying otoliths, scientists can determine the age of a fish, as one opaque layer and one translucent layer together represent one year. (Source: https://www.fisheries.noaa.gov/national/science-data/age-and-growth)

Teacher at Sea Nick Lee removing an otolith. Nick wears a heavy orange raincoat and long yellow gloves. He holds part of a pollock in his right hand and with his left hand holds up a small white object (the otolith) with tweezers.
Extracting an otolith from the head of a pollock (Photo Credit: Mike Levine).

One important and sometimes overlooked step in scientific data collection is the clean-up. At Codman Academy, we use the phrase “Leave No Trace,” and I try to model this idea in the fish lab as well. Working with fish can be smelly, and the smell only grows when fish are allowed to sit for extended periods of time. The process of recording sex and extracting otoliths can be especially messy, so we are constantly spraying down baskets and surfaces (and each other!) between data collection steps.

All of the fish that are processed are ultimately disposed of overboard – usually during the processing of the trawl dozens of seabirds follow the ship in search of discarded fish!

View through a doorway of an outer deck; over the railing we see seabirds flying past the fish lab. The sky and the water are gray.
Seabirds flying past the fish lab.

Personal Log

Outside of my stateroom, there is a tongue-in-cheek poster claiming to be a “Bering Sea Weather Guide.” The poster has the labels “Good Day,” “Some Days,” and “Other Days,” below paint swatches, all of them different shades of gray. There are also gray paint swatches for “Summer,” “Winter,” and “Days Ending in Y.”

"Bering Sea Weather Guide," a collection of gray paint swatches labeled: Most Days, Good Days, Some Days, Other Days, Last Week, Next Week, This Week, Days Ending in Y, Summer, Fall, Winter, Spring
“Bering Sea Weather Guide” outside my stateroom.

We’ve certainly had our share of gray days this cruise, and I’ve become used to falling asleep to the sound of the ship’s foghorn. However, we’ve also gotten a few moments of sunshine and blue sky, providing some great moments for bird and whale watching from the bridge. Being on the night shift, I’ve also been able to observe a couple of sunsets from the water!

View from the bridge on a clear day - blue skys, scattered fluffy white clouds
Sunset behind NOAA Ship Oscar Dyson - nice mix of purples, pinks, blues, yellows
View from the bridge on a clear day (left) and sunset at sea (right).

Did you know?

Because we are so far north and west in the time zone, the sun sets very late here, usually around 1 am!

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Nick Lee: Finding Fish, July 6, 2024

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 6, 2024

Weather Data from the Bridge:

Latitude: 61° 15.0 N

Longitude: 174° 56.8 W

Wind Speed: 13 knots

Air Temperature: 5.3° Celsius (41.5° F)

Science and Technology Log:

On NOAA Ship Oscar Dyson, the science party’s mission is to understand the population of walleye pollock in the Eastern Bering Sea. To collect data, scientists rely on two main tools: acoustics and targeted trawling. Before any trawling can happen, scientists must first locate fish using acoustics, so I’ll be focusing on acoustics in this blog post – stay tuned for a post on trawling next time!

Scientists use two kinds of acoustics: active and passive. Many of my students are familiar with how bats use echolocation to navigate in the dark – active acoustics relies on the same principle. First, the echosounder on the ship emits a pulse of sound, or ping. This sound travels through the water and bounces off of objects that have different densities than water (such as fish, krill, or the ocean floor). The echosounder then “listens” for and records these echoes, also known as backscatter. Passive acoustics work similarly, except the echo sounder only listens for sound and doesn’t emit any itself.

illustration of a pulse of sound, depicted as a triangle, emanating from the bottom of a ship at the surface of the ocean. the triangle encompasses some of the sea creatures swimming by (depicted as simple white silhouettes) and ends at the ocean bottom.
The echosounder emits a pulse of sound, which gets reflected by objects of different densities, like pollock. Image Credit: Wieczorek, Schadeberg, Reid (2021) “How do Scientists Use Sound to Count Fish in The Deep Sea?” Frontiers for Young Minds. https://kids.frontiersin.org/articles/10.3389/frym.2021.598169

The greater the distance between the echo sounder and the object reflecting the pulse, the greater the amount of time between when the signal was emitted and backscatter. Based on this time, echosounder can determine the depth of the object producing the backscatter. This information is represented visually in an echogram:

Screenshot of an echogram. Backscatter is depicted as colored dots on a grid. in this case, the dots are densest and darkest at the shallowest depths (the ship bottom) and the deepest depths (the hard ocean botttom)
Screenshot of an echogram. The space between vertical grid lines represents 100 pings, and the space between horizontal grid lines represents 10 meters of depth.

