Award: OCE-0961421

The Atlantic menhaden, Brevoortia tyrannus, plays a critical role in the marine food web as an important prey item in the diet of many important food fish and supports on of the largest fisheries on the east coast. Along with a decrease in overall numbers and biomass of reproductively-capable adults, recruitment of young to the adult population has remained low since the 1990s. Thus, it is necessary to evaluate the impediments to juvenile survival and recruitment if we are to establish proper management for this prey species.

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 thought to contribute 70% of the total recruits, although this estimate is over twenty years old and predates current low recruitment levels. We used the chemistry in otoliths (earbones) to distinguish between coast-wide nursery grounds of menhaden for 2009-2011. We determined that juvenile mehaden could be classified to their regional nursery grounds accurately and that otolith chemistry provided a natural tag to follow the contribution of each nursery area in subsequent years. This research builds the foundation for a comprehensive estimate on recruiting rates for each of the major nursery areas along the US Atlantic coast for 2009-2011. Analysis of age-1 signatures revealed that the Chesapeake Bay and the Northeast nursery grounds each consistently contributed ~30% of the new recruits over the three years of this study, followed by the Southeast and Delaware Bay with ~20%. Analysis of age-2 and age-3 will show which nursery has the highest survivorship based on classification of the older age classes.

Concomitant with the application of otolith chemistry, our collaborators at CBL and Rutgers University have developed a circulation model that was parameterized with our data and revealed the necessay circulation and timing that provided young fish to the nursery areas from menhaden's offshore spawning grounds. Moreover, the model is also able to show that changes in circulation can alter the delivery of young and, this, affect potential recruitment under climate change impacts.

The project has supported two Post-doctoral Fellows, one a Native American, and one Ph.D. student who has used the project as the foundation for her dissertation. Several papers have been published, with several more in progress. The Post-doctoral Fellows and Ph.D. student have been actively presenting the results of this research in international and national forums. We have made the results of the project available to the Atlantic States Marine Fisheries Commission and they have asked us to participate in a menhaden ageing workshop which is using our age samples as a reference set.

Last Modified: 09/05/2014
Modified by: Cynthia M Jones