Spatiotemporal Dynamics of Atlantic Menhaden Recruitment in the Northwest Atlantic Ocean

Atlantic menhaden is an abundant, clupeid forage fish that supports the largest single-species fishery in the eastern USA.  Its stock-recruitment relationship is poorly defined and relatively little is known about factors that regulate recruitment.  To better understand Atlantic menhaden spatiotemporal recruitment dynamics, we analyzed fishery-independent recruitment time-series (1959-2012) along the eastern USA using dynamic factor analysis.  We explicitly tested for effects of climatic, environmental, ecological, and anthropogenic variables that were documented or hypothesized to have correlative or mechanistic influence on stock productivity.  Annual recruitment time series grouped geographically and were characterized by two different periods of high recruitment.  Chesapeake Bay indices were high from ~1970-1992 whereas New England indices were high from ~1995-2005.  Examined covariates did not explain the time periods of greater productivity, which suggests complex interactions among variables, nonlinear covariate effects including regime shifts or threshold responses, or the influence of alternative process scales or variables.  The regionally distinct recruitment dynamics could be due to variation in spawning locations or a level of spatial stock structure.  These regional patterns have implications for the stock assessment of Atlantic menhaden, particularly given the geographically constrained nature of the fishery to Chesapeake Bay and the neighboring coastal ocean.