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July 27, 2026July 27, 2026

Guy Sturdevant: The Wet Lab, July 18, 2026

NOAA Teacher at Sea

Guy Sturdevant

Aboard NOAA Ship Oscar Dyson

June 21 – July 15, 2026

Mission: Summer Pollock Acoustic Survey, Leg 2

Geographic Area of Cruise: Bering Sea, Alaska

Date: July 14, 2026

Weather Data from the Bridge

N 58.16° W 172.21 °, 0 AMSL

Conditions: Overcast, Seas at < 1’

Visibility: >3 NM

Wind: 4°/ 6 kt

Barometric Pressure 1010.3 mBar

Dry Bulb Temp: 46 ° F

Science Log

Last time we left off with a bin full of fish waiting to be processed. Today we’ll dive into the wet lab where we sort, measure, and process the fish.

a large bin full of hundreds of pollock (fish) — *A full bin of pollock awaiting immediate processing. A full haul can take between 1.5 and 3 hours to process.*

Trigger Warning: In order to provide you with the most accurate understanding of the important science aboard Oscar Dyson, I will describe laboratory procedures and handling processes that require dissection of select fish.

While no one involved enjoys this, it helps scientists understand and protect this natural resource. Fish caught are handled ethically, bycatch (catching species other than the intended target) is extremely minimal, and any sensitive species are immediately released back into the ocean.

The wet lab is just that, wet! Seawater is used to process and clean fish, so every device and surface in the lab must be waterproofed and corrosion-resistant. Before we hop into the lab, we need to don cold-weather rain gear to keep us warm and dry. Once suited up, the science team uses a conveyor belt to sort the haul.

Each haul is unique; the wet lab supervisor decides which sorting method to use. To ensure we have gathered a statistically representative sample of what we are seeing on the echosounder, we aim to process approximately 350 pollock per haul, as well as sample any other species captured. This sample lets scientists divide the acoustic backscatter they recorded on the transect into categories by fish species and size classes- without the catch, there’s no way to know exactly how to assign this backscatter. A skilled acoustic lead scientist aims to land the perfect amount of fish; no more, no less.

view of the sorting table in the wet lab. three people stand - one on each side and one at the end - each wearing orange overalls and large yellow gloves. a pile of pollock (fish) is visible extending down the right side of the sorting table. — A nice, clean haul of juvenile pollock. Night lab lead David Bryan weighs and counts the fish into baskets for further processing. It is important that no bias is introduced in which pollock to include in the sample (no keeping just the big ones, etc.). *Kevin McCarty* *and Julia Clemons are ensuring that only pollock make it to David. Anything else is diverted into other bins and handled separately.*

top down view of a sorting table covered mostly in pollock (fish). yellow gloved hands reach into the frame from both sides of the table and image. one gloved hand lifts a jellyfish out of the pile. — *Day lead Mike Levine removes a Chrysaora jellyfish from the sorting table. Jellyfish are far and away the most common bycatch. Luckily, Chrysaora jellies are unlikely to cause a reaction in humans.*

top-down view of a salmon on an electronic fish measuring board set up on a metal table. a yellow gloved hand places a red magnet at the base of the fish's tail to electronically record its length. — *A rare bycatch, Chum Salmon (Oncorhynchus keta), is* quickly measured, weighed, and returned to the ocean. The icthystick measuring board was developed in the MACE fish lab and is now a commercial product that uses a magnet placed behind the fish’s tail to automatically record its length in CLAMS. A skilled user can process about 400 fish in about 20 minutes. The icthystick is a great example of the innovations being made by the *Midwater Assessment and Conservation Engineering team*.

The Midwater Assessment and Conservation Engineering (MACE) group of the Alaska Fisheries Science Center is responsible for running acoustic pollock surveys representing over 2.5 million square kilometers. To achieve this herculean task, the team has designed and continues to develop novel tools, processes, and methods. This spirit of innovation makes MACE unique.

screenshot displaying output from the computer program used to track fish data inputs; currently, it displays an image of an adult pollock, the name of the scientist doing the measurement, the weight and count — *The CLAMS software suite, developed by MACE, allows them to quickly gather, organize, and analyze large data streams from both the wet lab and the cave.*

In my next (and last!) post, we will look at some of these innovations and how they will empower scientists in MACE and across NOAA to produce the best possible data and science.

