Award: OCE-0961632

Atlantic menhaden, hereafter menhaden, has been called the most important fish in the sea as it serves as a prey item for many ecologically and economically important marine mammals, birds and fishes, supports important commercial fisheries and provides key ecosystem services. Adult menhaden live in the coastal ocean, where they spawning principally during winter months. Young of year menhaden live in estuaries along the Atlantic seaboard, such as Chesapeake Bay. We do not understand factors that contribute to annual variation in the numbers of young menhaden. This project sought to determine how the location at which adults spawned in the ocean affected the spatial and temporal pattern of supply of young menhaden to coastal estuaries. We developed an individual-based physical-biological model that tracked menhaden from egg to juvenile as they grew and were dispersed by coastal currents. We used output from an operational physical oceanographic model (http://www.myroms.org/espresso/) and an existing particle tracking model (http://northweb.hpl.umces.edu/LTRANS.htm) to forecast movement of young menhaden. We assigned spawning to seven discrete locations in the ocean and tracked recruitment to seven distinct nursery areas (Figure 1) to evaluate the impacts of alternative hypotheses of adult distribution. Intellectual Merit: The project greatly advanced our understanding of how processes during the coastal phase impact menhaden abundances. Results indicated why particular estuaries are key nursery areas for menhaden and the extent to which these key areas may shift as (i) older fish become more common in the population and/or (ii) the coastal ocean warms leading to a northward shift of spawning. We showed that recruitment of menhaden occurred downstream, generally south of spawning locations, with the exception of Long Island. We also demonstrated mechanisms underlying the episodic nature of menhaden recruitment. We identified the importance of dispersal in forecasts of when and where young menhaden recruit to estuaries. Within this framework we explored physical processes including horizontal diffusivity and biological, behavioral processes and found that physical processes dominate. We also developed a new information theory based approach to understanding the evolutionary advantages of multiple spawning locations and nursery sites. Using a network model we quantified whether specific spawning locations reliably (% of months and years) or efficiently (% of total recruits) contributed recruits to specific nursery areas. Some spawning locations were characteristically efficient; others more reliable. But importantly, site-specific efficiency and reliability estimates were highly variable among years, such that identification a priori of an optimal spawning strategy was not possible. Broader Impacts: Project results have been used to inform management approaches to menhaden. The projected directly generated 2 manuscripts that have been submitted for publication, 1 will be submitted shortly and 2 additional manuscripts based on our collaboration with Dr. Cynthia Jones (ODU). The project also resulted in 4 presentations and 1 invited presentations at national and international meetings. Moreover, the project resulted in the advanced training of one post-doctoral fellow, Erdem Karakoylu who is now employed as a senior application engineer by NASAÆs Science and Exploration Directorate in Greenbelt, MD Last Modified: 03/09/2015 Submitted by: Thomas J Miller