Tag: groundfish survey

NOAA TEACHER AT SEA
STEVEN WILKIE
ONBOARD NOAA SHIP OREGON II
JUNE 23 — JULY 4, 2011

Mission: Summer Groundfish Survey Geographic Location: Northern Gulf of Mexico Date: July 3, 2011 Ship Data

Science and Technology Log

One of the first expeditions devoted to the study of the world’s oceans was that of the H.M.S. Challenger.  This voyage covered a distance of more than 68,000 nautical miles.   Although other expeditions prior to the Challenger expedition would periodically collect data about the ocean environment, none were devoted solely to the exploration of the chemical, biological and physical attributes of the oceans.

If you have read my previous posts, you know how important monitoring the abiotic factors are.  This was no different aboard the Challenger expedition.

And remember it took 23 years to process and publish all of the data, well with the help of computers and the internet, the Oregon II’s data is available in hours.

Although technology plays a pivotal role in collecting and analyzing the data, computers still need to be cross referenced against tried and true scientific processes.  In order to ensure that all of the CTD equipment is accurate, random water samples are pulled using the CTD’s sample bottles.  A chemical titration, known as the Winkler titration is used to determine the amount of dissolved oxygen present in the water samples.

The method for sampling the living organisms along the bottom of the seafloor has not changed much since the Challenger expedition.  Trawl nets are still the name of the game, although the way they are deployed might vary a bit!

Once the catch is on board, the process begins to collect data (remember that is why NOAA is out here) to better understand how populations are changing in order to set catch limits and analyze human impact.  In the day’s of the Challenger expedition, the work of analyzing samples and collecting their would have been done in a lab aboard ship, and we rely on similar if not more automated facilities onboard the Oregon II.  Follow this link to take a virtual tour of the Challenger’s “Wet lab”. The wetlab onboard the Oregon II is where I spend the majority of my 12 hour watch.   It is here that the catch is brought after we bring it on deck, we sort the catch, count and measure a subsample of what is brought on board.  If we had to measure everything that came up with the net we would never get finished.  By taking a subsample we can split the catch into percentages depending on the weight of the entire catch and count a smaller sample of the catch.  This subsample’s diversity can then be used as a basis for the entire catch.  This saves time and effort on our part and still provides an accurate representation of what was in the net.  A few species are selected to be counted in their entirety, that includes all commercially important shrimp (brown shrimp, pink shrimp and white shrimp) and all red snapper.  We will also pull organisms into our subsample that are unique to the catch such as sharks, rays, skates etc.

Now I am not quite sure how the Challenger expedition determined where it would sample and when, perhaps if they saw something interesting they would simply drop their nets in the water, but with the Oregon II, the sampling sites are predetermined and the method to set up those sites is quite sophisticated.  In order to ensure that the cruise covers the majority of the Gulf of Mexico NOAA uses a method known as independent random sampling.  This method uses a computer program to randomly select stations based on depth data, and spatial area.  By choosing random samples independently, the scientists can rest assured that they haven’t purposefully singled out an area with “good fishing” or “bad fishing” and that the data they collect will represent a more accurate count of the actual fish populations in the Gulf of Mexico.