Natal Origin of Central Southern Management Area, North Carolina Striped Bass, Inferred from Otolith Microchemistry

Abstract

Striped bass (Morone saxatilis) is an important commercial and game fish throughout North Carolina coastal waters. These fish have spawning populations present in all of the state's coastal rivers, however populations south of the Albemarle Sound in North Carolina have rarely been studied. These populations lie within North Carolina's immense Central Southern Management Area (CSMA). The CSMA stretches from the northernmost point of Pamlico Sound in the north down to the South Carolina border in the south. There are three main watersheds in the CSMA: the Tar/Pamlico River, the Neuse River, and the Cape Fear River. These rivers have spawning populations of striped bass, yet very few age 0 fish have been collected to support this in recent years. My study investigated the natal origin of CSMA striped bass through the use of water and otolith elemental analyses. Surface water samples and environmental data were collected once per month from 15 sample sites throughout the CSMA from May 2011 to July 2012. Two additional sample ponds from Edenton National Fish Hatchery were sampled once per week for two weeks in April 2012. Samples were analyzed for concentrations of calcium (Ca), strontium (Sr), magnesium (Mg), barium (Ba), and manganese (Mn) using an inductively-coupled plasma optical emission spectrometer. Concentrations were recorded as element to Ca ratios to account for the role of Ca in otolith deposition. Salinity differed significantly by location, while temperature and dissolved oxygen differed significantly by month and season. Only temperature differed significantly by year. All measured elements were consistently detected at every sample site. All measured elements differed significantly by location, but only Mn differd by month, season, and year. A multivariate classification of samples to their river of origin yielded only 42% success. When the classification was narrowed to include only one low salinity sample site per river, samples were classified to their sample site of origin with 82% accuracy. Fish (N=251) were collected from the Neuse and Tar/Pamlico rivers from April 2011 to April 2012. Fish total length (TL), total weight (TW), gonad weight, and liver weight were collected to calculate relative weight (Wr), liver somatic index (LSI), and gonadal somatic index (GSI). Otoliths were removed for ageing and elemental analysis. Elemental analysis was conducted by measuring concentrations of Sr, Mg, Mn, and Ba in the natal origin region of the otolith using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Condition of fish collected in the Neuse and Tar/Pamlico was sub-optimal. Fish GSI follow predictable yearly cycles, but were maturing a full year earlier than Roanoke River striped bass. Using the Sr signature from otolith elemental analysis, 88.4% of fish originated from the hatchery. Fish determined to be of natural origin were classified to their river of origin with 58.0% accuracy, and to their management area of origin with 84.0% accuracy. This study suggests that striped bass has become a put and take fishery in the Neuse and Tar/Pamlico rivers.