Leg II: There’s a lot more going on than just trawling
Greetings from the NOAA Ship Henry B. Bigelow! Leg II of the NEFSC Spring Bottom Trawl left Newport, RI on Tuesday, March 28th. We made our way South to pick up where Leg I left off.
While this trip is labeled as a bottom trawl survey, there is a lot more going on than just trawling. This ship conducts a lot of exciting science: collecting hydrographic data about the physical characteristics of the water using on-board sensors and special sampling devices, using fine-meshed bongo nets to collect plankton, and of course examining the fish and other marine life that comes up in the trawl. The Bottom Trawl Survey is definitely an ecosystem survey, designed to capture all aspects of the marine environment and ecology.
As an ecosystem modeler, I am very interested in how the data is collected out here and ultimately analyzed back on land. The most basic of fish data that we collect is weight per tow. Each tow is separated by species and then weighed. This information is important so we can get a relative sense of the size of the various populations. From there we take individual length data on most species. Some things are sent back to the lab and counted/measured there.
Just as important as these basic metrics is the biological sampling that we conduct. For some species a subsample of the catch is selected for further study. We determine the sex and maturity of the fish to get information on spawning in a population. We examine their stomach contents to learn more about predators and prey. We also age them using a variety of techniques.
The most common way to age a fish is to use their ear bones or otoliths. This technique works similar to aging a tree. Seasonal changes in a fish’s growth pattern create rings or annuli. Each year a new ring is created. At sea we remove the ear bones and send them back to land. Each species requires some processing of the ear bones before an age reader can count the rings.
The end result is we have an age structure of the population and can track how each year’s cohort is growing and, along with the other data we’ve collected, help forecast sustainable catch levels for the future.
Sean Lucey, ecosystem modeller
Aboard the NOAA Ship Henry B. Bigelow