Large River Fish ~ 10,000 species > 2,000 species in Amazon (not all unique) Ancient freshwater fishes are river fishes.

Large River Fish

• ~ 10,000 species

• > 2,000 species in Amazon (not all unique)

• Ancient freshwater fishes are river fishes

Factors Influencing Distribution/Diversity

• Current Velocity

• Substrate

• Refugia

• Habitat– “normal”– Spawning– Seasonal

• Biodiversity

Raibley et al. (1997)

• Winter habitats used by largemouth bass in the Illinois River. N. Amer. J. Fish. Mgmt.

• Radio-tagged fish in Illinois River

• Tracked through different seasons and electroshocked

Most winter sites are man-made. Why?

Wintering Sites

• Current velocities lower– Winter site 2 cm/sec– Channel 19 cm/sec

• Temperatures higher– Springs– Industrial outflows

• Dissolved oxygen remains high

Most winter sites are man-made. Why?

Boys and Thoms (2006)

• A large-scale hierarchical approach for assessing habitat associations in large dryland rivers. Hydrobiologia

• Effects of scale on distribution and diversity of fishes

Zone 1 very different Zones 2 and 3, not zone 4fewer fish, higher abundance native species

Zone 2 distinct from all other zonesfewer native fish, more non-native species

Zone 3 very different Zones 1 and 2, not zone 4High abundance of some natives and carp

Zone 4 fish composition highly variable; greatest species richness of all zones

Valdez et al. (2001)

• Effects of a test flood on fishes of the Colorado River in Grand Canyon, Arizona. Ecological Applications 11:686-700.

• Extensive loss of beach and slackwater habitats since dam construction

• Managed flood used to rebuild these patches

• Examined response of fish

Figure 2

Why no difference infish abundance beforeand after flood?

BUT, What about other aspects of hydrology?

• Five aspects of river flow (Poff et al. 1997)

• Colorado River – predictable flood pulse, relatively low intraannual variability

• Plains rivers – greater hydrological variability

Adams et al. (2004)

• Spatial and temporal patterns in fish assemblages of upper coastal plain streams, Missississippi, USA. Hydrobiologia 528:45-61.

• Examined fish assemblages in a hydrologically variable river

Community dominated by “colonizingassemblages” – r-selected taxa

Same Pattern for Plains Rivers (Kansas R.)

• Dominant taxa– Small Cyprinidae (Notropis, Cyprinella,

Macrhybopsis, Hybognathus)– Fundulus– Other small-bodied, short-lived taxa

• Rare taxa– Piscivores– Large omnivores (e.g., Ictiobus)