Wind and tidal influences on larval crab recruitment to an Oregon estuary

We investigated wind and tidal forcings that may facilitate transport of crab megalopae to a northeast Pacific coastal estuary. Daily abundance of crab megalopae was estimated from light trap collections made from March 1998 through December 2001 in Coos Bay, Oregon, USA. The Dungeness crab Cancer magister dominated the catch; Cancer Group I (C. productus and C. oregonensis), Hemigrapsus oregonensis and Pachygrapsus crassipes megalopae were also abundant enough for statistical evaluation. The abundance time series data were analyzed in relation to mean daily wind stress, maximum daily tidal range, and mean daily temperature residuals using cross-correlation and cross-Fourier techniques. Variation in wind stress had little relation to variation in crab megalopae abundance. Rather, crab megalopae were found to recruit to the estuary at periods close to the spring-neap tidal frequencies. Increased catches were not coincident with spring tides; most tests indicated that ingress occurred at times ranging from several days after spring tide to near the neap tide, but this varied among species and years. Tidal forcing appears to control crab recruitment to this estuarine system.