Personal Log

As my time at sea draws to a close, I am so grateful for this amazing opportunity and the very special crew of people that make this research happen. In my next and final post, we will look at the career pathways across the different departments and meet some of the new friends I’ve made aboard Oscar Dyson.

four NOAA Corps officers stand in a line at the controls on the bridge of NOAA Ship Oscar Dyson. they each face out the windows, away from the camera. through the bridge windows, we can see green land and other docked vessels. — The junior officers on the bridge during docking at Dutch Harbor. Left to right: LT Jesse Pierce, LTJG Robert Sobelsohn, ENS Miles Litzmann, and ENS Alex Banh. Each operates a single control as ENS Banh practices what might be the toughest parallel parking job in the world.

Emergencies At Sea

During safety drills, we practice mustering to life rafts and donning survival dry suits. As we wait on the back deck, the lead for each lifeboat practices recording key information, such as our current location and the bearing and distance to the nearest land. As I sat on the back deck, flopping like a fish while I squeezed into my survival suit, it struck me that the nearest hospital could well be over 500 kilometers away.

Aboard NOAA vessels, medical emergencies are the responsibility of the medical person in charge (MPIC). MPICs are typically junior officers trained in basic life support who have access to a small medical bay, basic life support equipment, and a limited cabinet of medications. A fair comparison might be to think of the medical bay like the back of an ambulance. Unlike an ambulance, however, the medical bay could be tasked with keeping a person alive for days awaiting evacuation. The MPIC is not alone; they are supported by a team of medical professionals ashore, with access to live feeds of patients’ vitals, who will help guide the MPIC in providing care.

Aboard Oscar Dyson, we were incredibly lucky to have LCDR LeeAnn Keener, a nurse practitioner serving in the US Public Health Service. Were we to have an emergency, LCDR Keener’s training and practice as a licensed medical professional would be a great asset. Currently, only a handful of vessels sail with a licensed medical professional.

orange, white, and navy rescue helicopter in flight over water; the door is open, and one person leans out to help lower another person — *A USCG MH-60 rescue helicopter prepares to lower a rescue swimmer to respond to an emergency. Photo credit: Wikimedia Commons*

Were an emergency to occur, the US Coast Guard would respond from their base in Kodiak, the largest USCG base in the world. First, an MH-60 Jayhawk rescue helicopter would scramble and begin moving towards the vessel in distress; this could take as long as 8 hours to arrive on scene. While underway, the flight surgeon aboard would contact the MPIC and begin preparing to receive the patient or patients. If necessary, Kodiak would begin marshaling additional resources to aid in the evacuation. In some cases, aircraft such as an HC-130 will be dispatched to a remote airfield to serve as the second leg of the emergency relay. Even with this incredible effort, it may take well over a day for a patient to reach the nearest level II trauma center in Anchorage. The total cost of such a remote rescue may well exceed $100,000.

a U.S. Coast Guard rescue plane in flight past large icebergs in an ocean — The USCG operates the HC-130H, sister to the famous AC-130, a highly specialized aircraft designed to respond to nautical emergencies. The C-130 class of aircraft has astonishing range and endurance and can be equipped with specialized electronics, including radar and radio systems, that allow it to serve as a mobile command center at sea. NOAA Hurricane Hunters operate a similar airframe in their mission to predict and study the tropical systems that produce hurricanes. (photo credit: U.S. Coast Guard Visual Information Gallery)

Stay tuned for my final post where we put all the pieces together and profile career opportunities at NOAA!

July 14, 2026July 23, 2026

Guy Sturdevant: The Anatomy of a Trawl, July 13, 2026

NOAA Teacher at Sea

Guy Sturdevant

Aboard Oscar Dyson

June 21 – July 15, 2026

Mission: Summer Pollock Acoustic Survey, Leg 2

Geographic Area of Cruise: Bering Sea, Alaska

Date: July 13, 2026

Weather Data from the Bridge

N 58.16° W 172.21 °, 0 AMSL

Conditions: Overcast, Seas at < 1’

Visibility: >3 NM

Wind: 4°/ 6 kt

Barometric Pressure 1010.3 mBar

Dry Bulb Temp: 46 ° F

Science Log

Now that we have identified likely aggregations of fish using the echosounder, we need to “ground truth.” Out here, that means running a trawl to see what exactly was producing the backscatter noted on the echogram. Doing this at regular intervals allows the science team to be confident in their acoustic observations.

