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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.

  • view from an upper deck over the aft deck, as the teal trawl net pays out through a large yellow A-frame.
    The codend of the net is lowered into the water and the net plays out.
  • view from an upper deck over the aft deck, focused on the A-frame, though which we see the "doors" of the trawl suspended before entering the water after the net.
    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.

  • view of the echogram generated by the EK80. we can see a depth reading of 99.94 meters.
    On the bridge, both the OOD and the lead scientist have access to the EK80 echogram throughout the fishing process.
  • view of the display of the FS70 echosounder. it shows a radar reading displayed across two thirds of a circle. a white arrow has been superimposed on the image to point out the readings representing fish entering the net's mouth.
    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.

  • view from an upper deck of two crewmembers on the aft deck, near the A frame.
    The clump weights are detached from the warp.
  • view from an upper deck over the aft deck. crewmembers on the aft deck kneel or bend to work as a trawl net extends from a spool into the water, over their heads.
    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.

  • view from an upper deck over the aft deck. a crane is visible to the right of the A-frame.
    BSN Alex Steele instructs me in crane operations.
  • view from an upper deck over the aft deck. the crane works to lift the filled trawl net out of the water.
    The codend is lifted using the port crane and moved over the sorting table.
  • view from the side - a crewmember steadies the heavy net with a line as the crane lifts it over a 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.

One Reply to “”

  1. Wonderfully descriptive narration, felt like I was there with y’all to help ‘rescue Ty’!
    Thanks! 🖖🥰👍

    Reply

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