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2010 Deep Sea Coral Cruise - east coast
Mission info 2007 Nancy Foster Cruise
 

Mission Summary

By George Sedberry
Gray's Reef National Marine Sanctuary

Although the cruise aboard the Pisces was short and conditions were not ideal, we accomplished several important tasks.  The Pisces, commissioned in November 2009,  is one of NOAA’s newest ships, and is still undergoing sea trials.  This cruise gave the ship, crew and scientists the opportunity to test the ships systems, including its sophisticated automatic data logging and sonar systems, under a variety of rigorous conditions at sea.  We were able to deploy an ROV, bottom grab, plankton net, and CTD to sample the water and the bottom, and we were able to use the ship’s acoustic Doppler current profiler (ADCP) to measure currents and the fisheries acoustic system to map the bottom and fish aggregations.

The cruise was aimed at observing and sampling deep coral banks in 400-500 m of water off the coast of Georgia. Unfortunately, the Gulf Stream flow was particularly strong at all of the intended sampling sites. Although we tried three areas in different depths and distances from the center of the main current, we could not find conditions that would allow us to lower the ROV to the bottom and still maintain the ship's position above.

A sea-surface temperature image, measured by satellite, shows a very strong deflection of the Gulf Stream off northern Georgia, with large meanders and eddies downstream.  The strong deflection is thought to be related to volume transport by the Gulf Stream, and a particularly strong Gulf Steam current (greater than 4 knots) was detected at our intended dive sites near latitude 31°30'N.  Moving north of 32°N got us out of the Gulf Stream so we sampled known hard bottom and coral habitat at depths around 200 m (600ft) near 32°40’N off Georgetown, SC.
A sea-surface temperature image, measured by satellite, shows a very strong deflection of the Gulf Stream off northern Georgia, with large meanders and eddies downstream. The strong deflection is thought to be related to volume transport by the Gulf Stream, and a particularly strong Gulf Steam current (greater than 4 knots) was detected at our intended dive sites near latitude 31°30'N. Moving north of 32°N got us out of the Gulf Stream so we sampled known hard bottom and coral habitat at depths around 200 m (600ft) near 32°40'N off Georgetown, SC. Click here or on the image for a larger version.

Most ROV dives were conducted at a site known as “Georgetown Holelink leaves the sie, a popular fishing spot and documented spawning ground for snowy grouperlink leaves the sie. This site was chosen because it is north of the area where the Gulf Stream turns east, thus getting us out of the current and into an area where deep corals are known to occur.  The depth ranged from 150 – 250 m, so the species of corals were different from what we had planned to sample.  The area has been previously exploredlink leaves the sie and the hard bottom there is particularly complex because of ancient iceberg scourslink leaves the sie on the bottom. 

The image depicts bottom topography as measured with multibeam sonar surveys conducted in the study area called Georgetown Hole, off South Carolina.  The channels on the image were carved by icebergs during the last glaciations.  The gouges in the bottom are 10 to 100 m wide, more than 10 m deep and exceed 10 km in length. The shallowest of them end at 120 m depth, and they extend out to about the 220-m depth line.
The image depicts bottom topography as measured with multibeam sonar surveys conducted in the study area called Georgetown Hole, off South Carolina. The channels on the image were carved by icebergs during the last glaciations. The gouges in the bottom are 10 to 100 m wide, more than 10 m deep and exceed 10 km in length. The shallowest of them end at 120 m depth, and they extend out to about the 220-m depth line.

The edges of the iceberg scours were characterized by craggy rock features and overhangs populated by blackbelly rosefish and snowy grouper. Small primnoid sea fans and barrel sponges were abundant, as were small sponges, white anemones, tubeworms, bristleworms, pencil urchins, and hydroids.

In addition to obtaining samples and images, we surveyed each site with the Simrad EK-60 split-beam fisheries acoustics system aboard the PISCES. We conducted over 24 hours of split-beam fisheries surveys, along with bottom mapping, primarily at dawn and dusk over a variety of habitats to map fish abundance in the water column. These surveys also guided the selection of ROV dives as we were able to pick out bottom features such as coral mounds and glacial scours to study further. The acoustic survey transects were conducted at the same locations as the ROV sites, giving us a method of groundtruthing the acoustic targets and providing a broader scale view of the ROV dive sites. Having surveyed areas known to support wreckfish, snowy grouper, and yellowfin bass, we expected to see relatively large numbers of fish in the water column. Rather than seeing large numbers of individual fish or fish schools, we primarily saw evidence of the scattering layer produced by abundant masses of zooplankton. Select areas, where bottom features were evident, contained both small and large schools of fish. The results from the fisheries surveys will be used to map the distribution of biomass in the water column, as well as the size distribution of targets. These maps will describe where, when and how biota are assembled in the water column. The echograms shown here indicate fish biomass associated with bottom features. Fish schools exhibit dense schooling behavior at certain times and a more dispersed distribution at other times. This leads to interesting questions as to how this arrangement affects the ecology of these places in terms of predator-prey interactions, schooling as a defensive mechanism, diel feeding patterns, and association of fish with particular features and locations.

A screen grab from the fisheries acoustic system aboard the PISCES.  This is from the 38 kHz transducer and shows the bottom profile (red) consisting of coral mound and rough bottom on a rising ledge system.  Fish schools are seen “stacked up” near the rough bottom on the left side of the bottom profile, and smaller organisms (zooplankton) are seen in a “cloud” above the bottom.
A screen grab from the fisheries acoustic system aboard the PISCES. This is from the 38 kHz transducer and shows the bottom profile (red) consisting of coral mound and rough bottom on a rising ledge system. Fish schools are seen "stacked up" near the rough bottom on the left side of the bottom profile, and smaller organisms (zooplankton) are seen in a "cloud" above the bottom. Click here or on the image for a larger version.

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