September 18th: A Preview of Night Operations
Written By Dan Suthers September 18-19, 2004
Today I spent most of the day in the dry lab writing, organizing photographs, and working on the web site, while the REA and Towboard teams continued to survey fish and benthic communities and habitat, and the Mooring team retrieved and deployed sensors. In the dry lab and on deck, the Night Operations team worked with our Electronics Technician to prepare for tests this evening. The photographers had spent the previous night on Tern Island to photograph baby sea turtles when they emerged from their nests early this morning. (See the NOWRAMP 2002 story about turtles.)
From my point of view as shipbound staff, the real action started in the evening, just after dinner. I was informed that the Fish Team was in the process of performing dissections, and went out to the lower aft deck to photograph them. Randy Kosaki had collected fish with a spear (he has a permit to take limited samples for research purposes). He was dissecting fish to obtain tissue samples for carbon isotope analysis. This anlaysis will help determine the extent to which benthid algae versus planktonic algae are supporting the food chain: each of these forms of algae has different carbon isotope ratios. Darla White, who works with Dr. Michael Parsons at the University of Hawai`i in Hilo, was removing fish intestines to be checked for the dinoflagellates that cause ciguatera poisoning, and tissues to be tested for the ciguatera toxin. They are sampling both herbivores and carnivore fish to determine whether the dinoflagellates are in the NWHI and to what extent the toxin works its way up the food chain. As they worked on the fish, Randy munched on some chips, putting a different spin on the phrase "fish and chips."
Just behind this scene, Jim Bostic was refilling air tanks. Jim is the ship's Chamber Operator, and is also responsible for the decompresssion chamber we carry on board in case of a dive accident. The tank filling machine takes air from the outside and compresses it, and then circulates it through a membrane with tiny tubes through which oxygen can pass more easily than nitrogen. By this process, the oxygen content of the air is increased from 21% to 32% before it is put into the tanks. It is important to know the concentration of oxygen in your tanks, as this affects how long you can stay down. Therefore divers always check their tanks with a sensor before loading them in the morning.
On the rear of the aft deck, a motor started up: deck hands were testing an outboard motor. On the starboard side of the aft deck, Scott Ferguson prepared a device called the TOAD, and others prepared the CTD device (both are explained below). Up in the wet lab, the Benthic team worked on their samples, and the photographers prepared for their evening session capturing invertebrates on film. In the dry lab, Casey prepared towboard cameras for tomorrow
Before dusk a long evening of night operations began.
First the Conductivity, Temperature and Depth (CTD) sensor device was prepared, lifted into the water by a crane, and gradually lowered to 500 meters depth by a high-tech winch that can measure depths precisely. Conductivity is an indicator of salinity: water is more conductive if it has more salt dissolved in it. Essentially the CTD is measuring salinity and temperature at different depths. Water of different densities tends not to mix, so when you pass through a change in density you are probably entering a different current. People who study currents will do multiple measurements in a grid over a wide area, but the NWHI team is using it to monitor ecosystem health, so our measurements are patterned at different depths around reefs. The CTD makes these mesurements continuously as it is lowered and raised (see data display). Usually the measurements taken on the way up are used. As it was raised, the CTD device was stopped periodically to trigger water sample collectors.
After dark, the Towed Optical Assessment Device (TOAD) was set loose. This device, which bears no resemblance to an amphibian, consists of a video camera and lights on a handmade frame designed to be towed just above the bottom of the surface. Although more sophisticated versions are available, our on-board TOAD is a trusty old handmade version; beat up and improbable looking for a scientific instrument, yet it does the job well.
TOAD data is used to certify bioacoustic habitat sensing that will take place on a future expedition. Specifically, the TOAD videos tell us what is actually on the bottom: sand, rubble, or live coral, but does so only in the few locations we can actually tow the device over. Acoustic sensing will be used to cover a larger region, but we need to know how to interpret the acoustic data by comparing it to the visual observations taken by the TOAD. (The concept is similar to ground-truthing interpretations of satellite photographs by selectively checking locations on the surface.)
When the TOAD camera went into the water and its light was turned on, we were struck by how much "stuff" was floating around in the water. It looked like a green blizzard. As the camera descended we occasionally saw something swim by or follow the camera briefly. Once it reached the bottom, Scott watched the video image from inside the dry lab while radioing instructions to Mark O'Connor, asking him to raise or lower the TOAD a meter as needed to keep it from crashing into the bottom. As the TOAD passed over sand, the impression that we were in an underwater blizzard was strong, but when we reached coral it was clear this was no artic environment. Beautiful branching, plate and encrusting corals passed by, while occasional fish darted away, or simply "slept" on the bottom. Twice we saw a shark swim by, perhaps opportunistically interested in the fish attracted to the light.
These observations just give us a taste of all the operations taking place on the boat each day. Once we (this writer as well as you the readers) have a better picture of the various activities, we will delve into details of the science behind them.
Note: On October 4th I added an article on reef oceanography that explains the CTD and related measurements.