NOAA Teacher at Sea
Johanna Mendillo
Aboard NOAA Ship Oscar Dyson
July 23 – August 10, 2012
Mission: Pollock Survey
Geographical area of the cruise: Bering Sea
Date: Wednesday, August 1, 2012
Location Data from the Bridge:
Latitude: 62○ 18’ N
Longitude: 178○ 51’ W
Ship speed: 2.5 knots (2.9 mph)
Weather Data from the Bridge:
Air temperature: 9.5○C (49.1ºF)
Surface water temperature: 8.5○C (47.3ºF)
Wind speed: 9.1 knots (10.5 mph)
Wind direction: 270○T
Barometric pressure: 1001 millibar (0.99 atm)
Science and Technology Log:
In the last few days, we have crossed into the Russian Exclusive Economic Zone, sampled, and are now back on the U.S. side! Unfortunately, students, there was no way for my passport to get stamped. There was no formal ceremony, and we will cross back and forth many times in the next two weeks as we do our science transects, collecting Pollock, but the science team took a moment to celebrate— and I snapped a quick picture of the computer screen.
I would now like to introduce you to one of the most simple and valuable tools we use on board to measure a sample of Pollock- the Ichthystick.
First, some background. Each day we “go fishing” 2-4 times with our mid-water and bottom trawls. “Trawling” simply means dragging a large net through the water to collect fish (and you will learn more about the different types of nets we use quite soon). After the trawl, we bring the net back on board and see what we have caught!
There are many types of data we collect from each catch- first and foremost, the total weight of the catch and the numbers and masses of any species we catch in addition to pollock. So far, we have collected salmon, herring, cod, lumpsuckers, rock sole, arrowtooth flounder, Greenland turbot, and jellyfish on my shifts! Our focus, though, of course, is pollock. For pollock-specific data, we keep a sub-sample of the catch, usually 300-500 fish, for further analysis, and we release the rest back into the ocean.
From this sub-sample, I help the scientists collect gender and length data. As I mentioned in my last post, we also collect otoliths from the sub-samples so that the age structure of the population can be studied back in Seattle. The most straightforward and obvious data, though, is simply measuring the length of the fish, which takes us back to the wonderful contraption known as the Ichthystick!
Now, scientists cannot determines the age of a pollock simply from measuring its length- there are many factors that determine how fast a fish can grow, such as access to food, space, its overall health, environmental conditions, etc. But, by collecting length data and combining it with age data from otoliths, scientists can begin to see the length ranges at each age class and the overall “big picture” for the population emerges.
And again, once the age structure and population size of pollock in the Bering Sea are determined for a certain year, management decisions can be made, commercial fish quotas are set for the upcoming fishing season, and there will still be a suitable population of fish left in the ocean to reproduce and keep the stocks at sustainable levels for upcoming years.
So, it clearly does not make much sense to measure pollock with a ruler, paper, and pencil. To measure hundreds of fish at a time, the NOAA team has developed a simple yet ingenious measuring tool, powered by magnets, and transmitted electronically back to their computers for easy analysis- the Ichthystick!
The Ichthystick may simply look like a large ruler, but it consists of a sensor and electronic processing board mounted in a protective (& waterproof!) container. Inside, the sensor processes, formats and transmits the measurement values of each fish to an external computer that collects and stores the data.
Interestingly, the board works with magnets and makes use of the property of magnetostriction.
With magnetostriction, magnetic materials change shape when exposed to a magnetic field. Magnetostrictive sensors can use this property to measure distances by calculating the “time of flight” for a sonic pulse generated in a magnetic filament when a measurement magnet is placed close to the sensor. Here, in the picture, I am placing the fish along the sensor and holding the measurement magnet in my right hand.
To determine the distance to the measurement magnet, the elapsed time between when I touch the magnet to the board to generate the ultrasonic pulse and when the pulse is detected by the sensor is recorded– and that time is converted to a distance (using the speed of sound in that material), which is equal to the fish’s length!
Now, the “measurement magnet” is referred to as the “stylus”, and it is a little white plastic piece, the size of a magic marker cap, which contains the magnet embedded into the bottom. You simply strap the stylus onto your index finger with velcro (so that the north pole of the magnet is facing down toward the sensor) and are ready to begin measuring! The magnet inside is a small neodymium magnet, chosen because it has a very strong magnetic field. Each time a measurement is recorded, a chime sounds, and I know I can go on to measuring my next fish! At this point, I have measured a few thousand fish!
Personal Log:
Let’s continue our tour aboard the Oscar Dyson! I think it is fair to say that scientific research makes one hungry! I have enjoyed meeting Tim and Adam, the stewards (chefs) onboard the Dyson, devouring their delicious meals, and spending time talking with the officers and crew in the galley (kitchen) and mess (dining hall). As you can see from my picture, the first thing you notice are the tennis balls on the bottoms of the chairs! Why do you think they are there?
As in most things related to ship design, planning for rough seas is paramount! So, in addition to tennis balls, which stop the chairs from sliding around, there are bungee cords that attach the chairs to the floor. The dishes are also strapped down and most items are in boxes, bins, or behind closed doors. But do not let that fool you— there is a LOT of food in there! I have enjoyed many a midnight snack- fruit, yogurt, ice cream bars, cereal bars, cookies, and soup to name just a few. In addition, there is a salad bar and a selection of leftover dinner items available to reheat each night. Since I am on the 4pm-4am shift, I have been missing breakfast, and I have been told I must have at least one hot cooked-to-order meal before I depart!
I was a little surprised to see a mini-Starbucks on board too! It is quite a setup, complete with pictures and directions on how to make each concoction:
Dennis, one of the Survey Technicians who works on the overnight shift with me, promised to make me a hazelnut latte if I could correctly predict the number of pollock in a trawl, Price-Is-Right style. I finally won a few nights ago….
Interestingly, there are no mechanisms in place to help the stewards cook in rough seas, but Adam assured me that he has never had a dinner for thirty slide off the grill and onto the floor! Adam has been working in the NOAA fleet for over 10 yrs., including 7 yrs on the Miller Freeman, the precursor to the Oscar Dyson. He has been onboard the Dyson for almost a year. Tim has just joined the Dyson on this cruise and was previously in our home state— aboard the Delaware out of Woods Hole, Massachusetts! Before joining NOAA, he worked on several supply ships that sailed across the world. Each has been quite friendly and helpful as I learn to navigate my way around both the ship and my new schedule. One of our frequent conversations is menu planning and the all-important-dessert on the schedule for each night. So far, I have enjoyed apple cobbler, pineapple upside down cake, snickers cake, carrot cake, brownie sundaes, oatmeal raisin cookies, and… Boston cream pie!
One last Q: How many dozens of eggs do you think Tim and Adam will go through on our 19-day cruise with 30 people on board? Write your guess in the comment section and I will announce the answer in my next post…
