NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
June 22 – July 15, 2019
Mission: Pollock Acoustic-Trawl Survey
Geographic Area of Cruise: Kodiak Island, Alaska
Date: June 26, 2019
Weather Data from the Bridge:
Latitude: 58º 33.15 N
Longitude: 152º 58.87 W
Wind Speed: 17.5 knots
Wind Direction: 229º
Air Temperature: 13º Celsius
Barometric Pressure: 1020.2 mb
Today we did our first two trawls of the trip. According to Webster’s dictionary, trawl is defined as the act of fishing with a trawl net, which is a large conical net dragged along the sea bottom in order to gather fish or other marine life. It can also mean the act of sifting through something as part of a search. Both definitions are accurate for what is done on the NOAA Ship Oscar Dyson.
The Oscar Dyson uses a variety of nets to catch the fish being studied. One net that has been used for many years is called an Aleutian Wing Trawl (or an AWT). The mesh size of the AWT is ½ inch. Attached to the AWT net are smaller nets (called pocket nets) which also have a ½ inch mesh size. The new net being used this year is an LFS 1421, which has a 1/8 inch mesh size. It has 9 pocket nets, also with 1/8 inch mesh size. It is thought that fewer fish will escape the LFS net because the mesh size is smaller, in turn allowing the scientists to get a more accurate picture of the fish and other creatures living in the areas they are trawling. Trawls are being conducted using both nets (back-to-back) to determine the extent to which the new net is more efficient and provides a more accurate measure.
Once the nets are pulled in, the processing begins. The main net (i.e., codend) is emptied onto the large processing table in the fish lab.
Each pocket net is emptied into a separate plastic bin. The fish are then identified, weighed, measured, and sometimes dissected in order for us to accurately determine the age and sex of each fish.
Otoliths (ear bones) and ovaries are collected from a sample of the walleye pollock caught in the codend of the net. Otoliths allow scientists to determine the age of the fish. Over time, ridges form on the otoliths, and are indicative of age in much the same way a tree’s age can be determined by counting the rings of its trunk.
Ovaries are collected to be sent back to the lab as part of a long-term histology study which hopes to determine whether walleye pollock experience multi-batch spawning events (i.e., do pollock spawn more than one time) within or between seasons. Histology, also known as microscopic anatomy or microanatomy, uses a microscope to study the anatomy of biological tissues. In contrast, gross anatomy looks at structures without a microscope.
After a trawl, scientists onboard the NOAA Ship Oscar Dyson examine the ovaries with the naked eye to determine the reproductive stage of the walleye pollock that has been caught. There are 5 stages: Immature (not yet capable of spawning, typically age 0-2); Developing (beginning to develop the ability to spawn) Pre-spawning, Spawning, and Spent (completed spawning). Once a pollock spawns, it begins the cycle again beginning at step 3 (pre-spawning). Additionally, the histology study also hopes to determine whether the spawning stages being designated by scientists during the cruise are in fact accurate.
Elementary Math Fun
Let’s say 200 total fish were caught in the new LFS 1421 net, including the nine pocket nets attached.
Pocket nets 1, 2 and 3 each had 20 age-0 pollock in them.
Pocket nets 4, 5 and 6 each had 13 lantern fish in them.
Pocket net 7 had 3 small herrings in it.
Pocket nets 8 and 9 each had 2 age-1 pollock in them.
How many fish were in the codend or main part of the net?
As a Southern Californian, I imagined Alaska to be cold even in the summer, and packed sweaters and a big puffy winter coat. Apparently shorts and t-shirts would have been more appropriate! The weather in Kodiak has been warm and beautiful, with the sun shining until midnight.
My first day in Kodiak was a free day, so I joined the science team on a hike up Barometer Mountain, which many say is the most difficult hike in Kodiak. It is 2100 feet straight up a very steep, rocky, brush-filled path, and then 2100 feet down that same, steep path. It was quite the challenge, but the view from the top was magnificent.
At present, there are 31 people onboard the NOAA Ship Oscar Dyson, including NOAA corps officers, engineers, deck personnel, cooks, scientists, interns, and me, the NOAA Teacher at Sea. The ship, which was originally launched in 2003, and commissioned into service as a NOAA ship in 2005, is named for Alaskan fisherman and fishing industry leader Oscar E. Dyson. It is one of the most advanced fisheries research vessels in the world, due in part to its acoustic quieting technology. This allows scientists to monitor fish populations without concern that the ship’s noise will affect the behavior of the fish.