NOAA Teacher at Sea
NOAA Ship Oscar Elton Sette
June 12th – June 26th, 2013
Mission: Kona Integrated Ecosystems Assessment http://www.pifsc.noaa.gov/kona_iea/
Geographical area of cruise: The West Coast of the Island of Hawaii
Date: Sunday, June 16, 2013
Current Air Temperature: 78° F
Sea Surface Temperature: 79° F
Wind Speed: 20 knots
All is well on the Sette! Skies have been clear, waters have been relatively calm and the mood onboard has been positive. With the cooperative work of the scientists, the crew’s expert ship handling and Clem and Jay’s fine cooking it has been a very interesting week for me. For years I have taught about physical oceanography with a focus on what we know, not necessarily how we know it. I had a sense of how things were done in general; using sonar and taking samples, but I never understood the details of how we can target specific locations to study in such a vast ocean to get a picture of it as a whole system. In just a few days aboard this research vessel I have been given a look at how ocean science is conducted and how our knowledge about the expansive oceans is built one piece of thoughtful data at a time. In the last week I have learned how a well-organized research plan is executed and have also learned about some of the difficulties of conducting science at sea as well.
Science and Technology Log – Night Trawling
One of my nightly tasks is to help a team of scientists conduct trawls of the mesopelagic zone to identify the organisms that live there. The mesopelagic zone (pictured) is also known as the twilight zone because it is where there is a small amount of sunlight that penetrates the water, but not enough for photosynthesis to occur. If you recall from my last blog, the Sette has an active acoustics team that is using active sonar to identify layers of organisms at specific depths in the water column. During the daytime this layer is too deep for our nets to catch them. But at nighttime this layer migrates up towards the surface allowing us catch them with in a net in a process called a trawl. We do two trawls each night. Before each trawl the acoustics team tells the trawl team the depth of the target layer. The deck crew then deploys a fairly large net down to that depth and drags it through the water to scoop up the organisms that we have targeted. After about an hour of doing this the net is pulled back up to the ship where all the creatures are collected in a bag called a “cod end”. It may sound fairly simple, but this process requires the coordination of many different people as the scientists need to communicate with the deck operations crew, and the deck crew has to work with the captain to ensure that the very long net line hits the target and does not get tangled or damaged in the process. Keep in mind that this is happening at 1:00am with 20 knot winds and 10 foot waves. It is a wonder to see and be a part of this operation.
Once we have collected all of the organisms we move on to sorting the catch. We separate the contents of the net into five main categories and then measure the number, mass and volume of each of the types. Perhaps the most commonly abundant of the groups that we classify are mesopelagic fish, which are dark in color and contain photophores to provide them camouflage in the night. Cephalopods (squid) are also quite common along with gelatinous creatures such as jellyfish and crustaceans over 4cm in length, such as shrimp. The final category of interest to us is the shore-fish, which are juvenile fish that will eventually move more towards the land or reefs once they are bigger. The shore-fish are typically the most beautiful looking of the catch.
Everything that is left over is then lumped into a general category called miscellaneous, which is mainly composed of krill. Some cool stuff we’ve gotten in the bag that don’t really have their own category have been two cookie-cutter sharks, a seahorse and two remoras.
So what does this all have to do with cetaceans? I have yet to mention them in my blogs. By studying the composition of the mesopelagic layer we can better understand the food chain and ecosystem that the whales and dolphins depend on. Next week when we begin actively searching for cetaceans we will be able to better understand their behaviors because we have background data on where their food is, what it is composed of and how it behaves. Hope all is well back on land…
NOAA Teacher at Sea