Powell et al.: Modeling oyster populations 



369 



20 



4 5 6 7 

 Size Class 



 Sumter Mortality 

 D Winter Mortality 



3 4 5 



Julian Year 



E 



 Summer Mortality 

 Q Winter Mortaflty 



3 4 5 



Julian Year 



1000 



_ 800 



400 



200 



1 23456789 10 

 Size Class 



I) 



 Summer Mortaflty 

 n Winter Mortality 



2 3 4 



Julian Year 



Z 20 - 



Figure 1 8 



A comparison of the final size-fre- 

 quency distributions (day 2,160) 

 (A and B), the yearly reproduc- 

 tive efforts (C, D, and E) and the 

 number of market-size individu- 

 als in the Crassostrea virginica 

 population after 6 years (F) for 

 the simulations depicted in Fig- 

 ure 17. (A) mortality restricted to 

 the summer (Fig. 17, A, C, and 

 E). (B) mortality restricted to the 

 winter (Fig. 17, B, D, and F). (C) 

 Yearly reproductive effort for 

 populations exposed to mortality 

 in sizes 5 and larger (Fig. 17, A 

 and B). (D) Yearly reproductive 

 effort for populations exposed to 

 mortality in sizes 6 and larger 

 (Fig. 17, C and D). (E) Yearly re- 

 productive effort for populations 

 exposed to mortality in sizes 7 

 and larger (Fig. 17, E and F). (F) 

 The number of market-size indi- 

 viduals in the population after 6 

 years, restricting the calculation 

 of market-size individuals to the 

 same classes suffering mortality, 

 5 and larger (sum-5. Fig. 17A; 

 win-5, Fig. 17B), 6 and larger 

 (sum-6, Fig. 17C; win-6, Fig. 17D) 

 and 7 and larger (sum-7, Fig. 

 17E; win-7, Fig. 17F). 



populations exist under different physiological con- 

 straints and these constraints demand different 

 management philosophies and decisions. 



Acknowledgments 



We thank Elizabeth Wilson-Ormond and Stephanie 

 Boyles for help in data acquisition. This research 

 was supported by an institutional grant NA89-AA- 

 D-SG139 to TAMU by the National Sea Grant Col- 

 lege Program, National Oceanic and Atmospheric 

 Administration (NOAA), U.S. Department of Com- 

 merce, grant DACW64-91-C-0040 from the Army 

 Corps of Engineers, Galveston District Office, and 

 computer funds from the College of Geosciences and 

 Maritime Studies Research Development Fund. 



Additional computer resources and facilities were 

 provided through the Center for Coastal Physical 

 Oceanography at Old Dominion University. We ap- 

 preciate this support. 



Literature cited 



Andrews, J. D., D. Haven, and D. B. Quayle. 



1959. Fresh-water kill of oysters {Crassostrea 

 virginica) in James River, Virginia, 1958. Proc. 

 Natl. Shellfish. Assoc. 49:29-49. 



Andrews, J. D., and W. G. Hewatt. 



1957. Oyster mortality studies in Virginia. II: The 

 fungus disease caused by Dermocystidium 

 marinum in oysters in Chesapeake Bay. Ecol. 

 Monogr. 27:1-26. 



