their ages varied by as much as 19 years (Zweiacker
1967).
The shovelnose sturgeon is the smallest of the
North American sturgeons. Carlander (1969) indi-
cates a maximum weight for the shovelnose stur-
geon of 4.5 kg with most specimens being less than
2.5 kg. Shovelnose sturgeon in the upper Missouri
River, however, are notably larger than specimens
throughout most of its range. Peterinan & Haddix
(1975) examined 427 shovelnose in Montana and
found an average weight of 2.4 kg; 11% of the indi-
viduals weighed more than 3.6 kg, 5% more than 4.5
kg. and specimens up to 7 kg were found. Keenlyne
et al. (1994) found significant morphometric differ-
ences between upper Missouri River fish compared
to downriver populations which suggests that a dif-
ferent strain of shovelnose sturgeon exists in the up-
per Missouri River.
Food, growth, and reproduction Spawning habitat of shovelnose sturgeon has not
been described. Spawning is believed to occur over
Shovelnose sturgeon are opportunistic feeders that hard substrate in primary tributary streams to the
prey on aquatic invertebrates, primarily immature main rivers (Cross 1967, Peterman & Haddix 1975,
insects (Hoopes 1960, Held 1969, Ranthum1969, Christenson 1975, Elser et al. 1977) or along the bor-
Elser et al. 1977, Modde & Schmulbach 1977, Dur- ders of the main river channels (Coker 1930, Moos
kee et al. 1979, Carlson et al. 1985). Several studies 1978). Studies conducted before major modifica-
indicate that the abundance of food affects growth tions were made to river channels and tributary
rates of shovelnose sturgeon. Altered stream flows flows concluded that shovelnose sturgeon swam up
affect both the ability of shovelnose sturgeon lo find tributaries to spawn (Forbes & Richardson 1920,
food (Modde & Schmulbach 1977) and the abun- Coker 1930). Moos (1978) stated that shovelnose
dance of prey organisms (Elser et al. 1977). sturgeon only used tributaries infrequently and
Carlander (1969) summarized shovelnose stur- chose to remaininthe larger rivers. Cross (1967)
geon growth data from fish collected from the Mis- suggested that shovelnose sturgeon may seek trib-
souri River as the reservoirs were filling. and found utary streams for spawning when flows are high.
them to be 213 mm total length (TL) at age 1, 274 Moos (1978) observed that shovelnose sturgeon
mm at age 2,399 mm at age 5, and 503 mm at age 10. moved up to 540 km and stated that dams have
In a study on the Mississippi River,Helms (1973) probably prevented movement to traditional
found shovnose sturgeon to be 211 mm fork length spawning areas, contributing to a lack of recruit-
(FL) at age 1, 328 mm at age 2. 495 mm at age 4.592 ment since damming of the upper Missouri River.
mm at age 6, and 701 mm at age 10,Even though Although actual spawning has not been de-
lengths of the Missouri River fish were in total scribed, the capture of fish in spawning condition
length and the Mississippi River fish in fork length. indicates that shovelnose sturgeon spawnfrom late
the Missouri River fish were much shorter at given April to June (Forbes & Richardson 1920, Coker
ages. Zweiacker (1967) found that Missouri River 1930, Eddy & Surber 1947, Barnickol & Starrett
shovelnose sturgeon nearly ceased growing and re- 1951, Christenson 1975, Elser et al. 1977, Moos 1978)
producing alter the Missouri River dams were con- at water temperatures between 16.9 and 20.5 °C
structed. Shovelnose sturgeon from 8 to 27 years of (Christenson 1975, Elseretal. 1977). Most males be-
age were all about the same length, even though come sexually mature at age 5, while most femaleswere considered a nuisance to commercial fisher-
men and were destroyed when caught (Coker 1930).
Barnickol & Starrett (1951) indicated that the de-
cline of the shovelnose sturgeon in the Mississippi
River also coincided with the development of the
river as a navigation canal. The abundance of shov-
elnose sturgeon has been estimated for rivers of
several sizes with a variety of habitats and varying
degrees of modification: Schmulbach (1974) esti-
mated 2500 fish km–1for the unchannelized Missou-
ri River. Helms (1972) estimated 1030 fish km–1for
the navigation-altered Mississippi River. Christen-
son (1975) estimated 100 fish km–1for the small Red
Cedar River in Wisconsin, and Elser et al. (1977)
estimated 403 to 537 fish km–1for the Tongue River
in Montana.