Using Water Chemistry and Otolith Chemistry to Determine Strategic Habitat Areas for Striped Bass (Morone saxatilis) in the Albemarle Estuarine System of North Carolina

Abstract

Striped bass (Morone saxatilis) is an important anadromous species that provides valuable ecological and economic benefits to North Carolina. Habitat degradation, alteration and destruction are ongoing, and agencies are lacking the information needed to determine what habitat areas need protection. The North Carolina Coastal Habitat Protection Plan (NC CHPP) recommends that Strategic Habitat Areas (SHAs) be identified in order to maintain water quality and protect the ecosystem that serves our fisheries. Trace elements found in the water chemistry can be compared to elements deposited in the otolith. Otoliths, or ear bones in fish are calcified structures that incorporate elements from ambient water that is encountered by the fish. Fish residing in the AES can have a multi-elemental signature in their otoliths that can be a reflection of the water chemistry of the rivers. The temporal and spatial stability of the water chemistry must be determined before otolith chemistry can be used to establish nursery habitat. The temporal and spatial stability of water chemistry in each watershed of the AES was examined over multiple sampling sites and seasons. Sr:Ca, Ba:Ca, Mn:Ca, and Mg:Ca ratios differed significantly spatially, but not temporally (with the exception of Mg:Ca) and multi-element signatures correctly identified habitats with between 79-89% accuracy. Once the spatial and temporal stability of the water chemistry was evaluated, otoliths of adult striped bass were analyzed to determine SHAs used in their first summer of life. Adult striped bass were collected from Albemarle Sound and Roanoke River during the pre-spawn through post-spawn period from March-May of 2009 and 2010. Concentrations of strontium (Sr), barium (Ba), manganese (Mn), and magnesium (Mg) at the 60-120 day post-hatch period in adult otoliths were measured to determine habitat specific signatures and to establish the relative contribution of fish from each nursery habitat. Random Forests (JMP Pro 11.2) analysis was applied to otolith chemistry to successfully assign adult fish to one of four watershed containing nursery habitat. Model testing was completed by analyzing the juvenile (60-120 days post-hatch) portions of the adult otoliths from the 1994 to 2006 year classes (Age 3 to Age 16; n = 206). Results indicate the highest portion (60.87% to 76.47%) of adult striped bass sampled in my study were predicted to have used the Perquimans River as their nursery habitat area and subsequently survived to spawn as adults. Only a small portion of the Perquimans River is currently designated. My study results indicate that the Perquimans River appears to be important striped bass nursery habitat and therefore needs additional protection. Management implications resulting from changes in current SHA designations are discussed, not only for striped bass sustainability via the NC CHPP but also for the furtherance of existing additional environmental management programs or initiatives (e.g., the Albemarle Pamlico National Estuary Partnership's Comprehensive Conservation and Management Plan [CCMP], and the South Atlantic Landscape Conservation Cooperative's Conservation Blueprint 2.0).