NOAA Teacher at Sea
Jo Slavitz
Aboard NOAA Ship Oscar Dyson
July 19 – August 10, 2026
Mission: Summer Pollock Acoustic Survey, Leg 3
Geographic Area of Cruise: Bering Sea, Alaska
Date: July 24, 2026
Weather Data from Bering Sea
Latitude: 58° 48.960’ N
Longitude: 173° 43.168′ W
Winds: E at 15-20 mph
Air Temperature: 45.68° F (7.6° C)
“The charm of fishing is that it is the pursuit of what is elusive but attainable, a perpetual series of occasions for hope.” – John Buchan
Science and Technology Log
As the saying goes “there are lots of other fish in the sea,” so how exactly does NOAA Ship Oscar Dyson find mostly Alaskan pollock in such a huge ocean? It’s a combination of structured transect planning, analyzing complex acoustic data and a little bit of luck.
Transects: At first glance the map of the 3 legs of the Alaskan Pollock Survey look like a crazy zig-zag path, so what’s going on and where are we going? The Oscar Dyson is traveling on a transect. A transect is a line drawn by scientists across an area used to measure, count and record the species living there. Oscar Dyson scientists are tasked with figuring out how many pollock are living in the Bering Sea, what age they are and their reproductive stage. As Oscar Dyson travels along each transect, the scientists decide where good places are to sample the pollock population using a long trawl net. It’s difficult to look into the ocean (though we will talk about cameras later) so NOAA scientists actually “listen” for the fish as they swim under the boat.
EchoSound: Many people are familiar with the way animals such as bats and dolphins emit sounds and use echoes to gather information about their surrounding environment. The scientists on the Oscar Dyson also use sound and echoes to gather information about their environment in the Bering Sea. The boat has a sounding board underneath called a transducer that emits energy pulses at different frequencies and receives the echoes as they are bounced back. Objects with different densities send back different amounts of echo energy. Scientists in the Acoustic Lab onboard Oscar Dyson watch a screen for echo patterns that match the patterns that are expected from individuals and schools of pollock.
Check out this image of an echogram. Echograms are a visualization of detected echo sounds. The bright red lines at the top and the bottom of the screen represent the surface and the dense ocean floor. The top wave of blues and greens is referred to as the “munge” ; it is a mixture of stirred up air bubbles, algae, plankton and other things that the team has determined is not pollock. Pollock are primarily in the area just above the bottom to about the middle of the water column. Boney fish such as pollock have a specialized organ called a swim bladder which allows them to take in and release gas, thus changing their density and allowing them to rise and fall in depth like a submarine. Not only is this organ useful to the fish, the air it contains has a different density from the surrounding water and reflects the echo energy that is emitted and picked back up by the ship’s transducer. Look carefully and you can see little colored dots and patches just above the ocean bottom depicted on the echogram. Those are fish and schools of fish. The scientists are confident that they are pollock but to be sure they need to collect a sample of the fish in those areas and get measurements from them.
Trawl: Once a spot has been identified by the scientists, a call goes out to the crew, “Fishing, Fishing, Fishing”. This alerts all aboard that the vessel is going to break from the transect and drop the nets into the spots that had lit up with fish patterns on the echogram. The net is rolled out from a giant spool controlled by the deck crew rather than the scientists. The tip of the net is called the codend, from the old English word “cod” meaning a bag or pouch and this is where the fish are collected. At the opposite end of the net is the opening where fish enter. The weave, or meshes, of the net gets progressively tighter the closer it is to the codend.
Attached to the net are several pieces of equipment that allow the scientist to analyze what is going into the net and when, during the trawl. The FS70, or netsounder, is a bright yellow device that also uses echoes to gather information. This piece is also sometimes called the “turtle.” You can see the crew here connecting it to a special part of the net called the kite. The kite and netsounder are attached and fly just above the opening of the net allowing the scientist to monitor what is going in.
Next to the picture of the crew you can see the image of what is being recorded by the netsounder on an information panel. This image of the “turtle” shows whether it is flying correctly, or oriented in the correct direction. The 2/3 circle image is a visualization of the echos the netsounder is receiving. The rainbow of color on the very bottom of this circle is the echo bouncing back from the bottom of the ocean, above that is another rainbow that represents the bottom of the net, above that if you look closely there are small blue marks just forming an oval with the rainbowed net bottom, those are the top of the net. When fish go into the net, they are represented as small dots, or blobs if a whole school is captured within this oval. The screen showing the echogram from below the ship and the screen with the netscan are placed next to each other on the control panel so that scientists can see the fish coming and hopefully adjust the nets accordingly to catch them.
Scientists only want a sample of the fish, so they monitor the netsounder until they feel they have enough fish to accurately represent what they are seeing and then call “Haul Back.” This call tells the crew to raise the net back onto the boat, and the science crew to put on their wetlab gear in preparation for fish processing.
Try It on Dry Land
Swim bladders allow fish to change the density and buoyancy of their bodies, allowing them to change their position in the water column. Buoyancy is an upward force of an object causing it to float or sink. You can make a simple model of a fish’s swim bladder (and a fun catch game) using items found around your house.
You need:
- Paperclips
- 1 pen cap (Bic pen or other with the stick part)
- 1 soda bottle with cap
- Clay
Instructions:
- Fill bottle to top with water
- Secure clay around stick of pen cap (do not cover opening)
- Bend paperclip to form hook
- Attach paperclip into clay with hook pointing down
- Drop cap/hook into soda bottle so that it floats
- Twist another paperclip into an L shape and drop to bottom
- Put cap tightly on bottle
To Activate:
- Squeeze the bottle and watch the pen cap drop
- Release your grip and pen can will rise
- Practice controlling where in the water column you can direct the cap
- Can you dive the cap to the bottom and hook on to the L shaped paperclip?
What in the Science is going on… The cap holds a bubble of air underneath which allows it to float. When you squeeze the bottle the pressure makes the bubble smaller and changes the density of the cap causing it to sink. A fish’s swim bladder works by the same principles. Find out more here: www.instructables.com/Cartesian-Divers/
Personal Log
Life on Oscar Dyson is different in many ways then life on land. For one, the scientists work in shifts. There is a 4 am to 4 pm shift considered the dayshift and another from 4 pm to 4 am considered the nightshift. Acoustic monitoring and fishing happen all day and all night. I am on the day shift. Adding to the change in daily rhythms is the extended amount of daylight during the Alaskan summer season. The sun is up and bright when I hit my bunk to sleep. The sun will not set until approximately 12:30am, some nights I have gotten up in the night to watch the sunset out my window. I report to the Acoustic Lab at 4 am in the dark to find out what the night shift has been working on, the sun will then rise again at around 7 am. It takes some getting used to as the sun is a natural trigger for my body to know when to be active and when to rest. It makes for a long day, but who can complain with such a stunning beginning.
