NOAA Teacher at Sea
Roy Moffitt
Aboard USCGC Healy
August 7 – 25, 2018
Mission: Healy 1801 – Arctic Distributed Biological Observatory
Geographic Area: Arctic Ocean (Bering Sea, Chukchi Sea, Beaufort Sea)
Date: August 10, 2018
Current location/conditions: mid day August 10
Air temp 45F, sea depth 59 m , surface sea water temp 44F
Catching the Tiny Fish in the Big Sea
For the past two days, I helped out Robert Levine, PhD Student of Oceanography at the University of Washington, working with NOAA Alaska Fisheries Science Center. We sent out a Methot net to catch juvenile fish today. In the below picture, taken yesterday, I am helping Robert assemble the Methot net.
For catching fish a centimeter or two long, the net seems huge. The opening of the net is approximately 2.2 meters by 2.2 meters or 5 square meters. The net itself is approximately 10 meters long. The holes in the net are only 2 mm. This means anything bigger than 2 mm will be caught up in the net.
Before sending the net into the sea Levine takes an echogram survey. He lowers the recorder overboard and the attached cable sends the results back to the computer on board. Two different wavelengths are sent out and bounce off anything in the sea column. The smaller wavelengths will show where any of the smaller fish are hanging out. The results give an accurate depth measurement of the ocean and shows small organisms at about 28 meters in depth. The net is then lowered into the sea and trawled at that depth for about 15 minutes.
My task during the net deployment was to measure the angle of the cable entering the water by using a hand held inclinometer. It is important to keep the angle around 45 degrees to keep the proper depth.
Today was not considered a high population area, but we were still able to catch some fish and more marine life. All contents end up in a canister at the end of the net in a big slurry of sloppy stew. In the picture of the bucket the fish are hidden within moon jellyfish and all the little black dots that are crab megalopa. Crab megalopa is the second life stage of a crab before transformation into juvenile crabs to start their life on the sea floor. For fish today what was caught in the net were juvenile Cod, juvenile flat fish, and Sculpin. (Shown in picture with the round dish.)
The goal of this fish collection is to verify the presence of juvenile fish and better understand the geographic range of fish during their life cycle. The exact identification of each will take some time and many of the tiny fish are frozen and sent out to labs for further identification. Levine will also be releasing several bottom-moored echo sounders during the trip. These instruments will be able to monitor the presence of fish and record that data over the year.
Now and Looking forward
Future specimen collections on this trip will be happening using the Methot net to verify distribution and seasonal movement of fish population in the Chukchi Sea.
My goodness, Roy, this is way above my little brain of understanding! I’m very grateful that you, the US Coast Guard and all the scientists are doing this. I’m sure the information will be helpful, even if I don’t understand it!