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:
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.
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.
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.
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.
(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.
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!