How We Use the Trawl

Let’s walk through the exciting process of a mid-water trawl aboard Oscar Dyson! We pick up the story in the cave. Abigail McCarthy observes an interesting echogram and calls for a trawl.

screenshot of acoustic backscatter readings, represented as a color-coded dots, across several panels. a superimposed text box identifies the depth as 106.7 meters. Each panel represents a different frequency. In this case, there are vertical red marks hovering above the seafloor line visible in every panel. — *This echogram shows interesting backscatter about 10 meters above the seafloor, which is bright across all six frequencies.* Time to go fishing!

“Fishing, Fishing, Fishing!” blares over the radios as all departments are notified, a GPS position is recorded, and acoustic data acquisition is paused.

a blowspout, and a portion of a whale's back - including a small dorsal fin - visible above the ocean. the water is light blue with some whitecaps. the sky is blue-gray, with complete cloud cover. — *Humpback whales frequent the southern end of the survey area. They are here to feast, just like the pollock we are looking for.*

“Marine Mammal Watch ” (15 minutes): our first stop is on the bridge, where at least three pairs of eyes scan the horizon for any sign of cetacean activity. The last thing we want is to catch or harm a whale or porpoise.

[The bridge]: Simultaneously, the NOAA Corps officer on duty navigates the ship to the reported location. They must consider swell, currents, wind, timing, and bottom conditions when lining up for a trawl; when the net hits the water, maneuverability becomes drastically limited.

[The deck]: The Bosun and their team prepare the net and the scientific payload to help monitor the trawl. The scientific payload includes a stereovision camera system, a temperature-depth probe, and a sonar system that will give us a live view of the net mouth as we trawl.

“Splash the net!” (15-30 minutes)

[The deck] The net is dropped into the water, starting with the codend. The deck crew very carefully pays out the net, pausing to mount the science payloads and fly the trawl doors. The trawl doors act as underwater wings that spread the net’s mouth. Fish are funneled from the mouth of the net to the codend, where they will be trapped by a finer mesh.

The codend of the net is lowered into the water and the net plays out.
You can see the door being lowered into the water behind the port tower. Doors help keep the net open.

[The bridge] The lead scientist on duty has relocated to the bridge, where they will coordinate with the OOD to operate the boat and net. The OOD uses the vessel’s speed and the length of the warp wire to control the net’s depth. The lead scientist begins monitoring the mouth of the net using the FS70 sonar that is mounted to the net’s mouth. With this sonar, we can actually see fish as they enter the net.

view of the display of the FS70 echosounder. it shows a radar reading displayed across two thirds of a circle. white arrows have been superimposed on the image to point out the readings representing the seafloor and the net's mouth. — *The FS70 echosounder displays a view of what is happening at the net’s mouth.*

“EQ” (15-90 minutes): The net has reached the target depth, and trawling is truly underway. This phase of trawling feels very much like playing a 1980s wireframe video game. The lead scientist determines when enough fish have entered the net. When they are satisfied, haulback is called.

On the bridge, both the OOD and the lead scientist have access to the EK80 echogram throughout the fishing process.
A view of the mouth of the net. The bright reflector above the net is fish swimming into the net!

“Haulback!” (30-45 minutes): The net (and hopefully the catch!) needs to be brought back onboard.

[The deck] The warps are spooled back in until the trawl doors can be safely stowed; then the net itself is brought aboard. The Bosun and the Survey Tech work together to carefully respool the net to avoid tangles and damage. Several pauses are required to recover the scientific payload. Once the codend is onboard, the haul is dumped into a bin for sorting in the wet lab.

The clump weights are detached from the warp.
The FS70 echosounder is removed from its home on “the kite,” where it has a clear view of the net’s mouth.

[The bridge] The OOD works with the deck crew via hand signals to steer the vessel side to side to aid in spooling the net.

“Crane Dump” (10-15 minutes): To get the fish out of the net, a crane is used to lift the net and fish into “the table”, a hopper that feeds fish into the wet lab.

