NOAA Teacher at Sea
Joan Shea-Rogers
Aboard NOAA Ship Oscar Dyson
July 1-22, 2018
Mission: Walleye Pollock Acoustic Trawl Survey
Geographic Area of Cruise: Eastern Bering Sea
Date: July 8, 2018
Weather Data from the Bridge
Latitude: 53º N
Longitude: 166ºW
Sea Wave Height: 1.5 feet
Wind Speed: 25 Knots
Wind Direction: SW
Visibility: 15 miles
Air Temperature: 52ºF
Water Temperature: 46º F
Barometric Pressure: 1010.61mb
Sky: Overcast
Science and Technology Log
What kinds of fish live in the Bering Sea? How many pollock are in the Bering Sea? Where are the pollock in the Bering Sea? How big are the pollock in the Bering Sea?
Those are just a few of the questions that the fisheries biologists on NOAA Ship Oscar Dyson work to answer during each voyage. In my last blog, I talked about the need to manage the pollock fishery in order to protect this important ocean resource because it provides food for people all over the world. It is important, then, to be able to answer the above questions, in order to make sure that this food source is available each year.
How do they do it? There are two main sources of information used in the Acoustics-Trawl (or Echo Integration Trawl) survey to determine the abundance and distribution of pollock in a targeted area of the Bering Sea. One is acoustics data, and the other is biological-trawl data.
Acoustics:
Acoustic data is continuously collected along a series of parallel transects with a Simrad EK60 scientific echo integration system incorporating five centerboard-mounted transducers (18-, 38-, 70-, 120-, and 200- kHz). In other words: There are 5 sound wave producers (transducers) attached to the bottom of the ship, each one emitting sound waves at different frequencies. This allows scientists to look at different organisms in the water column. Different types of organisms reflect different amounts of energy at different frequencies. The amount of acoustic energy reflected by an individual animal is called the target strength, and is related to the size and anatomy of the species. For example, a fish with a swimbladder (like pollock) reflects more energy than a fish without a swimbladder because its properties are very different from the surrounding water. Some ocean dwelling organisms don’t have swim bladders. Flatfish stay on the bottom so they don’t need the buoyancy. Floating organisms like jellyfish don’t have them. These organisms will look differently than pollock on an echogram because they have a smaller target strength.
Transducers convert mechanical waves (sound waves) into an electrical signal and vice versa (like both a loudspeaker and a microphone combined). They contain piezoelectric materials sensitive to electricity and pressure: if a voltage is applied to them, they make a pressure or sound wave (transmit), and when a sound wave passes over them, it produces a voltage (receive). When a sound wave (echo from a fish) is received, electoral signal is sent to a computer, which displays the signals as pixels of varying colors as the ship moves along (depth changes up and down on the left of the image, and time and location changes along the bottom of the image). This datum is used to estimate the number and type of fish in the water column, and to determine where the ship should fish next.
The size and colors on the images (called echograms) represent the backscatter at different depths and is related to the density of fish and their target strength. But, since they are dots on a screen, specific identification is not possible. The scientists assume certain strong signals are pollock based on the information they have but, those dots could be other fish. To determine what kind of fish are in the water column at this location, how many are there, and how big they are, other data must be obtained. Biological Trawl Data provides that additional information. More about that in my next blog post……I bet you can’t wait!
Personal Log
The Calm Before the Storm:
So far my trip has been smooth sailing, literally. As NOAA Ship Oscar Dyson sails across the Bering Sea there is a bit of rocking the ship experiences at all times. This is easy enough for one to get used to and sometimes it even becomes comforting, like being rocked to sleep as a child. You adjust to the motion. Over the past couple of days I have been hearing talk of a storm coming our way. On a ship, there are many preparations that occur in order to get ready for a storm. Many items are always secured, such as shelves that have a wall in front so that things don’t fall off. There are “handle bars” in showers and next to toilets (think about that). Along hallways and stairways there are handrails on each side. Mini refrigerators in staterooms are bolted to walls. In fact most things are bolted to walls or stored in containers that are bolted to the wall. In the mess hall (dining room) condiments on tables are in a box so they can’t slide off.
Why do you think this coffee mug is shaped like this (wider at the bottom than the top)?
Ans. The wider bottom of the mug above prevents it from sliding as the ship rocks.
Our bulletin board reminds us to secure for bad weather. This morning, I put small items in drawers, stowed books on shelves and packed my equipment (phone, laptop, camera, chargers and small items in a backpack that can be safely secured in my locker (the “closet” in my stateroom).
In talking to my shipmates with at sea experience, I am getting lots of helpful hints about storm preparations and strategies to use during the storm. Here are some of those suggestions:
*always hold on to railings with both hands when walking or going up steps. At all other times, remember to keep one hand for you (to do whatever you are doing) and one hand for the ship (to hold on).
*keep something in your stomach at all times, even if you are not feeling well
*eat saltines
*drink lots of water
*when sleeping in your bunk, place pillows between you and the edge so as not to roll off (I will definitely follow this one, as I am on the top bunk) It also depends upon which direction the ship is rolling. Pillows may need to be put between your head and the wall to prevent head bumps
*go to the lower parts of the ship because the top part will sway more with the waves
I also have been wearing patches to prevent seasickness. Hopefully they will continue to help. Only time will tell how we weather the storm (pun intended). Let’s hope it moves through quickly.
Those pictures certainly spark the memory banks. Those green hills in Dutch Harbor look the same as they did in 1984 or so. LOL, a girl behind every tree.
So True! I had forgotten that saying but that is also still true…..The only thing that looked the same in Dutch, was the Russian church in Unalaska…and the green treeless hills….
So very interesting. I shall read on to see if the storm occurs.