Blue crab (Callinectes sapidus) larval settlement in North Carolina: environmental forcing, recruit-stock relationships, and numerical modeling

Ecosystem‐based fishery management requires an understanding of relationships between fisheries and environmental variability. The purposes of this study were to investigate (1) how environmental forcing drives variability in larval settlement of the blue crab Callinectes sapidus, (2) whether larval settlement data are useful for determining recruit–stock relationships, and (3) whether environmental data can be used to predict settlement. Megalopae settling on passive collectors in the Newport River estuary, NC, were collected nightly from September to November for 13 yr from 1993 to 2009. Observed settlement was compared with winds, tides, and predicted settlement (numerical model derived from environmental data) using cross‐correlation analysis. Weather events associated with settlement pulses were also identified. Recruit–stock relationships were developed by comparing observed and predicted settlement indices to lagged NC fishery data. Settlement was positively correlated with winds from the northeast, southeast and south in 12 of 13 yr and with maximum duration nighttime flood tides in all years. Settlement pulses occurred when high pressure systems formed over the southeast USA (58% of pulses) or hurricanes (25%), and nearly all occurred during nighttime flood tides (85%). Significant recruit–stock relationships occurred between observed settlement and fishery landings (r2 = 0.96) and effort (r2 = 0.94) in wet years and catch per unit effort (r2 = 0.98) during dry years. The timing of settlement pulses, but not the magnitude of annual settlement, was successfully predicted using the settlement model. These results suggest that blue crab fisheries in NC are influenced both by larval settlement and post‐settlement processes (freshwater inflow).