BSN Alex Steele instructs me in crane operations.
The codend is lifted using the port crane and moved over the sorting table.
Lifting heavy things on a moving boat is inherently a dangerous activity. Deck crewman Steve Rapacki uses a tag line to help control the codend during the crane dump.

Finally, the net is stowed on the spool and readied for its next deployment.

Want to try your hand at trawling? Try out the Midwater Trawling Simulator (now mobile compatible!)

Personal Log

In the last post, we saw Peggy D take to the water for routine maintenance and testing. This week, we get to discuss the other small boat aboard Oscar Dyson. The fast rescue boat (FRB) is designed to respond to emergencies such as a man overboard. This week’s drill was just that, a man overboard drill! Average water temperatures in the survey area hover just above freezing (~5-8 C). In as little as 10 minutes, an unprotected swimmer in these conditions can expect to lose gross muscle control and the ability to aid in their own rescue. Each minute in the water decreases the chance of a successful rescue. Response times matter. Practice matters.

view of the ship's fore deck. a man in a blue uniform tosses an inflatable wearing a life vest over the railing. both hands are extended over his head from the release, and the inflatable flies through the air. — *ENS Alex Banh tosses “Ty” overboard to start the drill. Only a few members of the crew are aware of what the weekly drill will be.*

*Tracking an object overboard is incredibly challenging, even in clear weather.*

CME Christian Benvin demonstrates the appropriate way to track a man overboard, indicating the bearing with his outstretched arm and keeping his eyes focused on “Ty”. A quick glimpse around the ship shows at least half a dozen people demonstrating this simultaneously. To lose track of someone in these conditions may well cost them their life.

The engineering team musters on the starboard aft deck with a throw line. ENG Chelsea is trying to locate “Ty”. She has missed the mark on this run (we all had a good chuckle at this candid moment).

*While Oscar Dyson has come about and approached “Ty” a rescue swimmer has donned a dry suit and their support team has readied the rescue gear.*

*Simultaneously, the crew of the FRB has prepared and launched their vessel. We now have two ways to rescue “Ty”. We will practice both in today’s drill.*

*The FRB takes its turn first. ENG Connor Rauch carefully lines up the vessel with “Ty” while LF John Swenson and ENG Victoria Southwick pull “Ty” into the boat.*

*Now ENS Joshua Bennett gets his chance. He enters the water and immediately swims to the victim.*

*The FRB keeps an eye out in case the assist is needed. Today it will not be; ENS Bennett reaches “Ty” quickly and brings him alongside Oscar Dyson.*

*The victim and rescue swimmer are successfully brought onboard.*

*The FRB is lifted back onto its cradle after a job well done.*

St. Matthew’s Island

Our survey transect brought us close to land at St. Matthew Island. In the Bering Sea, it is easy to pass right by an island and never even see it. On this day, we were treated to breathtaking views of one of the most remote places on Earth.

How to Handle Emergencies on Oscar Dyson

Stay tuned for my next post, where we can look at how medical treatment and emergency evacuation are carried out in these potentially austere conditions.

July 7, 2026July 16, 2026

Guy Sturdevant: The Cave part 2, July 6, 2026

NOAA Teacher at Sea

Guy Sturdevant

Aboard Oscar Dyson

June 21 – July 15, 2026

Mission: Summer Pollock Acoustic Survey, Leg 2

Geographic Area of Cruise: Bering Sea, Alaska

Date: July 6, 2026

Weather Data from the Bridge

N 59.52° W 172.60 °, 0 AMSL

Conditions: Overcast, Seas at < 1’

Visibility: >5 NM

Wind: 90°/ 5 kt

Barometric Pressure 1016.1 mBar

Dry Bulb Temp: 45.3 ° F

Science Log

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.

the EK80 echosounder system, which looks like a stack of black computer housings with cables sticking out of them — *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.

close-up view of a center board - normally mounted beneath the ship, but currently hoisted up in the air attached to some sort of crane. an arrow points out red circles at the base of the centerboard, identifying these as transducers

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.

