Waldman et al.: Population bottlenecks and DNA diversity in Morone saxatilis 
617 
Table 2 
Mitochondrial DNA composite haplotype frequencies (letters represent length polymorphisms; numerals represent site polymor- 
phisms; percentages in parentheses) and genotypic diversity indices. 
Haplotype 
Population 
N 
A-l 
A-2 
B-l 
B-2 
C-l 
C-2 
D-l 
D-2 
cjunuuypic 
diversity 
Hudson River 
110 
3 
(0.03) 
2 
(0.02) 
25 
(0.23) 
7 
(0.06) 
19 
(0.17) 
32 
(0.29) 
17 
(0.15) 
5 
(0.04) 
0.810 
San Francisco Bay 
63 
4 
(0.06) 
4 
(0.06) 
51 
(0.81) 
2 
(0.03) 
2 
(0.03) 
0.340 
Coos Bay (wild) 
38 
38 
(1.0) 
0.0 
Coos Bay (hatchery) 
27 
27 
(1.0) 
0.0 
Umpqua River 
12 
11 
(0.92) 
1 
(0.08) 
0.167 
tein level both within and among populations (re- 
viewed in Waldman et al., 1988). For example, Otto 
(1995) reported mean heterozygosity levels of Atlan- 
tic striped bass of approximately 1.0%, and 0.75% 
for the Hudson River population. Very low genetic 
diversity for Atlantic coast striped bass has also been 
shown by several mtDNA studies (Chapman, 1990; 
Wirgin et al., 1990, 1993; Waldman and Wirgin, 
1994). For example, Wirgin et al. (1990) estimated 
the proportion of nucleotides that differed for the 
most divergent individuals among mid-Atlantic 
striped bass stocks at 0.0004, one of the lowest val- 
ues for any animal species. What mtDNA variation 
does exist in striped bass primarily is length, rather 
than site variation (Waldman and Wirgin, 1995). 
Four mtDNA major length variants have been found 
in striped bass from the Hudson River (Wirgin et al., 
1990, 1993; Waldman and Wirgin, 1994). 
Thus, the substrate of genetic variation available 
among striped bass from the Hudson River and other 
Atlantic coast estuaries was extremely low in com- 
parison with most fishes (e.g. Waldman et al., 1996). 
From this unusually narrow gene pool some 430 or 
so yearlings were collected and transplanted in 1879 
and 1882 to San Francisco Bay. It is not known how 
many of the female yearlings survived to reproduce 
as founders of all Pacific coast striped bass, but about 
215 represents an approximate upper limit (assum- 
ing an unrealistic 100% survival rate), and 5 the 
lower limit, given the 5 haplotypes detected. Esti- 
mates of annual expectation of death from natural 
causes of the San Francisco Bay striped bass popu- 
lation obtained during a period of exploitation (sum- 
marized in Westin and Rogers 3 ) ranged between 0.31 
and 0.12, and averaged about 0.2. Moreover, female 
striped bass have variable maturation schedules 
(Berlinsky et al., 1995); in San Francisco Bay, it has 
been found that females mature at ages 4 and 5 
(Stevens et al., 1987). Therefore, a more reasonable 
estimate for the number of transplanted females that 
survived to found the San Francisco Bay striped bass 
population is about 100. 
Striped bass then appeared in Coos Bay some 35 
years after their introduction to San Francisco Bay. 
It is not possible to determine the number of founders 
of the Oregon populations nor their initial genetic 
makeup. Present Oregon striped bass are restricted to 
mtDNA length haplotype C. It is not known what the 
mtDNA haplotype frequencies of the San Francisco Bay 
stock were circa 1915, but if their present haplotype 
frequencies are used as an approximation, then the 
chance of a single female founder having a haplotype 
other than the C haplotype is only 16%. We believe 
that given the historical scarcity of striped bass in north 
Pacific coastal waters (Forrester et al., 1972) and the 
concordance between the dominant haplotype of the 
San Francisco Bay stock and the single (major length 
variant) haplotype of the Coos River and Umpqua River 
stocks, it is reasonable to assume that the Oregon popu- 
lations were founded by one or a very low number of 
female striped bass with the C-haplotype. 
Founding of the Oregon striped bass populations 
by a limited number of females from California, fol- 
lowing the initial bottleneck of transplantation from 
the Atlantic, would have resulted in a greatly reduced 
level of genetic variation in comparison with the 
3 Westin, D. T., and B. A. Rogers. 1978. Synopsis of biological 
data on the striped bass, Morone saxatilis (Walbaum) 
1792. Technical Report 67, Graduate School of Oceanography, 
Univ. Rhode Island, 154 p. 
