Nursery Area Contribution to the Coast Wide Atlantic Menhaden Population

The Atlantic menhaden Brevoortia tyrannus is a clupeid that plays a critical role in the ecosystem and supports one of the largest fisheries in the Chesapeake Bay. Along with a decrease in overall numbers and spawning stock biomass, recruitment levels have remained low since the 1990s. Menhaden utilize numerous estuaries along the Atlantic coast for juvenile development before recruiting to the adult population and the contribution of each of these nursery grounds is unknown. To evaluate the resiliency of menhaden and identify areas that are essential for survivorship, the relationship between population structure and recruitment along the Atlantic coast needs to be fully assessed. The Chesapeake Bay is thought to contribute 70% of the total recruits, although that estimate is over twenty years old and predates current low recruitment levels. We investigated the potential of trace element (⁷Li, ²⁵Mg, ⁵⁵Mn, ⁸⁵Rb, ⁸⁸Sr and ¹³⁷Ba) and stable isotope (δ¹³C and δ¹⁸O) signatures in otoliths to distinguish between coast wide nursery grounds of the Atlantic menhaden for 2009-2011. We found that juvenile menhaden collected from Connecticut to South Carolina could be classified to their regional nursery grounds at nearly 90% accuracy. We found significant inter-annual variation in the elemental signatures so attempts to classify juveniles from other year-classes or using combined year-classes resulted in lower accuracy. However, this study provides a three-year library of elemental signatures for assigning adults to their region of origin. This research builds the foundation for a comprehensive estimate on recruitment rates from each of the major nursery areas along the US Atlantic coast for 2009-2011.