NOAA Teacher at Sea
Onboard Research Vessel Hugh R. Sharp
June 8-19, 2009
Mission: Sea Scallop Survey
Geographical Area: New England Coast
Date: June 15, 2009
Weather Data from the Bridge
Wind: Speed 6.8 KTS, Direction 65.7 degrees
Barometer: 018 millibars
Air temperature: 11.33 0C
Seas: 2-3 ft.
Science and Technology Log
We had to change out the dredge during my last watch. Actually, I watched while the crew did the dangerous work. We have been working in an area with a rocky bottom and the rocks caused substantial damage to the netting in the dredge. Fortunately, we are carrying four dredges plus spare netting. The crew put a new dredge into operation right away so that we didn’t lose too much time. Geoff, our watch chief, directed the installation of the new mesh into the first dredge.
The scallop dredges we use are eight feet wide. Commercial dredges are sixteen feet wide. The basic design is the same for each. The mouth of the dredge is a welded steel rectangular frame, with the height about one foot. The bottom of this rectangle is a heavy steel bar, called the cutting bar. This breaks loose organisms from the bottom. A steel plate, called the pressure plate, is welded at an angle across the top of the rectangle. This plate creates a downward swirl of water that directs the organisms into the mouth of the netting. The bag attached to the dredge is made of a net of steel rings. A mesh liner is mounted inside the bag for scientific use. This helps to trap other organisms that make up bottom-dwelling communities. This gives scientists a more complete picture for the survey. Commercial dredges do not use a liner and the rings of the bag are larger. This allows smaller size scallops and other organisms to pass through the bag and remain to help sustain a healthy scallop population.
We have been ‘shadowed’ by another ship, the Kathy Marie for part of the time we have been working. She is carrying a device known as the “HabCam”, short for Habitat Camera. This is an underwater camera system that is towed just over the bottom. It makes a photographic record of still images of the bottom taken at a rate of three per second. The HabCam accumulates data at about three terabytes per day. The Kathy Marie runs over the same area dredged by the Sharp after we move on to the next station. Images from these runs provide scientists with an index of dredge efficiency at capturing the bottom dwellers. Once enough image data has been collected to make useful correlations to dredge data, it might be possible to reduce the number of physical dredge samples taken and use the HabCam to record the community ‘in situ’, that is, in position without disturbance.
I said in an earlier log entry that fish are not my favorite type of organism. Because of this bias, I had been avoiding helping with the fish sorting and identification. After thinking about this for a bit, I decided that I needed to embrace my bias against fish and try to learn something as well as help my colleagues. Besides, how could I face my students without at least making an effort? So, I am trying to learn how to identify these critters. So far, I am pretty good with goosefish, red hake, longhorn sculpin and some of the flounder species.
I wonder how long it will take me to adjust to walking on dry land after being at sea for eleven days. I guess I’ll find out soon enough. I have been trying to read some before going to sleep, but I find that I can do a few pages at best. Hard work, sea air and the rocking motion of our ship make powerful sleep inducers.