The echogram shows depth on the y-axis and time on the x-axis. The intensity of backscatter is color-coded, where more intense backscatter is represented with red and brown, and less intense backscatter is represented with blue and green. The vertical grid lines represent all the backscatter from one ping, and the space between lines represent 100 pings.

On the cruise, pings are typically emitted at a rate of 1 Hz, or once every second. With every new ping, the echo sounder adds data to the right end of the echogram. This means that the horizontal grid lines represent the backscatter at one depth over time (or distance, if the ship is traveling at a constant speed).

At least one scientist monitors the backscatter throughout the duration of the transect. During the first day, the echogram was blank except for some lower-intensity backscatter near the surface and high-intensity reflection from the ocean floor. Because the mission of this cruise is to survey pollock, which tend to live at greater depths, we don’t pay much attention to the backscatter near the surface which is comprised of smaller organisms like krill. However, when scientists notice backscatter consistent with scattering from pollock, they may trawl to collect a sample for more detailed biological information.

Screenshot of two echograms showing low-intensity backscatter and high-intensity backscatter.
Echograms from two different locations showing low-intensity backscatter (left) and high-intensity backscatter (right). When the backscatter looks as it does on the right, the science team may decide to fish in that area.

As we traveled along the first transect line, there was very little backscatter that the science team thought represented pollock. Our CTD (conductivity, temperature, depth) measurements also showed that the water temperature was cold, right around freezing. This may suggest that we were traveling through the Bering Sea cold pool, a mass of cold water that forms from melting ice. This water tends to be too cold for pollock and other fishes, however, other animals, such as snow crabs, can still survive the lower temperatures. Fish like cod prey on snow crab, so the cold pool offers these crab an important refuge from predators. Read more about the importance of the cold pool for crab here!

GIF showing historical bottom temperatures in the Bering Sea from 1983 to 2018. The years 2015, 2016, and 2018 are notably warm.
Historical bottom temperature showing cold pool in blue / purple (Image Credit: NOAA Fisheries)

Personal Log:

The start of the cruise has been busy learning new faces, maritime practices, and scientific terms. However, in the past few days, with the help of meclizine (seasickness medication), I’ve begun to feel more settled and like I have some sense of routine.

When I’m on shift, I bounce around between a few different places. The science team tends to be in the acoustics lab, where we monitor backscatter and make decisions on when to fish.

Photo of the acoustics lab. Computers and many computer screens mounted on the wall above a long desk.
Acoustics lab, also called “the cave” for its lack of windows.

Once the scientists decide to fish, we first go up to the bridge, where NOAA officers control the direction and speed of the ship. The bridge has windows on all sides, so we’re able to make sure there are no marine mammals before putting the net in the water.

From the bridge, you can also see the trawl deck, where the deck crew works in collaboration with NOAA officers to put the net in the water. Once the fish are caught and hauled back to the ship, the science team processes the catch in the fish lab.

Photo of the bridge. Navigation computers surrounded by windows.
Photo of the trawl deck. Unspooled trawl net visible in A-frame.
The bridge and its view of the trawl deck.

When we’re not working, we’ll grab food from the galley / mess deck. The stewards on the ship serve three meals a day, but since I’m on the night shift, I often heat up leftovers or take advantage of the wide selection of snacks they leave out. There’s also a lounge, two gyms, and places to do laundry while at sea!

Photo of the galley, the ship's cafeteria. Tables and chairs, a refrigerator. Chair legs are capped with tennis balls to reduce sliding.
The galley, where food is available 24 hours a day!

Did you know?

NOAA Ship Oscar Dyson  has six onboard laboratories including a wet lab, dry lab, electronics lab, bio lab, acoustics lab, and hydrographics lab. Read more about the ship here!