Figure 2.Comparison of seven northern and north-central pop-
ulations with five southern populations for adult abundance. Es-
timates for populations in the Cape Fear anti Santee-Cooper riv-
ers are expert opinions.
unpublished data). Additional study may find the
Hudson River population even larger than 38 000.
Abundance of adults has been estimated for a to-
tal of seven populations in northern or north-cen-
tral rivers and for five southern populations. Abun-
dance varies From tens of thousands (Saint John,
Hudson, and Delaware rivers) to lens in the Merri-
mack and Cape Fear rivers (Table 1). The great
abundance of adults in the Delaware River suggests
that large populations were likely present in other
large rivers, like the Potomac and Susquehanna riv-
ers, located at the center of the range. For the past
100 years, a dissolved oxygen block at Philadelphia
has prevented most spring and summer up- or
downstream migration of fishes (Chittenden 1974).
This pollution block may also have prevented
shortnose sturgeon from using the estuary and em-
grating to nearby rivers in Chesapeake Bay. Adultshortnose sturgeon in the Delaware River are pres-
ently restricted to only 75 km (Brundage & Mead-
ows1982, Hastings et al. 1987, O’Herron et al. 1993).
Recent improvement in water quality may result in
renewed access of shortnose sturgeon to the lower
Delaware River and tidal interface (an additional
100 km), and could result in a dramatic increase in
abundance. It may also provide emigrants to recol-
onize those Chesapeake Bay rivers that have suit-
able habitat.
Adult abundance is significantly higher in north-
ern populations than in southern populations
(Mann Whitney Test, one tail, p <0.02,Figure 2).
This difference may reflect a historical pattern of
smaller southern populations due to intrinsic differ-
ences in river characteristics. But Rogers & Weber^4
believe that a relatively pristine large southern river
like the Altamaha River, Georgia, should support
more than 650 adults. All natural southern popula-
tions are below or near the minimum viable pop-
ulation level of 1000 adults suggested for verte-
brates (Thompson 1991).
Anthropogenic factors are likely responsible for
the present low abundance of shortnose sturgeon in
southern rivers. All surveyed southern populations
are exposed to three or more of the following im-
pacts: harvest (bycatch and poaching), dams, river
flow regulation, pollution (particularly, paper mill
effluent), and dredging of fresh/saltwater interface
reaches. Most southern rivers have never been sur-
veyed well for shortnose sturgeon, or not in many
years. Recent surveys of two Georgia rivers found
degraded water quality and other impacts; short-
nose sturgeon were absent in both (Table 1). The
status of shortnose sturgeon in the St. Johns River,
Florida. is unknown, but a remnant population may
be present. The southernmost limit of shortnose
sturgeon distribution that has been recently docu-
mented is the Altamaha River, Georgia.
The Savannah River was stocked with more than(^4) Rogers, S.G. & W. Weber. 1995. Status and restoration of Atlan-
tic and shortnose sturgeons in Georgia. Report of Georgia Dept.
Nat. Resources. 28 pp.
(^5) Even the most well-designed and carefully managed fish cultur-
ing methods inherently (and often unintentionally) select certain
types of individuals that may or may not be adapted for condi-
tions in the wild.