Operational Plan for the Restoration of Diadromous Fishes to the ...

populations, Waldman et al. (1996) use mtDNA to examine population structure of
shad from the Connecticut, Hudson and Delaware Rivers. They found that the
populations from these rivers were extremely diverse showing no significant
heterogeneity in the mtDNA frequencies. They surmised that gene flow among
neighboring American shad populations are too great to allow differentiation.
Results were similar in studies using microsatellite DNA. Julian and Bartron (2008)
used mtDNA and microsatellite data to examine American shad population structure
on the Susquehanna, Delaware and Hudson Rivers. They determined that the shad
populations in these three rivers were not significantly differentiated from each other
because of the lack of numerous distinct haplotypes in the mtDNA and lack of
differentiation in the microsatellite data (pairwise FST between 0.001 and 0.0026).
However, the lack of significant population differences observed in the three rivers
was not unexpected given the high levels of exogenous stock transfer. Waters et al.
(2000) found that both mtDNA and microsatellite DNA were able to distinguish subtle
differences for the Atlantic coast for populations of American shad from the James,
Pamunkey and Hudson Rivers (FST ≈ 0.01 for certain loci and FST=0.0063 for all loci).
Straying among these rivers (3.9 to 71.2 breeders per generation, depending on
calculation method) was sufficient to permit only marginal population differentiation.
These results may be conservative given that weak differentiation was detected with
a low number of markers (5 microsatellite loci).
Unpublished results from Bentzen (personal communication, December 3, 2008) for
shad populations in rivers of the Bay of Fundy have shown moderate to great
differentiation (FST values up to 0.07, or corrected for the high heterozygosity up to
0.24). Based on this data, he believes that genetically effective straying in shad
must be very low.
Waters et al. (2000) also compared an introduced, non-native shad population from
the Columbia River (OR, WA) to the Hudson River stock, its source population.
Their study found that the Columbia River population was highly differentiated from
the Atlantic Coast populations. Shad is a recent invader to the Columbia River,
introduced in the late 19 th century. Rottiers et al. (1992) noted significant differences
in the growth and behavior and temperature and salinity tolerance of juvenile shad
from the Columbia and Delaware Rivers. The Columbia River fish grew significantly
faster, attained a greater final weight, and had lower mortalities at all the test
salinities and temperatures than the Delaware River fish. This example suggests
that changes to the shad population structure may occur relatively soon (within 20
generations) after an introduction.
Management Experience
A number of states currently use or have used exogenous fish transfers and/or
hatchery supplementation to restore American shad (ASMFC 1999; ASMFC 2007a;
Hendricks 2003). This management practice is well established and is incorporated
in the ASMFC definition for restoration (ASMFC 2007a). In the New England states,
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