Date of Award

Winter 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

Cynthia M. Jones

Committee Member

Alexander Bochdansky

Committee Member

Norou Diawara

Abstract

Understanding the population structure and patterns of connectivity in marine fishes is essential when making predictions about a species' resiliency and persistence in an increasingly changing environment. The Atlantic Menhaden Brevoortia tyrannus is a clupeid that plays a critical role in the marine food web and supports one of the largest fisheries on the US East Coast. In addition to a decrease in overall numbers and spawning stock biomass, recruitment levels have remained low since the 1990s. Menhaden use 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 currently unknown. The Chesapeake Bay is believed to contribute 69% of the total recruits, although this estimate has never been quantitatively verified and is 25 years old, predating current low recruitment levels and increased development along the coastline. This study investigated the potential of trace element (Li, Mg, Mn, Rb, Sr, Y, Ba and Pb) and stable isotope (δ 13C and δ18O) signatures in otoliths to distinguish between coast-wide nursery grounds of menhaden for 2009-2011. Using geochemical signatures specific to each year, juvenile menhaden collected from Connecticut to South Carolina were classified to regional nursery grounds at nearly 90% accuracy. The geochemical signatures were applied to adult menhaden of unknown natal origin that corresponded to these year-classes to determine which nursery is producing the most recruits to the fishable stock. The results indicate that while the Chesapeake Bay still dominates the proportion of age-1 recruits, the Bay's contribution has declined by 16-65% of the earlier estimate. Additionally, an evaluation of older age classes (ages 2-4), the spawning stock, offered a more complete assessment with nearly 70% of adults originating from the Northeast and Southeast nursery grounds rather than the Mid-Atlantic as previously believed. This study successfully evaluates historical estimates of nursery contribution for menhaden, identifies regions that are currently essential for survivorship of this population, and, thus, provides critical information to future stock assessments for this species.

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DOI

10.25777/251w-zf83

ISBN

9781321558647

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