NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
July 23 – August 11, 2012
Mission: Alaskan Pollock Survey
Geographical Area: Bering Sea
Date: July 28, 2012
Ship speed: 3.8 knots (4.4 mph) currently fishing
Weather Data from the Bridge
Wind Speed: 6.9 knots (7.9 mph)
Wind Direction: 30°T
Wave Height: 2ft with 2-4ft swells
Surface Water Temperature: 8.7°C ( 47.7°F)
Air Temperature: 7.9°C ( 46.2°F)
Barometric pressure: 1005.8 millibar (0.99 atm)
Science and Technology Log:
Since the main goal of this voyage is the acoustic-trawl survey of the mid-water portion of the Alaskan pollock population, I thought I would start by telling you how we go fishing to catch pollock! This isn’t the type of fishing I’m used to… Alaskan pollock is a semi-demersal species, which means it inhabits from the middle of the water column (mid-water) downward to the seafloor. This mid-water survey is typically carried out once every two years. Another NOAA Fisheries survey, the bottom trawl survey, surveys the bottom-dwelling or demersal portion of the pollock population every year. I will begin by describing how we are fishing for pollock on this acoustic-trawl survey.
The Oscar Dyson carries two different types of trawling nets for capturing fish as part of the mid-water survey, the AWT (Aleutian Wing Trawl which is a mid-water trawl net) and the 83-112 (a bottom-trawl net that is named for the length of its 83 foot long head rope that is at the top of the mouth of the net and the 112 foot long weighted foot rope at the bottom of the mouth of the net). One of the research projects on board the Oscar Dyson is a feasibility study that involves a comparison of the AWT and using the 83-112 bottom-trawl net as if it were a mid-water net. The 83-112 is much smaller than the AWT, so there is concern with the fish avoiding this net and thus causing a reduction in catch. While the bottom trawl survey acquires good information on the bottom-dwelling pollock using the 83-112 bottom trawl, if they also used this net to sample in mid-water they could help “fill in” estimates of mid-water dwelling pollock in years when the acoustic mid-water trawl survey does not occur.
When the net is deployed from the ship, the first part of the net in the water is called the cod end. This is where the caught fish end up. The mesh size of the net gets smaller and smaller until the mesh size at the cod end is only ½ inch (The mesh size at the mouth of the net is over 3 meters!).
The AWT is also outfitted with a Cam-Trawl, which is the next major part that hits the water. This is a pair of cameras that help scientists identify and measure the fish that are caught in the net. Eventually, this technology might be used to allow scientists to gather data on fish biomass without having to actually collect any fish (more on this technology later). This piece of equipment has to be “sewn” into the side of the net each time the crew is instructed to deploy the AWT. The crew uses a special type of knot called a “zipper” knot, which allows them to untie the entire length of knots with one pull on the end much like yarn from a sweater comes unraveled.
Along the head rope, there is a piece of net called the “kite” where a series of sensors are attached to help the scientists gather data about the depth of the net, the shape of the net underwater, how large the net opening is, determine if the net is tangled, how far the net is off the bottom, and see an acoustic signal if fish are actually going into the net (more on these sensors later, although the major acoustic sensor is affectionately called the “turtle”).
Once the kite is deployed, a pair of tom weights (each weighing 250 lbs), are attached to the bridal cables to help separate the head rope from the foot rope and ensure the mouth of the net will open. Then, after a good length of cable is let out, the crew transfers the net from the net reel to the two tuna towers and attach the doors. The doors act as hydrofoils and create drag to ensure the net mouth opens wide. Our AWT net usually has a 25 meter opening from head rope to foot rope and a 35 meter opening from side to side.
The scientists use acoustic data to determine at what depth they should fish, then the OOD (Officer on Deck) uses a scope table to determine how much cable to let out in order to reach our target depth. Adjustments to the depth of the head rope can be made by adjusting speed and/or adjusting the length of cable released.
The scientists use more acoustic data sent from the “turtle” to determine when enough fish are caught to have a scientifically viable sample size, then the entire net is hauled in. Once on board, the crew uses a crane to lift the cod end over to the lift-table. The lift-table then dumps the catch into the fish lab where the fish get sorted on a conveyor belt. More on acoustics and what happens in the fish lab in my next blog!
WOW! What an adventure!!! So I must get you caught up on some of the happenings thus far. After a mix-up where my reservation was cancelled on the Saturday afternoon flight from Anchorage to Dutch Harbor and the threat of being stranded in Anchorage for another day, I finally made it to Dutch. The weather cooperated (which is not the case more often than not), and we landed on Dutch Harbor after a quick refueling stop in King Salmon. Since we landed after 8pm, we went straight to one of the few restaurants in Dutch Harbor and had a late dinner before heading to the Oscar Dyson for the night.