the previous image of acoustic backscatter readings is repeated here, now with annotation. six vertical panels are identified with different frequencies: 18 kilohertz, 38 kilohertz, 70, 120, 200, 330. along the base of these panels, Guy has added a two arrow ranging from "bigger reflectors" to the left to "smaller reflectors" to the right. An illustration of a cod is at the "bigger reflectors" end of the scale, while krill and copepods appear toward the right side of the range. on the left side of the backscatter panels, there are now a few words along the y-axis, identifying the Surface of the water; the "Munge" (using the mock up album cover) just beneath the surface, Fish question mark in the middle of the water column, and seabed. — 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.

a close up view of three panels (three frequencies) of an acoustic backscatter plot, or echogram. an arrow points to a thin vertical patch of red to identify it as "probable schools of juvenile pollock" — *Younger pollock can gather in schools 20-40 meters tall that appear as very thin red ellipses.*

close-up view of panels of an echogram showing acoustic backscatter readings. an arrow points to blue dots in the 18 kilohertz panel and identifies them as possible dispersed adult pollock. — 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!

example of an echogram (acoustic backscatter plot) with very little shading and few dots. it is labeled "Nobody is home." — *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.

a small boat with a blue hull attached to the deck of NOAA Ship Oscar Dyson, in part by cables extending from davit arms. — *Peggy D secured to the aft hero deck of Oscar Dyson.*

a man and a woman in float coats and hard hats pose for a photo against the railing of the small boat as it churns away from NOAA Ship Oscar Dyson, visible on the horizon — *Peggy D secured to the aft hero deck of Oscar Dyson.*

Guy, wearing a life vest and neon green hard hat, takes a selfie on the small boat. we can see a woman in a float coat and hard hat sitting or crouching in the background, and a third person at the helm in the small boat's cabin. — *LCDR LeeAnn Keener and I enjoying the scenery.*

inside the small boat's cabin, Guy sits at the helm and another crewmember looks on. they both wear life vests and hard hats. — *LCDR LeeAnn Keener and I enjoying the scenery.*

first of three similar images: a person in a float coat and hard hat reaches a pole over the side of the small boat in motion

second of three similar images: a person in a float coat and hard hat reaches a pole over the side of the small boat in motion as a life preserver comes into view

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

a very, very round fish, mouth agape, in a green plastic basket — *This smooth lumpsucker (Aptocyclus ventricosus) is just as surprised to see me as I am to see him.*

underside of the very, very round fish revealing its ventral suction disk — *This smooth lumpsucker (Aptocyclus ventricosus) is just as surprised to see me as I am to see him.*

July 1, 2026July 1, 2026

Guy Sturdevant: The Cave pt. 1, June 29, 2026

Unexpected sea ice south of St Lawrence island on 6/25

NOAA Teacher at Sea

Guy Sturdevant

Aboard Oscar Dyson

June 21 – July 15, 2026

Mission: Summer Pollock Acoustic Survey, Leg 2

Geographic Area of Cruise: Bering Sea, Alaska

Date: June 29, 2026

Weather Data from the Bridge

N 58.6° W 170.4 °, 0 AMSL

Conditions: Fog, Seas at 4’

Visibility: < 3 NM

Wind: 70°/ 9 kt

Barometric Pressure 29.9 inHg

Dry Bulb Temp: 43 ° F

Science Log

So, we’ve taken a chilly dive into the why behind the focus on the pollock. Today, I will take you into “The Cave,” where we can learn how scientists use sound to locate and count pollock. On the port side of the main deck sits a dark, windowless room lit only by the dozen or so monitors adorning its aft wall. A gentle, constant humming fills the room from racks and racks of electronics, servers, and support equipment that dominate the center of this space. While the OOD on the bridge steers this vessel, “The Cave” calls the scientific shots by determining the ship’s course as well as the timing and location of all science operations.

a man and a woman sit in computer chairs at a desk beneath an array of 8 computer monitors; the large computer stack is visible to the right. the two scientists lean far back in their chairs to look up at the screens above. — Abigail McCarthy and Mike Levine discuss plans for the day shift. Time at sea is precious; this vessel operates 24/7 in all conditions. For the past two days, a very quiet, fishless northern extension has limited opportunities. But remember, even a null result is a result!

