NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
August 21 – September 2, 2017
Mission: Juvenile Pollock Fishery Survey
Geographic area of cruise: Western Gulf of Alaska
Date: August 24, 2017
Weather Data: 11.5 C, Foggy
Latitude 56 35.5 N, Longitude 153 21.9 W
Science and Technology Log
At each sampling site, we take two types of samples. First, we dip what are called bongo nets into the water off of the side of the boat. These nets are designed to collect plankton. Plankton are tiny organisms that float in the water. Then, we release long nets off of the back of the boat to take a fish sample. There is a variety of fish that get collected. However, the study targets five species, one of which is juvenile walleye pollock, Gadus chalcogrammus. These fish are one of the most commercially fished species in this area. I will go into more detail about how the fish samples are collected in a future post. For now, I am going to focus on how plankton samples are collected and why they are important to this survey.
As you can see in the photos below, the bongo nets get their name because the rings that hold the nets in place resemble a set of bongo drums. The width of the nets tapers from the ring opening to the other end. This shape helps funnel plankton down the nets and into the collection pieces found at the end of the nets. These collection devices are called cod ends.
This study uses two different size bongo nets. The larger ones are attached to rings that are 60 centimeters in diameter. These nets have a larger mesh size at 500 micrometers. The smaller ones are attached to rings that are 20 centimeters in diameter and have a smaller mesh size at 150 micrometers. The different size nets help us take samples of plankton of different sizes. While the bongo nets will capture some phytoplankton (plant-like plankton) they are designed to mainly capture zooplankton (animal-like plankton). Juvenile pollock eat zooplankton. In order to get a better understanding of juvenile pollock populations, it is important to also study their food sources.
Once the bongo nets have been brought back on board, there are two different techniques used to assess which species of zooplankton are present. The plankton in nets #1 of both the small and large bongo are placed in labeled jars with preservatives. These samples will be shipped to a lab in Poland once the boat is docked. Here, a team will work to identify all the zooplankton in each jar. We will probably make it to at least sixty sampling sites on the first leg of this survey. That’s a lot of zooplankton!
The other method takes place right on the ship and is called rapid zooplankton assessment (RZA). In this method, a scientist will take a small sample of what was collected in nets #2 of both the small and large bongos. The samples are viewed under a microscope and the scientist keeps a tally of which species are present. This number gives the scientific team some immediate feedback and helps them get a general idea about which species of zooplankton are present. Many of the zooplankton collected are krill, or euphausiids, and copepods. One of the most interesting zooplankton we have sampled are naked pteropods, or sea angels. This creature has structures that look very much like a bird’s wings! We also saw bioluminescent zooplankton flash a bright blue as we process the samples. Even though phytoplankton is not a part of this study, we also noticed the many different geometric shapes of phytoplankton called diatoms.
Both the scientific crew and the ship crew work one of two shifts. Everyone works either midnight to noon or noon to midnight. I have been lucky enough to work from 6am – 6pm. This means I get the chance to work with everyone on board at different times of the day. It has been really interesting to learn more about the different ship crew roles necessary for a survey like this to run smoothly. One of the more fascinating roles is that of the survey crew. Survey crew members act as the main point of communication between the science team and the ship crew. They keep everyone informed about important information throughout the day as well as helping out the science team when we are working on a sample. They are responsible for radioing my favorite catchphrase to the bridge and crew, “bongos in the water.”
Did You know?
You brush your teeth with diatoms! The next time you brush your teeth, take a look at the ingredients on your tube of toothpaste. You will see “diatomaceous earth” listed. Diatomaceous earth is a substance that contains the silica from ancient diatoms. Silica gives diatoms their rigid outer casings, allowing them to have such interesting geometric shapes. This same silica also helps you scrub plaque off of your teeth!