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Virginia Sea Grant funded research

Characterization of the sub-population contribution of age-0 Atlantic menhaden to
Chesapeake Bay

Jason Schaffler, Cynthia Jones (Old Dominion University)

Our goal for this project is to address the metapopulation structure and localized depletion of menhaden in Chesapeake Bay. We will do this through the use of otolith chemistry by comparing chemical signatures from known source locations to chemical signatures from menhaden leaving the Bay to take part in the coastal migration. In 2007, we will develop nursery-area specific otolith chemical signatures from young-of-the-year menhaden using both trace element analysis and stable isotope analysis. In 2008 we will determine the proportion of recruits originating from each nursery area in the out-migrating population of juvenile menhaden, and address the potential for yearly variability in the nursery specific otolith chemical signature of juvenile menhaden.

Both trace element analysis and stable isotope analysis are effective methods of separating populations of fish.  Until recently, these techniques had never been combined.  Together, they represent one of the most powerful methods of population discrimination.  We will measure a suite of trace elements along with δ13C and δ15N in the otoliths of juvenile menhaden collected from five nursery areas in Chesapeake Bay to determine nursery specific chemical signatures.  This information will be compared to chemical signatures from juvenile menhaden collected out-migrating from the bay in fall using a maximum likelihood analysis procedure.

The work proposed here is an important step in evaluating the menhaden fishery in Virginia’s coastal waters as well as along the Atlantic coast.  Chesapeake Bay is believed to contribute up to 70% of the total number of recruits to the menhaden fishery.  Regardless of the true fraction of the coastal population of menhaden Chesapeake Bay produces, it is the dominant Atlantic menhaden nursery.  It is imperative that we understand where these recruits are produced within the Bay and this work is that first step that will allow us to determine which rivers are serving as the dominant nursery areas.