Sunday morning, we went with several of the scientists out to Alaska Ship Supply to get some gear. I picked up my obligatory “Deadliest Catch” shirt and hat as all tourists do here in Dutch Harbor. We made three trips to the airport throughout the day to see if some of the science gear and luggage came, but came back disappointed. On one of our trips to the airport, we had lunch at the airport restaurant. I had Vietnamese Pho, which is a beef noodle soup, but it wasn’t nearly as good as the Pho my wife makes. 🙂 We also drove up the “Tsunami Evacuation Route” to an overlook where we could see all of Dutch Harbor and the town of Unalaska. Later, we drove around Unalaska and stopped to check out some tidal pools on our way back to the Oscar Dyson. In the afternoon, we checked out the World War II museum that was absolutely fascinating! I did not know Dutch Harbor was bombed by the Japanese and that so many American soldiers were stationed in the bunkers surrounding the harbor. For dinner, I had black cod (sablefish) at the Grand Aleutian Hotel. Yummy!
Monday we embarked on our adventure shortly after noon. We had to leave the dock because another ship was scheduled to offload there in the afternoon. The scientists’ equipment arrived on a late Monday morning cargo flight, but they didn’t make it to the ship on time!!! We couldn’t go to sea without them, so we deployed the “Peggy D” to go pick them up and bring them aboard!
Once we had our missing scientists, we left the safety of Dutch Harbor and ventured into open water. On our way, we saw dozens of humpback whales! None of the whales breached (jumped out of the water), but several of them fluked (dove and put their tail out of the water).
We started our day and a half journey to get to the starting point of our survey transects (the end point of last month’s survey). On our trip out, we experienced 6 to 10 ft seas and a 25 knot wind. It was a “gentle” welcome to the Bering Sea, but I struggled to get my sea legs underneath me. Meclizine is great motion sickness medication, but it sure knocked me out. I feel better now that I am not taking anything and am used to the rocking deck. While we made our way to our first transect, we had a couple of emergency drills. Here I am with fellow Teacher at Sea, Johanna, in our immersion suits as we completed our abandon ship drill.
On Wednesday morning, we began our first transect and did our first trawl along the transect (more on that later). I learned how to work in the fish lab collecting biological data on the catch we brought on board. I have been struggling to adjust to both my shift, which is 4am to 4pm, and the fact that the sun sets around 1am and rises at about 7am.
Thursday morning I woke on time and observed the survey scientists and crew deploying the CTD (Conductivity, Temperature, Depth) rosette from the hero deck (on the starboard side).
We also had beautiful clear skies and I was able to see Venus and Jupiter. At sunrise, I saw the GREEN FLASH!!! It was a beautiful start to the day.
We processed one mid-water AWT (Aleutian Wing Trawl) trawl that was all pollock, then switched to the 83-112 bottom trawl net (83 foot long head-rope and 112 foot long foot-rope) and pulled up a lot of jellyfish with our pollock.
Last night, I finally got a really good night sleep! This morning (Friday), I watched the CTD deployment again and learned more about the data being collected (more on this later). No spectacular sunrise this morning as it was the typical gray, foggy weather. I went up and spent some time on the bridge and Chelsea, our navigator/medic, taught me a lot about the instrumentation used for navigating the ship. There sure is a lot of technology on board!!!
From the bridge, we saw a pod of Dall’s Porpoise feeding, splashing around, and moving fast! We processed another AWT trawl of pollock that had quite a few herring mixed in. We traveled further into Russian waters than originally anticipated as we tried to identify the northern boundaries of the pollock population to get the best picture of the entire pollock range. We spotted a huge Russian trawler from the bridge!
We then headed south again towards American waters, but needed to do a quick water column profile test. Since we did not want to stop to drop the CTD again, I got to deploy a XBT (Expendable Bathythermograph)! After all the talk about safety briefings, the use of ballistics, and outfitting me with every piece of safety gear we could muster, I got ready to fire the XBT!!! Turns out, when you pull the firing pin, the XBT just slides out of the tube… no fireworks, no big bang… just a small kurplunk as the XBT enters the water. We all had a good laugh at my expense. See, scientists know how to have fun!
WOW! So I have just scratched the surface of our voyage thus far! Next time, I will give you a snapshot of what life was like aboard the ship.