TIDAL STREAM TRANSPORT OF WEAKFISH LARVAE IN DELAWARE BAY, USA

We conducted discrete-depth, hourly sampling for larval weakfish Cynos cion regalis at a station in southern Delaware Bay, USA, during the sp awning seasons of 1988 (131 h) and 1989 (150 h). During both years, co incident measurements of current velocity, salinity, and temperature w ere made at 2 depths in the water column and tidal-height data were ob tained from a nearby NOAA tide gauge. Results of nonparametric analysi s of variance showed that larvae were significantly more abundant at d epth than at the surface. Post-yolksac larvae were significantly more abundant during flood tides, but there was no effect of tidal stage on the abundance of yolksac larvae. Cross-correlation analysis indicated that post-yolksac larvae showed a periodicity in abundance around 12 h, which is similar to the period of the semidiurnal tide in the Bay. This indicates that post-yolksac larvae may utilize selective tidal st ream transport to effect retention in the estuary. Results of autocorr elation indicate that larval-patch diameter was approximately 3 km. Re sults of both cross-correlation and spectral analysis suggest that nei ther salinity nor sea level height serves as a cue for vertical migrat ion. Rather, some aspect of the tidal-velocity field appears to be imp ortant.