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December 2007 E-Update
By Jim Hawhee, APNEP Staff
APNEP scientist Dr. Dean Carpenter and Dr. Jud Kenworthy, co-chair of APNEP's Science and Technical Advisory Committee,
Enjoying the spoils of an unseasonably warm October, APNEP and a broad coalition of partners have again successfully acquired the information necessary to map aquatic grasses in our region’s coastal waters.
These grass beds, known to scientists and managers as submerged aquatic vegetation, or SAV, are a valuable aquatic habitat. In addition to producing dissolved oxygen, these grasses filter pollution and provide food and shelter for fish, shellfish and crustacean species. They are also important to resident and migratory waterfowl.
Dense aquatic grasses in Currituck Sound
This year, mapping efforts focused on the northern waters of the Albemarle-Pamlico region, from Roanoke Island to Virginia’s Back Bay. It is no exaggeration to suggest that aquatic grasses are intimately intertwined with the area’s rich cultural heritage.
Nutritious wild celery and a host of other grass species draw migratory waterfowl to this area of the Atlantic flyway. For hundreds of years, hunters have followed. Historically, hunting clubs like Corolla’s Whalehead Club dotted the region. Back Bay National Wildlife Refuge occupies the site of two former hunt clubs, the Princess Anne and Ragged Island Hunting Clubs. To this day, duck blinds litter the waters of the Currituck coastline.
A duck blind near the Currituck mainland, crabbers ply the sounds as the sun rises
More than just birds thrive in this habitat, however. APNEP’s field team tipped their caps to professional watermen pulling pots from the water as the sun emerged over the horizon. Hundreds of buoys marked the location of individual crab pots, and field teams made several detours around pound nets set to capture fish in the area.
Despite its tremendous importance, mapping aquatic grasses is among the most technically and logistically challenging endeavors our coastal managers face.
No single federal or state agency in North Carolina or southeastern Virginia has an explicit mandate to monitor the location, extent or changes in these grasses. As a result, funding for these efforts is not available from any one source. Yet because several agencies and organizations rely on this information to evaluate permit applications, assess water quality and gauge the extent of our estuarine habitats, many were able to lend support to this collaborative effort.
Dr. Maurice Crawford of Elizabeth City State University identifies grass species, Brad Fitzgerald of the N.C. Division of Marine Fisheries measures water clarity using a secchi disk.
Led by APNEP’s Dr. Dean Carpenter, participating partners included the N.C. Department of Transportation (NCDOT), N.C. Division of Marine Fisheries, Back Bay National Wildlife Refuge, Virginia’s False Cape State Park, Virginia Department of Game and Inland Fisheries, Elizabeth City State University, the North Carolina Coastal Federation, NOAA’s Beaufort Lab and Monitor National Marine Sanctuary, Jennette’s Pier, Outer Banks Cruises, Town of Duck, and the Outer Banks Center for Dolphin Research. Many of these agencies and organizations also participate in the SAV Partnership, a working group formed by APNEP to research, monitor and improve this important resource.
In 2009, APNEP received a grant from the N.C. Coastal Recreation Fishing License program to recommend protocols for the long-term monitoring of SAV in North Carolina. Due to differing conditions throughout the sounds and coastline, data is collected by a combination of aerial imagery, boat-based acoustic techniques, and underwater cameras. In addition to optimizing the extent of grasses that can be detected, the use of multiple techniques offers a more cost-efficient means to collect the information.
Wild celery, Vallisneria americana, is a dominant species in estuarine areas with low salinity.
This October mapping effort marks the first implementation of the protocol. In 2013, new flights will collect imagery along the Outer Banks from Manteo to the White Oak River.
Far from simply taking snapshots, the collection of SAV imagery is an orchestrated symphony. Volunteers throughout the coastal area took periodic water clarity samples and reported back to APNEP. This information and detailed weather forecasts are used to identify often elusive flight windows. During most days, suspended sediment, high prevailing winds, excessive humidity, or even the angle of the sun make it difficult to detect SAV from the air.
Once the decision is made to launch, flights are completed in just a few hours. Pilots from the N.C. Department of Transportation’s Photogrammetry Unit fly a Beechcraft C-90 plane over the sounds at 10,000 feet. Housed in the bottom of the plane is a sophisticated multispectral camera that snaps high-resolution digital images at regular intervals. Through a technically demanding and time-intensive process, the images are then converted into maps of dense and patchy SAV beds.
A Beechcraft C-90 (left) houses the multispectral camera used to detect SAV (photos courtesy of NCDOT Photogrammetry Unit).
To ensure the accuracy of the maps, several field teams also sampled the grasses by boat. The presence, absence and density of grasses can be compared to the imagery to ensure the map reflects conditions in the water. The teams visited nearly 300 stations, most within a week of the flight. Salinity, water clarity, temperature, grass density and species were among the metrics recorded.
In addition to being a valuable aquatic habitat, aquatic grasses are sensitive to pollution. As such, changes in the extent of grass beds show whether efforts to improve the sounds are working.
In late 2011, APNEP released the first map of submerged aquatic vegetation for the Albemarle-Pamlico region and the North Carolina coast. With this effort, comparable data from Currituck Sound and Back Bay are available for 2007 and 2012. For the first time, managers will be able to map and measure changes in the extent of these grasses on a broad scale. No matter the outcome, this result is an important step forward for the stewardship of our sounds.