|
||||||
|
|
|||||||
|
||||||||
|
Paleoshorelines and Spawning Groupers—Deep Diving at the Shelf Edge, Northeastern Gulf of Mexico
From March 21 to 28, 2005, Kathy Scanlon and Julia Knisel of the U.S. Geological Survey (USGS) Woods Hole Science Center were in the northeastern Gulf of Mexico collecting rocks near the West Florida shelf edge. The work was conducted from the National Aeronautics and Space Administration (NASA)'s 176-ft retrieval ship Liberty Star, one of two ships built to recover the Space Shuttle's solid rocket boosters and return them to Kennedy Space Center for refurbishment. Owned by NASA and operated by the United Space Alliance, the ships also support other missions, such as scientific investigations. Collecting rocks at water depths of 75 m (nearly 250 ft) was not a trivial task—it required a remotely operated vehicle (ROV) equipped with video cameras, and a team of four divers qualified to do deep technical diving, breathing specially mixed gases instead of ordinary air. The divers could stay on the bottom for about 15 minutes and needed to spend 1 to 1.5 hours at shallower depths for decompression. Rock outcrops were first located using the ROV, and then the divers followed the ROV cable to the bottom and set to work quickly with chisels and sledges to collect fresh rock samples. The cruise was part of a collaborative effort between USGS geologist Kathy Scanlon (Woods Hole, MA) and Florida State University (FSU) biologists Felicia Coleman and Chris Koenig (Tallahassee, FL). Coleman and Koenig are studying the effects of fishery-closed areas on spawning grouper populations. The ROV was used to assess the numbers and sizes of gag, scamp, red grouper, and other fish at numerous sites both inside and outside the protected areas, and to observe spawning behavior. Many of these fish spawn at rocky shelf-edge outcrops that are believed to have been formed along paleoshorelines during the Pleistocene, when sea level was considerably lower. Analyses of the rocks collected on this cruise will help determine their age and environment of formation, knowledge that may lead to refinement of paleo-sea-level curves. It will also allow us to model where similar paleoenvironments may occur, information that is very useful for fishery management. In addition, compositional analysis may help shed light on the mystery of why groupers spawn at some outcrops but not at others. Funding for this work came from the National Oceanic and Atmospheric Administration (NOAA)'s National Undersea Research Program (NURP) through the National Undersea Research Center at the University of North Carolina, Wilmington (NURC/UNCW), which paid for the ship time and provided the technical divers, the ROV, and the ROV operators.
|
 |
in this issue:
Scientist Shares USGS Work Experience with Students USGS Oceanographer Interviewed About Erosion by Hurricanes
Employee Recognized for Providing Maps to Police Mendenhall Fellows Join Western Coastal and Marine Geology Team Operations Assistant Joins Western Coastal and Marine Geology Team
 |
||||||||||||||||||||||||||||
U. S. Department of the Interior | U.S. Geological Survey
cover story:
