Figure1.Lateral view of adult male shortnose sturgeon Acipenser brevirostrum (94 cm IL) from the Connecticut River, Massachusetts,
U .S.A.
often reveals patterns that are not obvious, and can
lead to identification of adaptations and evolution-
ary processes (Frank & Leggett 1994). This report
summarizes much of the information on shortnose
sturgeon life history, examines latitudinal variation
in anadromy and spawning migrations, investigates
impacts of dams on spawning migration and abun-
dance, and reviews threats to the species. Explana-
tions that are proposed for behavioral patterns will
hopefully stimulate discussion and testing of hy-
pot h eses.
estuary. The lack of marine movements by most
adults suggests that the recolonization rate of short-
nose sturgeon to rivers where they have been extir-
pated would be slow. The lack of evidence for suc-
cessful recolonization of any river where shortnose
sturgeon was extirpated byAtlantic sturgeon fish-
eries and dams 100 years ago in the mid-Atlantic
(Ryder 1890, Smith 1985), supports the hypothesis
of a slow recolonization rate.
Rare individuals that are occasionally captured
at sea near the coast (review by Dadswell et al. 1984)
could represent emigrants that colonize new rivers
and maintain gene flow among populations. The
Range and colonization phenomenon of marine migrants is not understood.
but available information on marine captures in
The present range of shortnose sturgeon is disjunct, northern and southern parts of the range presented
with northern populations separated from southern by Dadswell et al. (1984), and corrected for misiden-
populations by a distance of about 400 km near the tified North Carolina captures by Ross et al. (1988),
geographic center. No known populations occur indicates a greater incidence of marine emigrants in
from the Delaware River, New Jersey, to the Cape the north compared to the south. Because northern
Fear River, North Carolina (Table 1). Historically, populations are also larger than southern popula-
populations were likely present in all large rivers in tions, there may be a relationship between popula-
this area,which includes Chesapeake Ray (Dad- tion size and number of marine emigrants. If this is
swell et al. 1984). Because the separation distance is so, only a large population like the Hudson River
great between northern and southern populations, population may be providing emigrants.
there may be no interchange of adults. Density dependent regulation of population
Unlike adult Atlantic sturgeon that range widely abundance that depends on emigration of fish in re-
along the coast (Murawski & Pacheco^1 ), most short- lation to food abundance is found in stream dwell-
nose sturgeon adults remain in their natal river or ing salmonids. and may be present in other fishes
that have limited movements and a restricted range
(Frank & Leggett 1994). Populations of shortnose
sturgeon have limited movements and a restricted
home range within their river and estuary. Further
young sturgeon have a size dependent dominance
(^1) Murawski, S.A. & A.L. Pacheco 1977. Biological and fisheries
data on Atlantic sturgeon, Acipenser oxyrhynchus (Mitchill).
Nat. Mar. Fish Serv., Sandy Hook Lab., Sandy Hook. Tech.
Report No. 10. 78 pp.