variables are closely correlated and provide no con-
clusions regarding salinity. However, results of
stocking 2-9 week old fish in the Savannah River
also indicated rearing distance upstream may affect
survival. Fish released and presumably reared be-
tween river km 103-273, upstream of head-of-tide
(river km 83), had an adult return rate of 1.3%,
while fish stocked at river km 65-58, downstream of
head-of-tide, had a 0.4% return rate (Smith et al.
1995). In the Savannah River, salinity penetrates in
summer to river km 36, but contact of stocked YOY
with salinity was not monitored. Smith et al. (1995)
speculated that different acclimation and imprint-
ing times produced the different returns. There is
insufficient information for firm conclusions, but
evidence in the present report indicates that rearing
location upstream is important for survival of early
life stages and population abundance.would not change the basic relationships. Abun-
dance of the Saint John River population, whose
migration is likely blocked, would be located well
below the new regression line. In general, the two
southern rivers (Altamaha and Pee Dee) do not fit
the pattern of the northern and north-central rivers,
and neither would the Savannah River, even with
enhanced abundance due to stocking. Perhaps,
abundance of southern populations is not related to
spawning location, but their spawning locations are
far upriver, like northern populations. The low
abundance of southern adults may be affected more
by anthropogenic impacts than by spawning loca-
tion. More research is needed to understand factors
that affect abundance of southern populations.
Why do females have a strong behavioral drive to
move to river km 200-300 km to spawn? Perhaps,
the behavior is related to finding suitable substrate
and bottom velocity for spawning. However, in the
Connecticut River these habitat conditions are
available at downstream reaches, particularly En-
field Rapids, Connecticut, at river km 110. But pres-
pawning fish continue upstream until blocked by
Holyoke Dam. Migration patterns previously dis-
cussed suggest that three behavioral patterns of
shortnose sturgeon insure that early life stages rear
far upstream: (1) spawning females migrate far up-
stream, (2) larvae migrate a short distance, and (3)
YOY are non-migratory for about 1 year. The be-
havior of females, larvae, and YOY may be adapta-
tions that insure young fish do not contact salt water
until salinity tolerance develops. Larvae may also
gain a survival advantage from predators by delay-
ing downstream migration until they are larger.
Superior survival of fish reared upstream of salt-
water is supported by two kinds of information.
Least squares linear regression comparisons of 10
rivers for relationships between adult abundance
and two independent variables, (1) distance from
spawning location to head of tide, and (2) distance
from spawning location to salt water (maximum in-
trusion of salinity) found significant relationships
with both factors (respectively, r^2 = 0.88, p < 0.0005,
r^2 = 0.75, p < 0.025). The relationship with head of
tide was particularly strong. Both analyses support
the hypothesis of increased survival associated with
spawning distance upstream, but both independent
Survival and recruitmentThere is only limited information on survival of
early life stages. Richmond & Kynard (1995) found
that substrate with abundant crevices is likely crit-
ical for survival of eggs and embryos. Mortality of
eggs due to the fungusSaprolegnia,although high in
cultured eggs, was only 8% (mean of five daily sam-
ples of mid-developed eggs) at a Connecticut River
spawning site (M. Horgan & B. Kynard unpublished
data). Fish predation on eggs at the same spawning
site also was insignificant. No data are available on
mortality of embryos or larvae, but losses due to
predation and unsuccessful initiation of feeding are
probably high in these motile life periods. Year-
class strength is likely established early in life, prob-
ably within 1-2 months.
Dredging in freshsaltwater reaches of rivers con-
taining shortnose sturgeon may destroy or alter ju-
venile and adult habitat. Fish may also be impinged.
No adults were impinged during evaluations done
in the Delaware River (Hastings^17 ), but nothing is(^17) Hastings, R.W. 1983. A study of the shortnose sturgeon (Aci-
penser brevirostrum population in the upper tidal Delaware Riv-
er: assessment of impacts of maintenance dredging. Final Report
to U.S. Army Corps of Engineers, Philadelphia. 29 pp.