7/25/2013: Ship's business

This was another pretty slow day of trapping. There just wasn’t a whole lot of habitat around for us to sample in this area, so we didn’t catch too many fish. A couple of items of note happened today, however. Every vessel at sea is required to conduct emergency drills once a week. Some ships make them a surprise for the crew. This ship lets everyone know that there will be a drill. However, the type & intensity of the drill varies. On a research vessel like this one, there is plenty of crew so that the science party’s job is to stay out of the way in the event of an emergency, so we were holed up in the ship’s lounge throughout today’s drills. However, the ship’s crew practiced for an oil leak on the vessel that turns into a fire. Everyone went to their assigned stations, broke into their teams and practiced what they would do in the event of a fire. They even got out the pumps that would help get water out of the boat if the ship lost power. 

After we had hauled in all of the traps, we started transiting to our next mapping location. It is about 50 miles Southeast of where we had been today, so the steam is several hours. On the way we passed by a weather buoy, so most of the ship’s company was out on deck with fishing lines in the water. Many types of pelagic fish like to gather around buoys, so everyone wanted to catch something big. Unfortunately, the only thing we caught were two barracudas. The teacher from Illinois was pretty excited about it. They were the first ocean fish he’d caught on hook-and-line.

CTD ready for deployment

XBT launch

In addition to capturing fish & taking their picture, we use two different devices to learn about the physical characteristics of the area, such as temperature, salinity, etc. The device we use during the day is called a CTD (stands for conductivity, temperature & depth meter). It is a complex electronics package which the ship lowers over the side while we are stationary. It sends back information to the ship about not only  conductivity (salinity), temperature, and depth, but also the amount of phytoplankton in the area, silt in the water column, and other parameters. These can be incorporated into the analyses of fish populations to account for changes in numbers. The second instrument used to sample the water is the XBT(expendable bathythermograph). This is a much less sophisticated & less costly piece of equipment. It gives a lot less data, only depth and temperature. However, the advantage of an XBT is that it the ship doesn't have to slow down in order to deploy it. XBTs are deployed a few times each night during mapping operations. Sound moves at slightly different speeds based on the temperature of the water, so the mapping crew has to know what the temperature of the water is so that they can get an accurate picture of the bottom. An XBT basically consists of a long piece of copper wire which is attached to the ship & thrown toward the bottom of the ocean. As it falls, it transmits the temperature of the water back to the ship. Once it reaches the bottom, the wire is broken. The first few days of the trip the mapping crew liked to play up how exciting "launching" an XBT was & got newbies super into it. It was a good joke to play on people, because it really is a very anti-climactic event. But it is cool to think we can find out the temperature of the water all the way to the bottom while we are moving at 9 knots & using nothing but a little piece of copper.