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EcoFOCI Cruise - Post 3

June 06, 2022

EcoFOCI’s spring mooring cruise departed Dutch Harbor on May 10. This annual survey provides baseline fisheries & oceanographic data to support ongoing management of our nation's fisheries and marine life in the Bering Sea & rapidly changing U.S. Arctic.

Deploying the bongo nets over the starboard of the ship. Recovering bongo nets. Why are they called bongo nets? They look like a set of bongo drums!

Side-Ops Around the Clock

Continuing on from Blog 2, the mooring operations are only part of the story. At every mooring site and in between, the Side-Ops Team springs into action. These folks make up two groups that are working in opposite 12-hour shifts, so that either team is ready to sample whenever the ship is on station.

CTD rosette being craned over the side an into the ocean at night.
Night deployment of the CTD rosette.

Their main tasks are to launch and recover the CTD and Bongo nets, and to process the samples that are collected. The CTD is the primary tool for determining essential physical properties of sea water that helps to understand how the oceans affect life.

A CTD measures Conductivity, Temperature, and Depth and it’s affectionately called a “rosette” because it has the symmetry of a rose flower. Around the outside are up to 12 cylindrical tubes called Niskin bottles, which are open when the CTD is deployed. The CTD is lowered to 5 meters above the bottom, where the first cylinder is closed remotely from the ship’s Dry Lab—capturing the water at that depth. As the CTD is brought back to the surface, it’s stopped at specified depths (for the EcoFOCI survey, these are at 50m, 40m, 30m, 20m, 10m, and 1m-3m beneath the surface) where another bottle is closed. When retrieved to the deck, each bottle contains a water sample at a unique depth.

CTD rosette secured by deckhands as it's brought back onto deck.
Recovering CTD to deck after sampling in the late evening.
Collecting water sample from Niskin bottle on the CTD.
Collecting samples of water from the CTD rosette.

The CTD also transmits real-time information back to the ship. In the Dry Lab, scientists monitor temperature, dissolved oxygen, salinity, PAR (Photosynthetic Active Radiation, aka. sunlight), and fluorescence throughout the water column, and couple that with atmospheric measurements by the ship at the surface.

The crew also attached a camera towards the bottom of the CTD. It photographs plankton throughout the dive, and these images will be analyzed after the survey to understand what floating creatures are living at what depths at this site. This new technique rapidly assesses zooplankton presence and relative abundance at depth by coupling images of plankton with machine learning (learn more at this link).

Scientist point at computer screens that show real-time data coming from CTD.
Scientists monitoring the CTD from the Dry Lab.
Side by side images of the camera attached to the CTD, one wide shot, one close up on the lens.
On the left is the attached near the bottom of the CTD that photographs plankton throughout the dive. On the right is a close up image of the camera magnifying lens as the flash is firing.

These Niskin bottles collect up to 10-liters of water, which is just over 2.5 gallons, so there’s a lot we can do with these samples. One member of the team measures dissolved oxygen and ocean acidification. Another pair runs samples through different sized filters to separate phytoplankton of different sizes. And as the team gathers each of these samples, they rinse the collection vials out several times with the collected seawater to be sure that those bottles contain a true representation of that particular depth.

Woman pouring water sample into a filter apparatus.
Processing water samples in the wet lab.

Immediately following the CTD launch and recovery, the Bongo net is deployed. You’ll notice two pairs of different sizes of openings. The nets that trail behind them are different too. The larger ones have a 60cm opening with a mesh size of 505 microns, while the smaller ones have a 20cm opening and a 153-micron mesh size. This allows the scientists to target different sized zooplankton from the size of a grain of sand to larger than a grain of rice. The bongo nets are towed starting at 5 meters above the bottom all the way to the surface, which can take anywhere from 5 to 17 minutes from deployment to recovery.

Deploying the bongo nets over the starboard of the ship.
Recovering bongo nets. Why are they called bongo nets? They look like a set of bongo drums!

As the CTD crew focuses on phytoplankton (microscopic plants), the Bongo Net crew focuses on zooplankton (floating animals that are often larval stages of fish, crabs, but also tiny animals like copepods that are important prey for young fish, whales, and more). So, once the nets are back on board, they try to further isolate the zooplankton.

Team sprays down the bongo nets to push sample into the sample jar at the end of the net.
Rinsing the Bongos nets so that everything inside the net ends up in the cod-end (that cylinder at the bottom of the net).
Spraying water over sample on a fine wire mesh sieve to isolate the zooplankton
Separating out the zooplankton using sieves.
Closeup on 500 micron sieve with zooplankton, including krill
Sieve full of zooplankton in the sieve, including krill.

Each individual sample is filtered using sieves, which have specific sized openings that match the bongo nets. After some rinsing with seawater, much of the phytoplankton is washed through the sieve, and you’re left with zooplankton samples that are analyzed back at the Seattle lab. Some samples are also viewed under the microscope at sea, to immediately monitor what’s present at that site and to select individual specimens for research projects that colleagues are working on.

Scientist at microscope with camera connected to computer. She points at a pollock egg shown on screen.
Pollock egg shown on a computer screen through the microscope’s camera.

Each station takes at least a half-hour to process all the samples and typically stations are only about 45-minutes apart, so the scientists are working non-stop. See below to revisit the original survey map. You’ll notice all the blue and yellow dots. The blue dots correspond to CTD & Bongo stations, while the yellow dots are CTD-only stations, and most of those lie along the 70-meter isobath. If you remember from Blog 2, that’s a line where the depth remains at 70 meters, or 230 feet.

Map of eastern Bering Sea showing sample stations.
Map showing overall working area for 2022 Spring Mooring Survey.

Additionally, around the mooring sites (M2, M4, M5, and M8) you’ll see a box of blue dots, which are designed to get more information to couple with the mooring data. There’s also a big box around Unimak Pass, serving as one of the main passageways between the Bering Sea and the North Pacific Ocean, and an important spawning ground for commercially important fish species such as Pacific cod, Alaska pollock, and flathead sole.

Two Pacific cod hover over a baited cage.
One year-old Pacific cod inspecting a baited camera station.

All of these data, including information on phytoplankton and zooplankton productivity and oceanographic conditions, are critical to help us understand any changes that occur in the ocean, and how that might affect the resources that we depend on. We also strive to understand all the different life stages of seafood that helps sustain our health and economies. A higher abundance of fish eggs today could be good news for our fisheries in years down the road, and help us set quotas appropriately. Likewise, there may be some years that we have to cut back on our catches if conditions prevent certain life stages of a species to thrive.

The interdisciplinary approach of the EcoFOCI survey is extremely valuable for all of the above. And that’s not all that’s going on with these biannual surveys.

Check out the 4th and final blog in this series!

Previous: EcoFOCI Cruise - Post 2 Next: EcoFOCI Cruise - Post 4

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