NOAA Teacher at Sea
Erica Marlaine
Aboard NOAA Ship Oscar Dyson
June 22 – July 15, 2019
Mission: Pollock Acoustic-Trawl Survey
Geographic Area of Cruise: Gulf of Alaska
Date: June 28, 2018
Weather Data from the Bridge:
Latitude: 58º 28.54 N
Longitude: 154º 46.05 W
Wind Speed: 16.8 knots
Wind Direction: 190º
Air Temperature: 11º Celsius
Barometric Pressure: 102
Science and Technology Log
Scientists aboard NOAA Ship Oscar Dyson are estimating the numbers and biomass of walleye pollock in the Gulf of Alaska. They use acoustics (sound data) to help them do this.
Acoustic representation of fish in an area
Echo sounders send an acoustic signal (ping) into the water. The sound bounces off objects that have a different density than the surrounding water (such as the swim bladder in a fish) and returns back to the echo sounder. Using the speed of sound, this technology can determine how deep the fish are in the water column.
How much sound each object reflects is known as the target strength. The target strength is dependent upon the type of fish and the size of the fish. A bigger fish will give off more of an echo than a small fish will. A fish’s swim bladder is primarily what reflects the sound. Smelt and krill do not have swim bladders. As a result, they do not reflect as much sound as a pollack would. Even though a big fish gives off more sound energy than a small fish of the same species, it is possible that a return echo could indicate either one big fish or several smaller fish clumped together. A big fish of one species could also give off similar sound energy to a big fish of a different species. For that reason, actual fish are collected several times a day in the nets described in a previous blog.
From a net sample, scientists determine the number of each species in the catch as well as the length and weight of individuals of each species.
Additionally, scientists also determine the sex and age of the pollock. The catch data is used to scale the acoustic data, which in turn allows scientists to estimate how many pollock there are of various size and age groups in a given area. These numbers help scientists determine the sustainability of the pollock population, which in turn allows the North Pacific Fishery Management Council to set catch quotas.
Krill Fun Facts:
Krill (aka euphausiids) are small crustaceans (a couple of millimeters long) of the order Euphausiacea. The word “krill” is a Norwegian word meaning “a small fry of fish.” Krill are found in every ocean and are a major food source. They are eaten by fish, whales, seals, penguins, and squid, to name a few. In Japan, the Phillipines, and Russia, krill are also eaten by humans. In Japan, they are called okiami. In the Phillipines and Russia, they are known as camarones. In the Phillipines, krill are also used to make a salty paste called bagoong. Krill are a major source of protein and omega-3 fatty acids.
Personal Log
People often refer to New York as the city that never sleeps. The same can be said for the NOAA Ship Oscar Dyson. Life onboard the Oscar Dyson carries on 24 hours a day, 7 days a week. There is never a time that the ship is not bustling with activity. Everyone on the boat works 12-hour shifts, so someone is always working while others are sleeping (or doing laundry, exercising, or watching a movie in the lounge before they go to sleep.) Most people on the boat work either the noon to midnight shift or the midnight to noon shift. However, the science team works 4 a.m. to 4 p.m., or 4 p.m. to 4 a.m. I am in the latter group. It was easier to get accustomed to than I had imagined, although it is sometimes confusing when you look at your clock and wonder whether it is 5 a.m. or 5 p.m. since the sun is shining for most of the day. Kodiak has only 4-5 hours of darkness now, and the sun sets at approximately midnight. Therefore, it does not really feel like nighttime for much of my shift.
