640 



Fishery Bulletin 89(4), 1991 



or deviations from a proposed pattern can result from 

 sample "snapshots" being taken at different times of 

 an ongoing process. Use of a current drogue as a 

 reference marker for the collection of plankton samples 

 in our study increased the probability of staying with, 

 and repeatedly sampling, a particular patch of red 

 drum larvae. This was clearly the case in cruise 84-9-1, 

 when both larval abundance and size composition re- 

 mained essentially unchanged throughout the duration 

 of the cruise. Use of a reference marker does not, 

 however, invariably ensure that a particular population 

 will continue to be sampled. During cruise 85-9-1, the 

 change in size composition of larvae in the morning 

 sampling period indicated that a different patch of 

 larvae was being sampled. Nonetheless, a drifting or 

 Lagrangian sampling design would be more likely to 

 yield an accurate description of diel vertical movements 

 than the more typical ichthyoplankton survey design 

 where collections are made at varying times and loca- 

 tions. Sampling designs based on fixed stations are 

 more appropriate for resource surveys when observa- 

 tions from large geographic areas encompassing all or 

 most of a species' spawning grounds are needed to 

 estimate spawner biomass from the abundance of eggs 

 and/or larvae. 



Acknowledgments 



We gratefully acknowledge the significant contribu- 

 tions to this study by the following individuals. H.D. 

 Howse (Gulf Coast Research Laboratory), J.I. Jones 

 (Mississippi-Alabama Sea Grant Consortium), and A. 

 Kemmerer (National Marine Fisheries Service) who 

 provided long-term encouragement and monetary sup- 

 port. R.I. Shulman handled key aspects of this project 

 from training and supervision of plankton sorters to 

 database management. J.T. McBee and W. Brehm 

 wrote computer software for field sensors and data log- 

 gers and, along with J.A. McLelland, assisted in the 

 field. Numerous staff members of the Gulf Coast 

 Research Laboratory and Mississippi Bureau of Marine 

 Resources participated on our cruises. Finally, the cap- 

 tain and crew of the RV Tommy Munro provided con- 

 sistent cooperation and helpful ingenuity. B.H. Comyns 

 reviewed the manuscript and offered useful ways to 

 improve it, as did two anonymous reviewers. The study 

 was sponsored in part by the National Oceanic and 

 Atmospheric Administration Office of Sea Grant, under 

 grant NA85AA-D-SG005, and the Mississippi- Alabama 

 Sea Grant Consortium and Gulf Coast Research 

 Laboratory. 



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