Richard Chewning, June 13, 2010


NOAA Teacher at Sea
Richard Chewning
Onboard NOAA Ship Oscar Dyson
June 4 – 24, 2010

NOAA Ship Oscar Dyson
Mission: Pollock Survey
Geographical area of cruise: Gulf of Alaska (Kodiak) to eastern Bering Sea (Dutch Harbor)
Date: June 13, 2010

Weather Data from the Bridge

Position: Eastern Bering Sea
Time: 1530
Latitude: N 56 15.380
Longitude: W 164 14.010
Cloud Cover: Overcast with light spray
Wind: 30 knots
Temperature: 5.4 C
Barometric Pressure: 1002.7 mbar

Science and Technology Log

Around 0940 Thursday morning we began our first summer 2010 pollock survey transect. Researchers have been conducting acoustic pollock trawl surveys since 1979 and bottom trawl surveys since the1950’s. The 31 transects in this year’s survey run roughly north south and progress from the eastern Bering Sea across to Russian waters in the western Bering Sea. The transect lines range in length from 60 to 270 nautical miles and are spaced 20 nautical miles apart. A nautical mile is slightly longer than a standard mile and is useful for navigating charts (maps used at sea). Only surveying during daylight hours, the Dyson will continue to run these transects till the beginning of August. A transect is a path (usually a straight line) during which the number of occurrences of an observable fact are counted (such as the abundance of pollock).

The beginning transect was marked by the launching of an expendable bathythermograph (XBT) probe. While the name might seem long and somewhat complicated sounding at first, the instrument and data being recorded are actually quite straightforward. Expendable refers to the fact that the probe is not recovered after being deployed. How is the data sent back to the Dyson you ask? Two long thin copper wires uncoil from the launcher and probe allowing data transfer back to the Dyson. The wires are broken by hand once the probe has reached the bottom. The rest of the story is revealed by subdividing the word ‘bathythermograph’ and defining its parts. ‘Bathy’ is a prefix that means deep or at depth. ‘Thermo’ is another prefix that refers to heat or temperature. Finally the word ‘graph’ means to draw a relationship between multiple variables (such as depth of the water and temperature). So an expendable bathythermograph is a disposable probe that profiles the temperature from the surface to the sea floor.

XBT probe and launcher

The XBT is a very helpful tool that enables the scientists onboard the Dyson to gather temperature data while on the move. Being able to capture this data without slowing down and stopping is a big time saver. Bringing a ship to a stop on the water takes much more time than stopping a car on the highway, and deploying a reusable instrument to the bottom and back takes even more time, manpower, and resources. Temperature data allows fish biologists to better understand how water temperature and the abundance of pollock and their food supply are related.

Darin deploying XBT

Later that afternoon, we also performed our first Tucker trawl. The Tucker trawl is a cleverly designed system of three nets that allows for three discrete (separate) samples during a single deployment. The Tucker trawl is designed to catch the zooplankton (animal-like plankton) that pollock eat such as euphausiids. This net allows researchers to study the differences of zooplankton distribution at various layers in the water.

Deploying the Tucker trawl

Tucker trawl messenger

To catch these small organisms, the net needs to a have very small openings. In fact, the openings in the net are only half a millimeter in width or roughly 1/3 the thickness of a dime! The three nets are attached to a metal frame mounted on metal skis that resembles a backwards dog sled. These skis allow the sled to slide along the seafloor and avoid snagging any obstructions. The Tucker trawl is initially deployed with one net open. The first net is closed and the next net is opened using a heavy brass messenger sent down the wire connecting the Tucker trawl to the Dyson. The messenger is attached to the wire cable at the surface and allowed to slide down the cable to the net being towed in the water. The impact of the messenger triggers a spring in a latch that closes one net and opens another net. The second net is closed and the third net is opened in the same fashion. Samples are taken at the surface, at the bottom, and evenly from the seafloor all the way to the surface. Attached to the sled are sensors to record temperature and depth, the flow of water passing through the net, and the time the net spends on the bottom. The catch is collected at the end of the net in a removable cod end jar. Any jellyfish are removed from the catch, identified, and measured. The remaining zooplankton is weighed, and a small subsample is saved and preserved for later identification.

Richard sending messenger down to the Tucker trawl

Euphausiid

Hyperiid amphipod

Personal Log

At sea, a person can easily lose track of time and even forget the day of the week as work aboard the Oscar Dyson continues uninterrupted seven days a week. I was reminded that today was Saturday by a special meal served by the galley. Rick and Floyd prepared a delicious dinner of real Alaskan king crab, prime rib, baked potatoes, vegetables, and fresh baked bread. This was a real treat (along with the cookies and cream ice cream, always a fan favorite) for the crew. There was plenty to go around, and all were well satisfied.

This was actually not my first encounter with king crab on this cruise. The day before, we had the unprecedented surprise of catching a red king crab with the Tucker trawl during the bottom net deployment. To the best of the knowledge of all the scientists onboard, this had never happened before. You might remember that the Tucker trawl is designed to catch zooplankton, which are typically small in size. This unlucky crab was so large she didn’t even fit in the cod end collection jar at the end of the net. In the end the crab was lucky as we opted to release her after recording her weight and species as we already had enough crab in the freezer for dinner the following night!

Richard holding red king crab

Dinner! Lucky for her, the crab Richard’s holding was released back to the sea!

Leisure Activities

Time spent not working onboard the Dyson can be considered among a person’s most precious possessions. Working long hours, the NOAA Corps officers, visiting scientists, and crew aboard the Dyson usually only have a few hours of time before starting their next scheduled watch or shift. Sleeping is often the first order of business on a person’s to do list. Whether you take only a short nap or can sleep for several blissful hours, time in one’s rack (bed) is essential for a productive, happy, and safe crew. Often one’s sleep schedule will necessitate missing a meal but the rest gained seems well worth the trade off. A very nice service offered by the galley is making and setting aside a plate for those crew members missing a meal if requested.

Other down time activities include reading, listening to music, and working out. The Dyson also has an impressive movie collection (including many recent titles not yet released on DVD) that is administered by the Department of the Navy. New titles are added monthly. The Dyson has a very comfortable lounge for watching movies that also includes a wide selection of magazines and books. Keeping connected with the outside world is also very important while at sea. With relative reliability, people can access the internet to answer emails, pay bills online, and surf the web for news and can call friends and family back home using the satellite phone.

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