They are transiting south now and will resume running acoustic transects on Saturday. Everyone is excited to get back to science operations and the crew are particularly excited to start trawling again as they all love to go fishing! Trawling is conducted to validate the acoustic sign to determine if it is hake or something else that is causing the type of backscatter sign observed on the acoustic data. Trawling also helps the scientists learn the size and age-class of the hake forming the aggregation in order to track year-classes of hake in the survey area and from survey to survey.
Trawling is done with a type of midwater trawl called an Aleutian Wing Trawl, or AWT. The AWT does a really good job at fishing aggregations found in the midwater or even near the bottom. The crew are very skilled at maintaining the trawl not only just above bottom (when the fish school is aggregated there), but also at a “target depth” when the fish school is located higher up in the water column. After the trawl comes aboard, the wet lab biologists process the catch to determine the composition of the species caught, weights and counts, and some intensive biological sampling. The biological sampling includes taking lengths, weights, ages, stomach contents, and visual maturity estimates of a number of hake. The lengths are used to scale the acoustic backscatter to hake abundance, while the other measures are used to characterize the stock as a whole. Everyone is looking forward to doing more great science on Leg 2!
