Daniel and Graves: Morphometry and genetic identification of sciaenid eggs 



259 



07 0.7250750775 08 08250.850875 09 09250950975 1 1025105107511 1125 



Outside Egg Diameter (mm) 



B. chrysoura | | C. regalis 



P. cromis 



Figure 3 



Size distributions of all eggs morphologically typed as sciaenids and identi- 

 fied using genetic techniques. 



wise, measures of spawning stock 

 biomass will be similarly over-es- 

 timated, results that could signifi- 

 cantly impact management deci- 

 sions. Comparable biases in esti- 

 mates of egg production and 

 spawning stock biomass of weak- 

 fish could result from egg mis- 

 identifications. However, the more 

 protracted spawning season and 

 greater area of spawning for 

 weakfish in Chesapeake Bay 

 (Olney, 1983) would make these 

 impacts much less severe. 



Biochemical techniques are 

 an important tool for the fur- 

 ther study of eggs of sciae- 

 nids. Genetic analysis has the 

 potential to produce reliable 

 results and permit the stor- 

 age of samples for later analy- 

 sis. Additional studies are 

 needed to survey genetic 

 identifications over the entire 

 spawning season and area to 

 determine if egg sizes change 

 over time or are influenced by 

 seasonal changes in hydrog- 

 raphy or by age structure of 

 the spawning stock. Finally, 

 the use of genetic techniques, 

 coupled with an extensive ex- 

 amination of morphology 

 could lead to the delineation 

 of other characters that may 

 be useful in separating the 

 eggs of these species. 



Acknowledgments 



lower Chesapeake Bay based on OED are subject to 

 error. These findings are particularly timely in light 

 of the increased use of fishery-independent assess- 

 ments of stock size that require precise estimates 

 of egg abundance (egg production method). Because 

 eggs of black drum and weakfish are spatio-tempo- 

 rally coincident and OEDs overlap, estimates of egg 

 production by black drum in lower Chesapeake Bay 

 may be over-estimated by 50% or greater if identi- 

 fication criteria are based solely on egg size. Like- 



J. McGovern, M. Cavaluzzi, 

 J. Field, C. Baldwin, and K. 

 Kavanaugh kindly assisted 

 with sample collection. P. Crewe patiently processed 

 plankton samples at sea and in the laboratory, and 

 J. McDowell provided valuable technical assistance 

 with mtDNA analyses. J. Olney helped in the de- 

 sign and implementation of the sampling program 

 and provided comments on the manuscript. Addi- 

 tional reviews were provided by J. Musick, J. 

 Cowan, and E. Heist. This study was funded in part 

 by the Virginia Marine Resources Commission un- 

 der U.S. Fish and Wildlife Contract F-95-R. 



