Sturgeon biodiversity and conservation

408
sturgeon life history. Sturgeon are uniquely adapt- variety of prey and switch as prey availability
ed to the large mainstem river systems upon which changes. These fish can also withstand long periods
all species rely during all or part of their life cycle of starvation during periods of low food availability
(Rochard et al. 1990). Rivers include diverse hab- or spawning migrations (Dadswell 1979, Mason &
itats which are distributed in large scale patterns Clugston 1993). Sturgeon generally feed on invercorresponding
to the surrounding topography. Typ- tebrates in the benthic food chain (Held 1969, Dadical
transitions include headwaters through tribu- swell 1979, Carlson et al. 1985, Sandilands 1987,
taries. mainstem, and estuary into an ocean, sea, or McCabe et al. 1993) where most production occurs
large lake. In large basins, rivers may traverse many in large river systems (Sheehan & Rasmussen 1993).
different regions and climatic zones. Rivers are also Fish may also be an important diet component of
extremely dynamic habitats featuring large season- some sturgeon species (Semakula & Larkin 1968).
al and annual variations in physical conditions and Large sturgeon can consume large prey. Pursuit and
resource availability (Sheehan & Rasmussen 1993). capture of active prey belie an image of sturgeon as
Seasonal cycles in weather and runoff drive changes sluggish bottom scavengers.
in velocity. morphometry, temperature, substrate, Populations of sturgeon are buffered from anand
turbidity. Conditions vary from year to year in nual variation in environmental conditions by deunpredictable
patterns based on regional weather layed maturation, longevity, and high individual fepatterns.
Periodic floods and droughts may radical- cundity. Delayed maturation (Roussow 1957,
ly alter the riverine environment. Distribution and Sunde 1961, Dadswell 1979, Conte et al. 2 , Chapman
abundance ofmany species of fishes and other orga- 1989, Guenette et al. 1992, Keenlyne & Jenkins
nisms vary widely in response to spatial and tempo- 1993) speeds growth to large sizes as energy is deral
patterns. For instance, anadromous fishes are voted to somatic rather than gonadal development.
seasonally abundant as they move between spawn- Large size helps reduce predation. lowering natural
ing and feeding areas in portions of many temperate mortality rate and increasing longevity. A long liferivers
and estuaries.
span (Pycha1956.Wilson 1987, Rien &Beamesder-
Sturgeon have evolved life history characteristics fer 1994) allows fish numerous opportunities to
which allow them to thrive in these large, diverse. spawn and reduces the need to spawn in years when
and dynamic river systems. Individuals often range conditions are not suitable. Many species have been
widely to take advantage of scattered and season- observed to resorb eggs under these conditions
ally abundant resources. Regular migrations for (Artyukhinetal. 1979, Chapman 1989). Highfecunspawning
and short-term movements for feeding dity associated with large size improves spawning
have been observed for many species (Chadwick success in years when suitable conditions are en-
1959, Miller 1972a, Haynes et al. 1978, Haynes & countered.
Gray 1981, Smith 1985, Wooley & Crateau 1985, Many sturgeon species depend on free-flowing
Sandilands 1987, Kempinger 1988, Odenkirk 1989, rivers and seasonal floods to provide suitable
Hall et al. 1991, Mosindy & Rusak 1 , O’Herron et al. spawning conditions. Adhesive eggs are typically
1993). Many species are euryhaline and move freely broadcast over rocky substrates in turbulent. highbetween
freshwater, estuaries, and saltwater (Ro- velocity areas during high spring runoff (Magnin
chard et al. 1990) to further broaden their resource 1966, Buckley & Kynard 1985, Smith 1985, Kempbase.
Long-distance movements are facilitated by inger 1988, Hall et al. 1991, Mosindy & Rusak1, Latheir
large size, shape, and swimming ability which Haye et al. 1992, Parsley et al. 1993). Recruitment
allow them to move through heavy current.
Sturgeon are opportunistic predators that eat a
1 Mosindy, T. & J. Rusak. 1991. An assesment of lake sturgeon
populations in Lake of the Woods and the Rainy River 1987–90
Ontario Ministry of Natural Resources 66 pp.
, 2
Conte, F.S., S.I. Doroshov & P.B. Lutes. 1988. Hatchery manual
for the white sturgeon Acipenser transmontanus Richardson
with application to other North American Acipenseridae. University
of California Cooperative Extension Publication 3322.
104pp.