Savannah, Georgia – Beginning in 1970, the Georgia Department of Natural Resources constructed a series of man-made reefs to provide habitat for marine life. However, until recently there were gaps in some of the key information about these reefs, such as the precise locations of material placed on the bottom and the water depth on the material. Today, researchers at the University of Georgia’s Skidaway Institute of Oceanography are using side-scan bathymetric sonar and high-resolution geographic positioning systems (GPS) to provide coastal managers and fishermen with a detailed image of the location and condition of reef material.
The Georgia Shelf is relatively shallow, stretching about 80 miles offshore before plunging into the deep ocean. Most of the shelf bottom is quicksand, which does not provide the kind of conditions to develop and support various reef communities.
“Much of the continental shelf looks like a vast desert of sand,” said Clark Alexander, a scientist at the UGA Skidaway Institute. “So what we need is a harder substrate, because that is really the most important thing in establishing stable communities that are alive and well. “
Over the past 50 years, the state has placed hard surface materials at 18 sites, each covering an area of approximately 15 square kilometers. Eight of the sites are located along the coast about 10 miles offshore and eight others are about 25 miles offshore. There are also two ‘beach reefs’ which are closer to shore and accessible to fishermen with smaller boats. The reefs are made up of a wide variety of materials, including old ships, battle tanks, parts of the original Talmadge Bridge, retired New York subway cars, concrete pipes and pilings, and Specially designed concrete tetrapods.
“The materials that were placed on the bottom in the 1970s and 1980s were either sunk in place or deployed from barges using Loran-C, a radio navigation system that was significantly less accurate than current GPS, or dropped from the sea. ‘army helicopters, so their precise locations are not always exactly known, “Alexander said. “Additionally, we’ve had a number of hurricanes and winter storms that have passed through or off Georgia, and we don’t know if any of the material has been moved from its original location.”
Alexander proposed a program to study reefs and develop a more precise dataset of their locations and characteristics, which was later funded by the Georgia Coastal Management Program, administered by the Georgia Department of Natural Resources Coastal Resources Division.
“Our goals were to document the state of what lies at the bottom and give more precise locations for the objects that we identify,” Alexander said. “We used real-time kinematic GPS so we know down to a few inches where things are down there. “
Alexander’s team began fieldwork in 2018 and continued into 2021, using the 28ft Jack Blanton RV. They spent an average of six days studying each reef. They started with the beach reefs to solve the problems with the planned survey approach, then moved on to the reefs 10 miles offshore. In addition to high-resolution GPS, the team used side-scan interferometric sonar that provides depth and co-recorded side-scan sonar images that provide images of the seabed and objects within it.
“Based on the general location of an object and the existing location data, we were able to make some good guesses as to ‘Oh, that must be a certain barge or a certain ship” and so on. ” he declared. “And we found a few items that weren’t on existing maps and several more that had fragmented into several pieces since they were placed.”
Another important parameter the team measured was the amount of clearance between the different structures and the ocean surface.
“You don’t want to have to worry about anything that you consider to be a boating hazard,” Alexander said. “Ten miles offshore you’re in about 10 yards of water, about 30 feet. So if any of these sunken ships were to rise a significant height above the bottom, this is something you need to know. “
Alexander and the DNR plan to survey the eight reefs about 25 miles offshore. They present a greater challenge than reefs closer to shore. Longer distance means longer transit time and less time on station to survey. The team would also be constrained by the weather. Conditions should be very good and the forecast should remain calm throughout the transits and the survey.
“Because when you are this far offshore you are at the mercy of sea conditions, which can change quickly,” said Alexander.
Data collected by the Alexander team is now being added to the DNR Marine Artificial Reef Fishing website. These new data products improve the data available to anglers and now allow users to zoom in on individual characteristics, see what they look like and how they are distributed relative to other characteristics of the bottom. The data collected by the project can be viewed on the DNR site on artificial reefs: https://coastalgadnr.org/HERU/offshore