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

Abstract

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 (r 2 = 0.96) and effort (r 2 = 0.94) in wet years and catch per unit effort (r 2 = 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).

The Distribution of Blue Crab (Callinectes sapidus) Megalopae at the Mouths of Chesapeake and Delaware Bays: Implications for Larval Ingress

“…This result is consistent with inferred recruitment mechanisms for C. sapidus in the Mississippi Bight (Perry et al 1995(Perry et al , 2003 and in North Carolina estuaries (Ogburn et al , 2012Eggleston et al 2010). In Mississippi sound, settlement of C. sapidus megalopae has been correlated with onshore wind-forcing events as well as spring tide events (Perry et al 1995).…”

“…In addition, wind forcing has been identified as an important factor for returning C. sapidus megalopae to near-shore habitats in the Mississippi Bight (Perry et al 2003). In contrast, flood tide transport may be more important for C. sapidus megalopae, or at least easier to detect, when they recruit through narrow inlets like those in North Carolina (Forward et al 2004;Ogburn et al , 2012Eggleston et al 2010). It is not unreasonable to expect that differences in behaviors and relative importance of ingress mechanisms would exist between estuaries with large mouths like Chesapeake and Delaware Bays (~35 km) compared to inlets where tidal currents are accelerated in the narrow mouths (~1 km) and salinity signals change rapidly over several kilometers instead of over tens of kilometers.…”

“…The combination of these environmental cues could result in increased vertical swimming during nocturnal flood tides (NFTs), which may result in transport up-estuary during NFTs. Once within estuaries, nocturnal flood tide transport (NFTT) is believed to be the dominant mode of up-estuary transport of C. sapidus megalopae (Tankersley and Forward 2007), which is supported by the fact that settlement patterns of megalopae within Pamlico estuary are significantly correlated with the duration of NFTs (Ogburn et al , 2012Eggleston et al 2010). If tidal changes in salinity and turbulence occur beyond estuary mouths, C. sapidus megalopa vertical distribution, and hence transport, may be influenced.…”

“…These winddriven events are a likely mode of C. sapidus megalopa ingress to estuaries in the Middle Atlantic Bight (Goodrich et al 1989;Little and Epifanio 1991;Jones and Epifanio 1995;Olmi 1995;Roman and Boicourt 1999;Epifanio and Garvine 2001;Tilburg et al 2005;Epifanio and Tilburg 2008;) and could result in year-to-year variation in blue crab recruitment (Sulkin and Epifanio 1986;Ogburn et al 2012).…”

Evaluation of Blue Crab, Callinectes sapidus, Megalopal Settlement and Condition during the Deepwater Horizon Oil Spill

“…sapidus megalopal settlement into estuaries is known to be extremely variable both among sites and within the same sites over time [ 11 , 12 ], but there is little consensus on the causes of this variation. Previous studies have attributed some of this variability to seasonal, lunar, meteorological, or hydrological drivers as outlined in Table 1 [ 11 – 25 ], but have collectively failed to identify consistent drivers across sites or years [ 26 ]. Given that the independent variables and statistical methods varied among these studies, the effects of different drivers on C .…”