NOAA Teacher at Sea
Jessica Cobley
Aboard NOAA Ship Oscar Dyson
July 19 – August 8, 2019
Mission: Midwater Trawl Acoustic Survey
Geographic Area of Cruise: Gulf of Alaska (Kodiak to Yakutat Bay)
Date: 8/6/2019
Weather Data from the Gulf of Alaska: Lat: 58º 44.3 N Long: 145º 23.51 W
Air Temp: 15.9º C
Personal Log
Currently we are sailing back across the Gulf of Alaska to the boat’s home port, Kodiak. I think the last few days have gone by quickly with the change of daily routine as we start to get all the last minute things finished and gear packed away.
Since my last post, the definite highlight was sailing up to see the Hubbard Glacier in Disenchantment Bay (near Yakutat). WOW. The glacier is so wide (~6miles) that we couldn’t see the entire face. In addition to watching the glacier calve, we also saw multiple seals sunbathing on icebergs as we sailed up to about a mile from the glacier.
We spent a few hours with everyone enjoying the sunshine and perfect view of the mountains behind the glacier, which form the border between the U.S. and Canada. We also had a BBQ lunch! Here are a few photos from our afternoon.
Another surprise was showing up for dinner the other night to find King Crab on the menu. What a treat! Most people are now trying to get back on a normal sleeping schedule and so mealtimes are busier than usual.
Lastly, the engineering department was working on a welding project and invited me down to see how it works. On the first day of the trip I had asked if I could learn how to weld and this was my chance! They let me try it out on a scrap piece of metal after walking me through the safety precautions and letting me watch them demonstrate. It works by connecting a circuit of energy created by the generator/welding machine. When the end you hold (the melting rod) touches the surface that the other end of the conductor is connected to (the table) it completes the circuit.
Scientific Log
Before making it to Yakutat we fished a few more times and took our last otolith samples and fish measurements. Otoliths are the inner ear bones of fish and have rings on them just like a tree. The number and width of the rings help scientists calculate how old the fish is, as well as how well it grew each year based on the thickness of the rings. In the wet lab, we take samples and put them in little individual vials to be taken back to the Seattle lab for processing. Abigail did a great job teaching where to cut in order to find the otoliths, which can be tough since they are so small.
Another important piece of the survey is calibrating all of the equipment they use. Calibration occurs at the start and end of each survey to make sure the acoustic equipment is working consistently throughout the survey. The main piece of equipment being calibrated is the echosounder, which sends out sound waves which reflect off of different densities of objects in the water. In order to test the different frequencies, a tungsten carbide and a copper metal ball are individually hung below the boat and centered underneath the transducer (the part that pings out the sound and then listens for the return sound). Scientists know what the readings should be when the sound/energy bounces off of the metal balls. Therefore, the known results are compared with the actual results collected and any deviation is accounted for in the data accumulated on the survey.
After calibration, we cleaned the entire wet lab where all of the fish have been processed on the trip. It is important to do a thorough cleaning because a new survey team comes on board once we leave, and any fish bits left behind will quickly begin to rot and smell terrible. Most of the scales, plastic bins, dissection tools, nets, and computers are packed up and sent back to Seattle.
Did You Know?
Remember when you were a kid counting the time between a lightning strike and thunder? Well, the ship does something similar to estimate the distance of objects from the ship. If it is foggy, the ship can blow its fog horn and count how many seconds it takes for the sound to be heard again (or come back to the boat). Let’s say they counted 10 seconds. Since sound travels at approximately 5 seconds per mile, they could estimate that the ship was 1 mile away from shore. We were using this method to estimate how close Oscar Dyson was from the glacier yesterday. While watching the glacier calve we counted how many seconds between seeing the ice fall and actually hearing it. We ended up being about 1 mile away.
Cheers, Jess