Acoustics 101

Since the early 20th century, scientists have used the unique ability of sound waves to transmit very efficiently through water for remote sensing. “Pings” of acoustic energy are generated by a transmitter, and then the backscatter (or reflected sound) is detected by a receiver. Early pioneers used sonar to better understand the physical geography of ocean basins in a process called bathymetry.

a graphic showing a cut-out photo of a ship (USS Stewart, DD-13) at the surface of the ocean (depicted as a blue rectangle) above the seafloor (a brown rectangle.) in the animation, upside-down orange parabolas extend from the bottom of the ship toward the seafloor; then right-side up dotted parabolas, like rainbows, extend back from the seafloor up to the ship's bottom. there is a cutout image of the antique echosounder off to the right. There is a speech bubble containing the equation for seafloor depth. The graphic is titled The North Atlantic, 1922: Acoustic Bathymetry — *USS Stewart first tested an early form of echosounder in 1922 as part of preparations for the installation of the Transatlantic cable.*

Not long after the first echosounders made their way aboard ships, scientists realized that as the quality of the instrument increased, they could measure the backscatter (or reflected sound) off of other objects besides the seafloor. Large backscattering layers far above the seafloor were targeted by fishing vessels using the new technology, demonstrating the effectiveness of echosounders at locating marine organisms throughout the water column.

a static graphic showing a cut-out photo of a ship at the surface of the ocean (depicted as a blue rectangle) above the seafloor (a brown rectangle.) 3 upside-down orange parabolas, representing the wave front, extend from the bottom of the ship toward the seafloor; 3 right-side up dotted parabolas, like rainbows, extend back from the seafloor up toward the ship's bottom, representing seafloor backscatter. cutout images of individual pollock fish are pasted in a "school" in the middle of the blue ocean water, and 3 blue rainbow-oriented parabolas extended up from the fish school, representing fish backscatter. this slide is titled: Acoustic Trawling. — *Early innovators in Norway and England reported success in using echosounders to detect large schools of fish and began actively monitoring their behavior (Balls, 1948)*.

The following decades of acoustic research relied on analog, single-beam systems, which were often towed behind or below a vessel and recorded a narrow swath directly below the ship onto a paper echogram.

composite photo of a porcelain wall showing an echogram. arrows and text have been superimposed on the photo to point out the seafloor backscatter and the school of pollock backscatter. in the lower right are the words NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION. — A 3d porcelain rendering of this now-famous echogram (the recorded chart of an echosounder) from the Shelikof Straight adorns the entry to the NOAA Alaska Fisheries Science Center in Seattle. The strong red and yellow reflections that sweep gently across the bottom represent the strong backscatter from the seafloor, and the large red cloud represents a large school of pollock.

The 1990’s welcomed a new era in echosounder technology with the release of the SIMRAD EK-500. This landmark digital echosounder combined multi-frequency operation with improved data processing and integration tools, enabling much better estimates of fish population density and biomass.

a graph of target strength (low, medium, high) v. frequency (kHz, log scale). three lines graph this relationship for fish (swim bladders) at 50-600 mm length; krill at 10-60 mm length; and copepods 0.2-20 mm length. — Larger acoustic targets, such as the swim bladder of a large fish, produce strong backscatter at relatively low frequencies, whereas smaller organisms, such as krill and copepods, reflect sound only at much higher frequencies. Multi-frequency echo sounder measurements allow scientists to discriminate between acoustic targets of different sizes and target strengths and more accurately estimate the biomass of individual organisms as they scroll across the screen.

Next time, we will look at the echograms produced aboard Oscar Dyson and receive a crash course in interpretation from the Cave!

Personal Log

Work hard, play hard is an unofficial motto aboard Oscar Dyson. The officers, crew, and science team are keeping a fierce eye on the World Cup when off duty (Colombia’s goal call-back was a travesty!!).

a 16-competitor bracket drawn on an old hydrographic chart. beneath the chart is the title: The Inaugural Collin McMillan Memorial Biannual Oscar Dyson Amateur Cribbage Tournament. — *The “Inaugural Collin McMillan Memorial Biannual Oscar Dyson Amateur Cribbage Tournament” is underway; stay tuned for updates and potential video coverage of the championship match!*

Guy, wearing overalls and long yellow gloves, holds up a flatfish pointing toward his face, and makes a kissy face at a safe distance. — The future gyotaku model, Northern rock sole (*Lepidopsetta polyxystra*)*, posing for a picture before her big debut.*

fish print, in black ink, of a flatfish — Gyotaku is the traditional Japanese art of collecting fish prints. Engineer Victoria Southwick, ENS Josh Bennett, and Lt. Jesse Pierce captured the print of a Northern rock sole (Lepidopsetta polyxystra) brought up on haul 71, 06/28/26.

