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)
Dates: June 6-7, 2010
Weather Data from the Bridge
Position: Snakehead Bank, Gulf of Alaska
Time: 1700 hrs
Latitude: N 56 00.390
Longitude: W 153 46.380
Cloud Cover: Overcast
Wind: 12 knots from the SE
Temperature: 7.1C
Barometric Pressure: 1016.9 mbar
Science and Technology Log
I have been impressed by the wide array of oceanographic research the Oscar Dyson is able to conduct. A few examples include biological studies of organisms ranging from microscopic plankton to massive marine mammals, collecting a variety of weather data, describing both physical and chemical characteristics of seawater (such as temperature, salinity, chlorophyll, and dissolved oxygen), conducting acoustic surveys of marine life and the sea floor, and much more.
One of the Dyson’s ‘bread and butter’ surveys is our survey studying the distribution, biomass, and biological composition (male/female ratios and age) of walleye pollock in the Bering Sea. Walleye pollock is a very important fishery for Alaska. You have almost certainly been a part of this fishery as most fish sandwiches in fast food restaurants and fish sticks in the frozen food section of your local grocery store are Alaskan-caught pollock.
One of the Oscar Dyson’s many tools for this research is her impressive array of acoustic sensors located on the ship’s hull and centerboard. The centerboard is an extension of the hull that can be raised and lowered in the water in order to position most of the Dyson’s sensitive acoustic sensors below the bubbles often found near the water’s surface. These air bubbles interfere with sound traveling through the water and degrade the quality of the data being collected. The Dyson has six downward looking centerboard-mounted transducers, each transmitting a different frequency. Why so many frequencies? Since different types of marine organisms interact with sound waves differently producing varying acoustic signatures, the Dyson must be equipped with a variety of sensors to best characterize the variety of marine life encountered during a survey.
For example, lower frequencies are better suited for fish such as pollock and the higher frequencies are better suited for smaller organisms such as plankton. Think of transducers as a downward shining flashlight illuminating the depths of the ocean with sound rather than light.
The Dyson also has other acoustic sensors such as the ME-70 multibeam echosounder that has the unique ability to look over a much wider angle through the water. Acoustic research works on the same echo location principle that bats and marine mammals employ to find food and navigate. By sending out sound waves and measuring the time the sound takes to travel back after encountering an object, one can learn a great deal about that object’s properties such as distance, size, and movement.
Before traveling to the Bering Sea to start our pollock survey, the Dyson’s scientists must take great care to ensure that their echo-sounding equipment is calibrated correctly. Calibrating the transducers is similar in concept to tuning a piano string or zeroing a sight on a rifle. To this end, the Dyson anchored in Three Saints Bay, a sheltered bay protected from the wind, waves, and currents of the open ocean, at least theoretically. While a troublesome storm passed almost directly overhead, scientists from the Midwater Assessment and Conservation Engineering (MACE) Program (part of the Alaska Fisheries Science Center (AFSC) located in Seattle, WA), the US Fish and Wildlife Service (FWS located in Anchorage, AK), and the Pacific Institute of Fisheries and Oceanography (located in Vladivostok, Russia) worked diligently to fine tune their acoustic sensors.
Paul Walline, Patrick Ressler, Darin Jones, Bill Floering, and Mikhail ‘Misha’ Stepanenko worked day and night calibrating their equipment using metal spheres positioned directly under the ship.
Spheres of different sizes and materials with known acoustic signatures (such as tungsten carbide and copper) are used to calibrate the transducers.
The crew of the Dyson works around the clock as ship time is precious. The scientists work 12 hour shifts, either from 4am to 4pm (the shift to which I am assigned) or from 4pm to 4am. The acoustics lab where the data is collected and analyzed is affectionately called ‘The Cave’ as there are no portholes (windows) to tell the time of day outside.
Personal Log
I wasn’t sure when the Dyson arrived at Three Saints Bay as I had retreated to my stateroom early in the evening of the 4th as I was feeling the effects of the rolling seas. I am being berthed with the ship’s 2nd Cook, Floyd Pounds, who is also from Georgia but now calls the Dyson home.
Floyd works with the Chief Steward, Rick Hargis, who has been with NOAA for 20 years and is originally from Washington State. So far the meals have been very filling and satisfying (there is even an ice cream bar!).
My stateroom is located on the crew deck, one level below the main deck near the bow (the pointy end of the ship) on the starboard side (the right side when facing the bow). Utilizing every nook and cranny and with no wasted space, my berth is quite cozy and is surprisingly comfortable. Fortunately with the help of some seasickness medication, I soon found my sea legs and awoke feeling refreshed and hungry (always a good sign!). Seasickness comes from conflicting messages received from the inner ear and the eyes by the brain (the inner ear feels the motion of the boat rolling and pitching in the water but the eyes report a stable environment confusing the brain).
A person soon observes that safety is paramount onboard the Dyson as with any NOAA vessel. For example, within 24 hours of leaving Kodiak, the entire crew conducted fire and abandon ship drills. These drills are conducted once a week and are essential for maintaining readiness in the event of an emergency. During the abandon ship drill, I was able to practice donning my survival suit just like our visiting Coast Guard kids did in Kodiak! Although the suit is designed to be quite snug to keep cold water out and to keep the body warm, I was thankful I didn’t have to put the suit to the test by going over the side. To my surprise, Chief Marine Engineer Jerome ‘Jerry’ Sheehan and ENS Russell Pate did just that, going for a dip in the frigid 7.3 degrees Celcius or ~45 degrees Fahrenheit waters! Jerry and Russell used dry suits to scuba dive under the Dyson to check the hull, the prop, and the transducers for anything out of place such as barnacles on the transducers or tangled fishing gear. The only discovery was of a piece of bull kelp snagged on one of the blades of the prop which may explain a noise that was heard on the hydrophones (microphones located under the Dyson’s hull) during our departure from Kodiak.
After completing our calibrations and safety operations, the Dyson sailed for a site called Snakehead Bank located 60 nautical miles southeast of Kodiak. The name comes from the bathometric profile of the seafloor of this area which resembles the head of a snake. We soon began conducting camera operations for ground-truthing sea floor composition that I will discuss in my next log!
Where did the NOAA ship Oscar Dyson’s name originate?
The Oscar Dyson is named for an Alaskan fisherman who was very influential in fisheries development and management in Alaska. From his days as a commercial fisherman, Oscar Dyson was a pioneer and advocate for Alaska fisherman and was very influential in the growth of this important industry. Alaska’s commercial fishing industry spans the state and includes salmon, herring, pollock, various shellfish, and various ground fish like halibut. While traveling through the Ted Stevens International Airport in Anchorage, I learned that Alaska is a land defined by water with more than three million lakes and more coastline than the rest of the United Sates combined! Alaska is also the only state in the US to have coastlines with three different oceans/seas: the Pacific Ocean, the Arctic Ocean, and the Bering Sea.
