Figure 2. Abundance and productivity of the pristine (1890) and
presentimpounded a n dunimpoundedwhitesturgeonstocks in
the lower Columbia River (Beamesderfer et al. 1995. DeVore et
al. 1995).
to restore sturgeon populations tohistoriclevels of
productivity. Vore et al.1995).
Figure 3. Relations betweenriver discharge, availability of
spawninghabitat, andannualrecruitment(BonnevilleReser-
voironly) forwhilesturgeon in thelowerColumbia River
(adapted fromParsley & Beckman 1994).350 000 kg, and support 145 000angler trips (De-Currentsturgeonbiomass in theunimpounded
234 km of the lower ColumbiaRiverappearssimi-
A Columbia River example lar to levelsduring pristine conditionsprior to sig-
nificantexploitation in thelate1800s(Figure 2).
The ColumbiaRiver whitesturgeon populations UpstreamfromBonnevilleDam, aseries of main-
represent atypicalsituationwherehabitatchanges stemdamshavetrappedstocks of whitesturgeon in
havedrasticallyaffected the stock, harvest hasbeen aseries of reservoirs. Individual white sturgeon
regulated, supplementationstocking isbeing con- rangeextensivelythroughouteach reservoir but
sidered, butonlyhabitatchanges can beexpected to rarelypassupstream or downstream dams(North
restore sturgeonproductivity to historic levels. etal. 1993). Allreservoirs arcsimilar inthathydr-
Only an accident of engineeringprevented the Co- ologicretentiontimes arcshort,littoral zone islim-
lumbia River population ofwhite sturgeon from ited, and current is measurablemost of theyear.
joining theother threatened andendangeredstur- However,reservoirsvary insize,depth,substrate,
geon and paddlefish populationsthroughout the andlength of thefree-flowingportion in thetail-
world. In1983 Bonneville Dam wascompleted in water of theupstreamdam.
the gorgewhere theriver cutsthrough theCascade ColumbiaRiverreservoirsprovide a laboratory
mountainrange. If this dam hadbeenbuilt at the forexamininglimitingfactors for whitesturgeon.
bottom of thegorge just 5milesdownstream, it Eachstock ispresented with adifferentarray of
wouldhave flooded or blockedaccess tocritical habitat conditions which affect reproduction,
spawninghabitat and destroyedproductive c o n- growth, andsurvival and inturnregulate popula-
mercial andsportsturgeon fisheries in thelower riv- tionsize and productivity. Fish that historically
e r which annually produce 45 000 fish, yield moved throughoutthisarea to usescattered re-
sources are nowtrapped in areservoirwhich n o