NOAA Teacher at Sea
Aboard NOAA Ship Oscar Dyson
July 23 – August 11, 2012
- Mission: Alaskan Pollock Mid-water Acoustic Survey
Geographical Area: Bering Sea
Date: August 10, 2012
Latitude: 53°54’41″ N
Longitude: 166°30’61″ E
Ship speed: 0 knots (0 mph) In Captains Bay at Dutch Harbor during calibration.
Weather Data from the Bridge
Wind Speed: 17 knots (19.5 mph)
Wind Direction: 184°
Wave Height: 1-2 ft
Surface Water Temperature: 10.2°C (50.4°F)
Air Temperature: 12.5°C (54.5°F)
Barometric Pressure: 1005.9 millibars (0.99 atm)
Science and Technology Log:
Imagine a time when fish surveys could be done through remote sensing, thus eliminating the need to catch fish via trawling to verify fish school composition, length, weight, and age data. During our “Leg 3” of the Alaska Pollock Acoustic Midwater Trawl Survey, we caught, sorted, sexed, and measured 25 tons of pollock! While this amounts to only 0.002% of the entire pollock quota and 0.00025% of the pollock population, wouldn’t it be nice if we could determine the pollock population without killing as many fish?
Introducing the “Cam-Trawl,” a camera-in-net technology that NOAA scientists Kresimir and Rick are developing to eventually reduce, if not eliminate, the need to collect biological specimens to verify acoustic data. Cam-Trawl consists of a pair of calibrated cameras slightly offset so the result is a stereo-camera.
The importance of setting up a stereo-camera is so you can use the slightly different pictures taken at the same time from each camera to calculate length of the fish in the pictures. Eventually, a computer system might use complex algorithms to count and measure length of the fish that pass by the camera. If the kinks are worked out, the trawl net would be deployed with the codend open, allowing fish to enter the net and flow past the camera to have their picture taken before swimming out of the open end of the net. Some trawls would still require keeping the codend closed to determine gender ratios and weights for extrapolation calculations; however, the use of Cam-Trawl would significantly reduce the amount of pollock that see the fish lab of the Oscar Dyson. On this leg of the survey, the NOAA scientists installed the Cam-Trawl in a couple of different locations along the trawl net to determine where it might work best.
Below are some photos taken by Cam-Trawl of fish inside the AWT trawl net. Remember, there are two cameras installed as a stereo-camera that create two images that are taken at slightly different angles. In the photos below, I only picked one of the two images to show. In the video that follows, you can see how scientists use BOTH photos to calculate the lengths of the fish captured on camera.
Another NOAA innovation using stereo cameras is called “Trigger-Cam.” Trigger-Cam is installed into a crab pot to allow it to sit on the ocean floor. For this type of camera deployment, the NOAA scientists removed the crab pot net so they would not catch anything except pictures.
The real innovation in the Trigger-Cam is the ability to only take pictures when fish are present. Deep-water fish, in general, do not see red light. The Trigger-Cam leverages this by using a red LED to check for the presence of fish. If the fish come close enough, white LEDs are used as the flash to capture the image by the cameras.
The beauty of this system is that it uses existing fishing gear that crab fishermen are familiar with, so it will be easily deployable. Another stroke of brilliance is that the entire device will cost less than $3,000. This includes the two cameras, lights, onboard computer, nickel-metal hydride batteries, and a pressure housing capable of withstanding pressures of up to 50 atmospheres (500 meters) as tested on the Oscar Dyson! Here is a short animated PowerPoint that explains how Trigger-Cam works. Enjoy!
A little fun at sea! We needed to do one last CTD (Conductivity, Temperature, Depth), and decided to lower the CTD over deep water down to 500 meters (1,640.42 ft)! Pressures increases 1 atmosphere for every 10 meters in depth. At 500 meters, the pressure is at 50 atmospheres!!! We wondered what would happen if… we took styrofoam cups down to that depth. We all decorated our cups and put them in a net mesh bag before they took the plunge. Here is a picture showing what 50 atmospheres of pressure will do to a styrofoam cup!
We missed the Summer Olympics while out on the Bering Sea. T-T We did get in the Olympic spirit and had a race or two. Here is a little video in the spirit of the Olympics…
All for now… We are back in Captains Bay, Dutch Harbor, but are calibrating the hydroacoustic equipment at anchor. Calibration involves suspending a solid copper sphere below the ship while the NOAA scientists check and fine-tune the different transducers. This process will take about 7 hours! We have been out at sea for 3 weeks, are currently surrounded by land, but must wait patiently to finish this last and very important scientific task. If the calibration is off, it could skew the data and result in an inaccurate population estimation and quotas that may not be sustainable! This Landlubber can’t wait to have his feet back on terra firma. The thought of swimming crossed my mind, but I think I’ll wait. Then we will see if I get Land Sickness from being out at sea for so long…