Ma. Smale et Cf. Rabeni, INFLUENCES OF HYPOXIA AND HYPERTHERMIA ON FISH SPECIES COMPOSITION INHEADWATER STREAMS, Transactions of the American Fisheries Society, 124(5), 1995, pp. 711-725
Indices of hypoxia and hyperthermia tolerance for Missouri fish assemb
lages were based on laboratory measurements of lethal dissolved oxygen
concentrations and temperatures, combined with field measures of the
relative abundances of tolerant and sensitive species. Fish assemblage
s and extreme physicochemical conditions were monitored over 3-4 years
at 18 sites on headwater streams in the Prairie, Ozark Border, and Oz
ark regions of Missouri. Oxygen minima ranged from 0.8 to 6.0 mg/L, an
d temperature maxima ranged from 19.6 to 30.7 degrees C; oxygen minima
at study sites were not correlated with temperature maxima. Hypoxia t
olerances of fish assemblages were strongly correlated with minimum st
ream oxygen concentrations and varied concordantly with regional, long
itudinal, and temporal gradients in stream oxygen minima. Hyperthermia
tolerances of fish assemblages were not correlated with maximum strea
m temperatures, nor were regional, longitudinal, or temporal differenc
es in hyperthermia tolerances concordant with variation in temperature
maxima. Axis scores from a detrended correspondence analysis of speci
es frequencies were strongly correlated with dissolved oxygen minima f
or all 18 sites, but axis scores correlated with temperature maxima on
ly at the four well-oxygenated sites. Low dissolved oxygen levels had
a substantial effect on the composition of fish assemblages at most si
tes, but maximum temperatures influenced assemblages only at the few s
ites without severe levels of hypoxia.