ACOUSTIC BOTTOM CLASSIFICATION OF OYSTER HABITAT IN THE MULLICA RIVER ESTUARY

Acoustic methods allow seafloor sediment types to be mapped at higher spatial density and more quickly than manual methods. These technologies can be used as well for mapping new oyster bed habitats and monitoring the spatial extent of known oyster beds. The Mullica River in southern New Jersey contains one of the last known self-sustaining wild oyster populations in the Mid-Atlantic. With increasing sea levels, oyster habitat may move further landward in the river. Preservation of this vital resource will be helped by the ability to rapidly assess bottom types and locate new reefs. The goal of this study was to develop a bathymetry map and acoustic bottom classification of a section of the Mullica River estuary. We used an Edgetech 6205 dual-frequency multibeam and sidescan sonar system in conjunction with Hypack surveying and data processing software to map a 37.2 hectare region of the study area. Grab samples of bottom sediment were described in the field and subject to sieve and pipette analysis to ground-truth the acoustic results. The acoustic bottom classification found large areas of the bottom to be predominantly clay. Other part so the channel had very patchy sediments ranging from clayey sand to gravel. Known oyster beds were not identified by the acoustic response analysis. Grab sample sediment types were consistent with the range of sediment types determined by the acoustic analysis, but included oysters. The correspondence between grabs and acoustic analysis will also be discussed.