Photo story: Virtually cruise aboard a NOAA ship for a fish trawl survey

See how scientists collect fish science data at sea

May 25, 2016

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NOAA Ship Oscar Dyson steers through open water in the Gulf of Alaska. (Image credit: NOAA)

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Trawling a net behind a boat is a longstanding way of catching fish at sea. NOAA research vessels use trawling for many of the agency's fisheries surveys every year, providing important data that have helped the U.S. become a model of sustainable fisheries. This series of photos shows how a trawl operation collects those data for scientists and fisheries managers. The information plays key roles in fishery stock assessments and ecosystem science studies.

Staging the net for deploymentCrew on the Oscar Dyson prepare to deploy the trawl net on the back deck while the ship adjusts its heading based on the wind and sea conditions. Once in the water, an acoustic sensor between the two white floats monitors the net’s underwater position. (NOAA/C.Kliewer)
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Hauling the net and its catch onboardAt the end of the trawl, the lead fisherman (far left) operates the winch controls to slowly haul the net on board. Deck crew members keep the net aligned with the large reel in the foreground. (NOAA/C.Kliewer)
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Emptying the netWith the entire catch funneled inside, the end of the net gets suspended so the deck crew can empty it into bins. (NOAA/C.Kliewer)
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Sorting and countingCrew carry the bins into a lab and empty them onto a conveyor belt, where the scientists can identify, sort and count the fish and other specimens. In this case, a portion of the trawl yielded a handful of adult pollock and assorted jellyfish. (NOAA/C.Kliewer )
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Recording data, even for the little fishCareful sorting reveals juvenile fish and other small species that were mixed in with the larger fish. The scientists make sure to record these data as well. (NOAA/C.Kliewer)
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Taking water chemistry measurementsAt each trawl location, the crew and scientists measure conductivity (used to determine salinity of the water), temperature, and depth by lowering this rosette of instruments into the water. For more detailed analyses back in the lab, each of the large gray bottles captures a water sample at a different depth. The data provide scientists important information about the local aquatic environment. (NOAA/C.Kliewer)
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Collecting plankton — the base of the food webThe ship also tows a plankton net at each location. Called a “bongo net” because it resembles a drum set, it collects plankton — tiny animals like fish larvae and krill that live in the water — which are too small to get caught in the trawl net. Plankton are an important source of food for many fish and whales, so plankton samples tell scientists about what food is available in the area. (NOAA/C.Kliewer)
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One trawl operation complete — off to sample another areaNot far from the mountainous coast of the Alaskan peninsula, the NOAA Ship Oscar Dyson travels to its next location to collect samples in another area. (NOAA/C.Kliewer)
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