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 29, 2017
Weather Data: 10.2 C, rainy/stormy
Latitude: 59 20.0 N, Longitude: 152 02.5 W
Science and Technology Log
The main focus of this survey is to gather information about juvenile walleye pollock, Gadus chalcogrammus. Juvenile pollock less than 1 year of age are called young-of-the-year, or age-0 juveniles. Age-0 walleye pollock are ecologically important. Many species of birds, mammals and other fish rely on them as a food source. Adult pollock have a high economic value. Pollock is commercially fished and commonly used in fish sticks and fish and chips. This study is interested in learning more about the size of current juvenile pollock populations, where they occur, and how healthy they are.
In order to collect a sample, a trawl net is lowered into the water off of the back of the ship. The deck crew and bridge crew work together to release the right amount of wire and to drive the ship at the right speed in order to lower the net to the desired depth. The net is shaped like a sock, with the opening facing into the water current. In order to keep the mouth of the net from closing as it is pulled through the water, each side is connected to a large metal panel called a “door”. As the doors move through the water, they pull on the sides of the trawl net, keeping it open. When the doors are ready to be put in the water, the fishing officer will instruct the winch operator to “shoot the doors”!
Sensors help monitor the depth of the upper and lower sides of the net and relay a signal to computers on the bridge, where the data can be monitored.
Once the net is reeled in with a large winch, the catch is placed on a sorting table, in a room just off of the back deck called the fish lab. Here, the science team works to sort the different species of fish, jellyfish, and other kinds of marine animals that were caught.
Juvenile pollock are sorted into their own bin. If it is a small catch, we weigh, count, and measure the length of each one. However, if it is a large catch, we take a smaller sample, called a subsample, from the whole catch. We use the weight, lengths, and count of animals in the subsample to provide an estimate count and average size of the rest of the fish caught at that station, which are only weighed. This information is compiled on a computer system right in the fish lab.
The focus of this study is juvenile pollock, but we do catch several other species in the trawl net. The presence of other species can provide information about the habitats where juvenile pollock live. Therefore, data from all species collected are also recorded.
A small sample of juvenile pollock are frozen and saved for further study, once back on land. These fish will be analyzed to determine their lipid, or fat, content and calorie content. This data reveals information about how healthy these fish are and if they are getting enough food to survive through the cold Alaskan winters.
Other agencies within NOAA also conduct scientific surveys in this area. These studies might focus on different species or abiotic (non-living) properties of the Gulf of Alaska marine ecosystem. The data collected by each agency is shared across the larger NOAA organization to help scientists get a comprehensive look at how healthy marine ecosystems are in this area.
As we move from one station to the next, I have been spending time up on the bridge. This gives me a chance to scan the water for sea birds and marine mammals, or to just take in the scenery. Other members of the crew also like to come up to do this same thing. I have really enjoyed having this time every day to share in this activity (one of my favorite past-times) with other people and to learn from them how to identify different species.
Did You Know?
You can find the exact age of many fish species by looking at a bone in their ears! Fish have a special ear bone, called an otolith. Every year, a new layer will grow around the outside of this bone. As the fish ages, the otolith gets larger and larger. Scientists can find the exact age of the fish by cutting a cross section of this bone and counting the rings made from new layers being added each year.