divided into 14 distinct matriarchal clones. For this 

 report, I consider only the five mtDNA size groups 

 that account for more than 95% of the variation in 

 Chesapeake Bay specimens. Molecular weight esti- 

 mates for the size groups (Fig. 1) were A = 17.5 

 kilobases (kb), B = 17.6 kg, C = 17.7 kb, D/E = 

 17.65/17.75, and F = 17.8. The D/E genotype in- 

 dicated individuals with two distinct molecules. 

 These genotypes were easily distinguished by the 

 migration of the lowest molecular weight fragment 

 produced by digestion with the enzymes mentioned 

 above. 



The distribution of mtDNA genotypes in males 

 taken from each of the collecting localities changed 

 dramatically from 1984 to 1986 (Table 1). In 1984, 

 the B genotype was found in more than 75% of the 

 specimens (81% in the Potomac, 53% in the Chop- 

 tank, and 100% in the Worton Point area). In 1986 



123456789 10 



Figure l.—Bcll digestion patterns oiM&rone saxatilis mtDNA 



showing size fragment variation for genotypes A = 17.5 kg, 



lanes 2, 3; B = 17.6 kb, lanes 4, 5; C = 17.7 kb, lanes 6, 7; 



D/E = 17.65/17.75, lane 8; and F = 17.8 kb, lane 9. Lanes 1 



and 10 are 1 kb ladder standards purchased from BRL, Inc. 



(Reference to trade names does not imply endorsement by the National 

 Marine Fisheries Service, NOAA.) 



this genotype represented about 30% of the spawn- 

 ing 1982 year class males (21% in the Potomac, 23% 

 in the Choptank, and 42% in the Worton Point area). 

 The C genotype represented 15% of the specimens 

 in 1984, but was more common in 1986 (49%). The 

 D/E and F genotypes were not observed in 1984, 

 but combined to represent 17% of the specimens 

 taken in 1986. The changes in mtDNA genotype fre- 

 quencies from 1984 to 1986 are highly significant 

 in the combined data and in the Worton Point and 

 Potomac spawning areas (Table 1). The nonsignif- 

 icant result in the Choptank may be due to the ef- 

 fects of pooling and inadequate sample size. 



Year to year variation in the frequencies of var- 

 ious mtDNA genotypes found among spawning 

 individuals could arise from changes in the age com- 

 position. Previously spawning individuals may die 

 and new recruits may be descendants of different 

 females. These possibilities are not concerns here 

 because data are reported only upon the 1982 year 

 class males. The changes in mtDNA frequencies 

 within spawning members of this group can be ex- 

 plained by either of three hypotheses. First, the 

 abundance of B genotypes in the 1984 sample may 

 be an overestimation of their actual frequency, but 

 the age at which male striped bass join spawning 

 aggregations may depend upon genetic factors that 

 are marked by (or perhaps linked to) mtDNA geno- 

 types. As the remaining genotypes became sexual- 

 ly mature, mtDNA frequencies among spawners 

 more accurately reflected the frequencies in the 

 1982 year class. Second, the 1984 data may actual- 

 ly reflect genotype frequencies during that year, but 

 differential mortalities from 1984 to 1986 substan- 

 tially altered the frequencies. This does not neces- 

 sarily imply selective mortalities because aggrega- 

 tions of B genotypes following the spawning season 

 may have been more susceptible to fishing pressure. 

 Third, the increase in the C, D/E, and F genotypes 

 may be the result of migration from other areas. The 

 survey of Chapman and Powers (unpubl. data) did 

 not find significant concentrations of these geno- 

 types in the Chesapeake Bay, but this survey did 

 not include the York and James Rivers in the Chesa- 

 peake Bay or the Hudson River. If these rivers are 

 the source of most of the C, D/E, and F genotypes 

 found in this study, it would require a migration rate 

 of 50% among Chesapeake Bay and/or the Hudson 

 River stocks to produce the frequency changes noted 

 here. 



Migratory patterns of M. saxatilis vary from 

 region to region along the Atlantic coast. Popula- 

 tions from southern North Carolina to the St. John's 

 River, FL, are essentially riverine and do not under- 



168 