Wildlife sightings

highly detailed photo of an albatross floating at the ocean's surface — A Short-tailed albatross (Phoebastria albatrus) follows us during trawling operations, hoping for a fishy treat. This threatened marine bird is a tale of cautious conservation success. Their population in the 1950s dwindled to as low as 25 individuals. Today, roughly 4,200 individuals are known to exist.

Fun Fact

In the Cave, it is not uncommon for the shallow layer to be filled with a mix of non-fish backscatter. Everyone has their pet theories as to what may be the source of these shallow acoustic targets (we know they aren’t fish), but they have all agreed to call it by one name… munge. Below is my artist’s interpretation of Munge as a heavy metal album.

MUNGE album cover

Sources

Balls, R. 1948. Herring fishing with the echometer. Journal du Conseil International pour l’Exploration de la Mer, 15: 193–206.
Korneliussen, R. J. (2018). Acoustic target classification.
Benoit-Bird, K. J., & Lawson, G. L. (2016). Ecological insights from pelagic habitats acquired using active acoustic techniques. Annual review of marine science, 8, 463-490.
Mordy, C. W., Bond, N. A., Cokelet, E. D., Deary, A., Lemagie, E., Proctor, P., … & Wisegarver, E. (2023). Progress of fisheries-oceanography coordinated investigations in the Gulf of Alaska and Aleutian Passes. Oceanography, 36(2/3), 94-100.
De Robertis, A., McKelvey, D. R., & Ressler, P. H. (2010). Development and application of an empirical multifrequency method for backscatter classification. Canadian Journal of Fisheries and Aquatic Sciences, 67(9), 1459-1474.
Simmonds, J., & MacLennan, D. N. (2008). Fisheries acoustics: theory and practice. John Wiley & Sons.
Holliday, D. V., & Pieper, R. E. (1995). Bioacoustical oceanography at high frequencies. ICES Journal of marine Science, 52(3-4), 279-296.
Echoview. (2019). Acoustics Unpacked. https://acousticsunpacked.echoview.com/acoustics/AcousticsUnpacked.asp

June 26, 2026June 29, 2026

Guy Sturdevant: Why Pollock? June 25, 2026

NOAA Teacher at Sea

Guy Sturdevant

NOAA Ship Oscar Dyson

June 21 – July 15, 2026

Mission: Summer Pollock Acoustic Survey, Leg 2

Geographic Area of Cruise: Bering Sea, Alaska

Date: June 25, 2026

Weather Data from the Bridge

N 58.00° W 169.68 °, 0 AMSL

Conditions: Heavy Fog, Seas at 8’

Visibility: < 1 NM

Wind: 130°/23 kt

Barometric Pressure 29.66 inHg

Dry Bulb Temp: 43 ° F

A tufted puffin sails above the Bering Sea. — *A Tufted Puffin sails above the Bering Sea*

Science Log

If you’re anything like me, you’ve never given the pollock (Gadus chalcogrammus) a second thought. However, the humble pollock, which occurs throughout the North Pacific Ocean and is especially common in Alaska, plays a linchpin role in the US seafood industry.

In 2024, pollock accounted for 43% of all seafood caught in the US by weight. That’s bigger than salmon, lobster, and tuna put together!

Clearly, pollock must be providing something of value; why is pollock such a large part of the harvest? Several factors contribute to pollock’s popularity with the fishing fleet.

1. Pollock are relatively easy to catch as they school densely in mid-water. Mid-water trawling can sometimes be much quicker and easier than other types of commercial fishing.

2. Pollock is a lean, lightly-flavored whitefish that can be used as whole cuts or processed into products such as surimi (artificial crab meat) and has been shown to be a good source of lean protein and Omega-3 fatty acids.

