Mission: Walleye Pollock Survey Geographical Area of Cruise: Gulf of Alaska Date: 8/5/13
Weather Data from the Bridge (as of 17:00 Alaska Time): Wind Speed: 9.54 knots
Temperature: 15.7 C
Humidity: 83 %
Barometric Pressure: 1017.9 mb
Current Weather: The winds have decreased and we are not moving as much. The weather report calls for an increase to the winds with 7 ft swells on Wednesday. But maybe it will die down before it reaches us.
Science and Technology Log:
We only will fish during daylight hours. The sun is now setting before 10:00 pm and rising around 5:30 am. And even though we are not fishing between sunset and sunrise, science continues. At nightfall, we break transect and Jodi begins her data collection.
The Sustainable Fisheries Act mandates an assessment of essential fish habitat. This is in conjunction with stock assessments of groundfish. Jodi’s research involves integrating multibeam accoustic technology to characterize trawlable and untrawlable seafloor types and habitat for managed species.
A bottom trawl survey is conducted every other year in the Gulf of Alaska. The goal is to better identify seafloor types using multibeam acoustics. This would help improve groundfish assessment, and limit damage to habitat and trawling gear.
The Gulf of Alaska survey area is divided into square grids.
On this cruise we are conducting multibeam mapping in trawlable and untrawlable grid cells. A grid cell is divided into 3 equidistant transects for a multibeam survey. Jodi directs the ship to follow these smaller transect lines. While the ship is following the transects lines, the multibeam sonar is active and data is collected.
The SIMRAD ME70 is the multibeam sonar that Jodi is using for her research. There are 6 transducers on the ship that will send out a fan of 31beams of varying frequencies. The strength of their return (backscatter) can be analyzed for sea floor type. Looking at the diagram below, you can see the differences in backscatter clearly in the range of 30 to 50 degrees (away from straight down).
Silts will have a very weak backscatter and rock will have a strong backscatter.
After the transects are completed, Jodi and Darin complete 1 – 3 camera drops to record visually how the seafloor appears. This camera below will be lowered to the ocean floor and video footage will stream to the computer for 10 minutes. Then the camera is brought up.