Trawling for Science
Originally posted on Deepwater Canyons:
by S.W. Ross (UNCW, 7 May 2013)
On this cruise the ROV Jason II is our main science sampling tool; however, underwater vehicles cannot stay on the bottom indefinitely nor can they collect every type of sample needed. We use a variety of gear specific to different needs, and many types of nets are included in our arsenal of sampling gear. On this cruise we are using a bottom otter trawl to collect fishes and invertebrates. This is a small net (16 ft wide) that is held open by water pressure on otter doors (rectangular wood boards weighted with steel). Most of this sampling takes place at night after ROV operations, but if the weather is too rough for the ROV, we will trawl during the day, sometimes in very deep water (1670 + m). All of our tows are only 30 min, and this matches our data over the last 12 years, yielding a consistent data set for us to compare samples from the Gulf of Mexico to the Mid-Atlantic. While the tows are short, the actual time to conduct deep-water tows can be long because the amount of wire we must let out is 2.5-3 times the water depth. For deep trawls we have out 4,000 m of wire; thus, one tow will require 5 hours of vessel time.