A chart comparing the nutritional facts of Alaskan Pollock to beef, chicken, pork, almonds, and plant-based meat alternative. — *A comparison of the nutritional value of pollock to other dietary protein sources.* – *USDA*

3. Pollock has a much smaller lifecycle carbon footprint than other protein sources. Due to the efficiency of mid-water trawling and industry innovations, you can hit your macros while leaving the carbon where it belongs, cycling through the ecosystem.

A comparison of the carbon impact of pollock vs other common animal protein sources.

Pollock sure sounds like a great, sustainable protein source, but let’s take a step back and meet the fish behind the stick!

illustration of a single Alaskan adult pollock against a white background; notably, the pollock has three dorsal fins and two anal fins — An Adult Alaskan pollock (*Gadus chalcogrammus*)

Pollock are a member of the same genus as Atlantic and Pacific cod, and grow to around 20 inches on average over their 15-year lifespan. Their Latin name, chalcogrammus, is derived from the beautiful copper patterns that adorn their dorsal sides.

In winter, pollock move closer to shore, gathering in large schools to spawn. In summer, they migrate farther onto the continental shelf, forming more dispersed schools.

The Midwater Assessment and Conservation Engineering (MACE) Summer Pollock Acoustic Survey helps NOAA track and manage this vital economic and cultural resource by monitoring the location, size, and well-being of the eastern Bering Sea pollock population. This summer, the scientists have extended some of the acoustic transect lines northward to ensure the survey captures a more holistic picture of the population distribution in the eastern Bering Sea.

an animation comparing maps over time of the distribution of pollock abundances in the Eastern Bering Sea — In this animation, lighter colors indicate a higher abundance of pollock at a given location. In 2010, AFSC bottom trawl data showed that the pollock population was concentrated at the far western edge of the study area. Conversely, in 2017, the population was much more evenly dispersed across the region. Observations like these help MACE scientists plan future work to better understand the extent and variability of pollock population distributions across the eastern Bering Sea. data source: FFSC eastern Bering sea bottom trawl survey from https://apps-st.fisheries.noaa.gov/dismap/index.html

Personal Log

As a guest of this crew, it has been great to get to know the science team, the NOAA Corps, and the crew that make Oscar Dyson run like a well-oiled machine. From Frankie in the mess (sooooo good), to the officers on the Bridge, it is evident that everyone WANTS to be here.

Wildlife sightings

🚨Charismatic Megafauna Alert🚨

A humpback whale, just visible at the surface, spouts water off the coast of Dutch Harbor, AK. — *A humpback whale stopped by on our way north from Dutch Harbor, AK.*

Did You Know?

“For the 26th consecutive year, Dutch Harbor, Alaska, led the nation in seafood landed volume (780.1 million pounds, valued at $224.5 million).” (Fisheries of the United States 2023).

From the library

“The war between water and land is never-ending. Waves shatter themselves in spent fury against the rocky bulwarks of the coast; giant tides eat away the sand beaches and alter the entire contour of an island overnight…”

– Corey Ford, Where the Sea Breaks Its Back: The Epic Story of the Early Naturalist Georg Steller and the Russian Exploration of Alaska

Sources

National Oceanic and Atmospheric Administration. (2026, March 10). Fisheries of the Exclusive Economic Zone Off Alaska; Bering Sea and Aleutian Islands; 2026 and 2027 Harvest Specifications for Groundfish. Federal Register, 91(46), 11750-11799. https://www.federalregister.gov/documents/2026/03/10/2026-04684/fisheries-of-the-exclusive-economic-zone-off-alaska-bering-sea-and-aleutian-islands-2026-and-2027

“Frequent Questions: Annual Catch Limit Monitoring | NOAA Fisheries.” Frequent Questions: Annual Catch Limit Monitoring, NOAA, 22 Sept. 2025, www.fisheries.noaa.gov/southeast/sustainable-fisheries/frequent-questions-annual-catch-limit-monitoring.

National Marine Fisheries Service. Fisheries of the United States, 2023. U.S. Department of Commerce, NOAA Current Fishery Statistics No. 2023, Feb. 2026, https://s3.amazonaws.com/media.fisheries.noaa.gov/2026-02/FUS-2023-web.pdf.

Genuine Alaska Pollock Producers. “Sustainability.” Genuine Alaska Pollock Producers, https://www.alaskapollock.org/about-the-fish/sustainability