FISHERY BULLKTIN: VOL. 86, NO. 1 



and 1.75 cm/second shoreward). Based on that av- 

 erage shoreward advection rate we calculated 

 that larvae could be passively transported 98 km 

 in the onshore direction in 65 days. Examination 

 of length frequency and age at capture data 

 (Cowan, in press) suggest that larval Atlantic 

 croaker arrive in nearshore coastal waters, on the 

 average, 60-90 days after hatching. Most small, 

 newly hatched Atlantic croaker larvae were col- 

 lected approximately 100 km offshore. Although 

 the onshore component of advective transport is 

 small in comparison with the average alongshore 

 component, the estimate of shoreward transport 

 rate is reasonable when age of larvae is consid- 

 ered. 



CONCLUSIONS- 

 RECRUITMENT IMPLICATIONS 



Across-shelf transport appears to be an order of 

 magnitude smaller than alongshore advective 

 transport in the northwestern Gulf shelf waters 

 during winter and spring. Sciaenid larvae col- 

 lected offshore in the study area, at midshelf and 

 beyond, would probably be lost to the estuaries in 

 western Louisiana. Those offshore larvae would 

 be transported towards north Texas estuaries, or 

 back to the east if they were far enough offshore, 

 since there is evidence for an easterly counter 

 current (Kelly et al. 1982; Cochrane and Kelly 

 1986). 



Sand seatrout are common in west Louisiana 

 estuaries (Herke et al. 1984) and were the most 

 abundant sciaenid larvae collected in this study. 

 They spawn, in general, more inshore (Fig. 1) 

 than Atlantic croaker or spot. Conceivably, many 

 of the sand seatrout collected in the study area 

 inside the coastal boundary layer on the inner 

 shelf would have recruited to Louisiana estuaries. 



Still, large numbers of postlarval sciaenids, 

 other than sand seatrout, enter the estuaries in 

 west Louisiana each year. Atlantic croaker and 

 spot were the 3rd and 21st most abundant fish, of 

 117 species collected, in the Calcasieu River 

 Basin, the largest estuary in west Louisiana 

 (Herke et al. 1984). However, the distribution and 

 transport analyses indicate that most spot and 

 Atlantic croaker larvae directly offshore at least 

 would not have recruited to the Calcasieu Basin. 

 Interpretation of these data suggests that the 

 source of the sciaenid postlarvae shown to season- 

 ally recruit to the Calcasieu estuaries must be 

 east of the study area. Interpretation of data sum- 

 marizing several years of northern Gulf shrimp- 



trawl collections suggests that, during the spawn- 

 ing season, a sufficient concentration of adults 

 exists to the east of our study area (Darnell et al. 

 1983). 



In the fall and winter, high concentrations of 

 Atlantic croaker, and to a lesser extent spot, have 

 been found between the 20 and 40 m depth con- 

 tours (65 and 125 km offshore) in an area east of 

 the sampling grid. The area and timing of high 

 concentration coincides with the reported spawn- 

 ing location and period for both Atlantic croaker 

 and spot. If indeed this concentration represents a 

 spawning distribution, it would help explain why 

 so few Atlantic croaker and spot larvae, relative 

 to the number of juveniles seen in estuaries, were 

 collected in this and previous Gulf of Mexico 

 ichthyoplankton studies. Unless collections were 

 made in or near the spawning area, single-station 

 densities would be low as eggs and larvae were 

 dispersed. Furthermore, this study demonstrates 

 the need for understanding both biological (verti- 

 cal distribution, age and growth, behavior, etc. of 

 larvae) and physical (ocean currents, estuarine- 

 shelf exchange, etc.) processes which may influ- 

 ence estuarine recruitment. 



ACKNOWLEDGMENTS 



We would like to thank Wm. Wiseman, 

 L. Rouse, Jr., and S. Dinnel for their discussion 

 and assistance in interpretation of the physical 

 oceanographic data. We gratefully acknowledge 

 E. Turner, J. Geaghan, M. Fitzimmons, 

 B. Thompson, and W. Herke for critically review- 

 ing this manuscript. 



Funding was provided by a Louisiana Depart- 

 ment of Wildlife and Fisheries, U.S. Department 

 of Energy and LSU Center for Wetland Resources 

 cooperative agreement No. DE-FC96-81P010313. 

 Additional support was given by the Department 

 of Marine Sciences, Louisiana Sea Grant College 

 Program and the Coastal Fisheries Institute. 



LITERATURE CITATIONS 



Barger, L. E., and a. G. Johnson 



1980. An evolution of marks on hardparts for age 

 determination of Atlantic croaker, spot, sand seatrout, 

 and silver seatrout. U.S. Dep. Commer., NOAA Tech. 

 Memo. NMFS-SEFC-22, 5 p. 



Barger, L E , and M. L. Williams. 



1980. A summarization and discussion of age and growth 

 of spot, Leiostomus xanthurus Lacepede, sand seatrout, 

 Cynoscion arenarius Ginsburg, and silver seatrout, 

 Cynoscion nothus (Holbrook), based on a literature 

 review. U.S. Dep. Commer., NOAA Tech. Memo. 



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