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Seafloor Characterization of the U.S. Caribbean |
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February 28, 2004
Nancy Foster Mission Cruise Update #8
Seas were calm during the early hours of the 28th, and the SCUBA diving crew once again prepared for their morning dives. Dive locations were scattered all along the mid-shelf Reef (MSR - see previous updates for a description of the MSR); however, unlike previous dives, these were all preformed outside of the boundary of the US National Park Service's Virgin Islands Coral Reef National Monument (VICRNM). The habitats and associated fauna that SCUBA divers encountered here are not afforded the same degree of protection. While it is generally difficult to tell the difference between inside and outside the monument based on the fishes encountered, fishing pressure is noticeably higher outside of the monument.
The pictures above show several stoplight parrotfish (Sparisoma viride) and a smooth trunkfish (Lactophrys triqueter) caught in a trap near one of our dive locations. This trap was fished in a series with several other traps attached to it. For the most part, we saw many of the same fishes as we have seen over the past several days inside the monument. The bi-colored fish below is a curious coney (Cephalopholis fulvus) that decided to pay mission chief scientist Mark Monaco a visit. On his way back up to the boat, mission chief biologist John Christensen encountered a large barracuda (Sphyraena barracuda) circling the divers, always keeping a safe distance from the strange visitors from above.
Once the divers returned to the Foster, it was again time to haul the fish traps that we had set the night before. This was the last set of traps that were to be fished inside of the Monument. Today's haul was the largest yet, with many species represented in the catch. The haul was dominated by French grunt (Haemulon flavolineatum), but also contained several yellow goatfish (Mulloidichtyes martinicus), blue tang (Acanthurus coeruleus), schoolmaster snappers (Lutjanus apodus), and red hind (Epinephelus guttatus) which is shown below. Here you can see NCCOS scientist Alan Friedlander measuring the length of the red hind that will be used to help construct a picture of the age and size-class structure of this species along the MSR. We are again happy to note that all fishes captured in the overnight trap sets were safely released back to the reef below once weighed and measured.
After the trapping activities, it was time to continue multibeam sonar mapping activities. Prior to collecting the sonar data (and every 4 hours during data collection), mission scientists must perform a "CTD cast". This is simply a device that is lowered into the water to measure conductivity, depth, and water temperature from the surface to the bottom. Because the multibeam generates data using sound waves, it is critical to use the CTD data to calibrate the sonar, as these parameters can affect the velocity at which sound travels through the water. Below, Mission Chief Oceanographer Tim Battista can be seen along with Grant Froelich of NOAA's Marine Operations Center (MOC) discussing the next cast. Once the cast was completed, the sonar unit was turned on, and the Foster once again began to collect this valuable bathymetric and associated backscatter data. An example of a standard realtime output from the multibeam sonar unit is also shown below. This particular image shows a 10 meter rise of the seafloor, and likely represents a coral reef area that has never been mapped to date. NCCOS and its many partners will use these data to characterize and map the MSR all along the southern shore of St. John.
Be sure to check back tomorrow for the next set of maps and images from the Foster's mission in the US Virgin Islands!