Many studies have assessed the effects of large dams on fishes and macroinvertebrates, but few have examined the effects of lowhead dams. We sampled fishes, macroinvertebrates, habitat, and physicochemistry monthly from November 2000 to October 2001 at eight gravel bar sites centered around two lowhead dams on the Neosho River, Kansas. Sites included a reference site and a treatment site both upstream and downstream from each dam. Multivariate analysis of variance indicated that habitat, but not physicochemistry, varied immediately upstream and downstream from the dams, with resultant effects on macroinvertebrate and fish assemblages. Compared with reference sites, upstream treatment sites were deeper and had lower velocities and downstream treatment sites were shallower and had higher velocities; both upstream and downstream treatment sites had greater substrate compaction than reference sites. Macroinvertebrate richness did not differ among site types, but abundance was lowest at downstream treatment sites and evenness was lowest at upstream treatment sites. Fish species richness did not differ among site types, but abundance was highest at downstream reference sites and evenness was highest at upstream sites. The abundance of some benthic fishes was influenced by the dams, including that of the Neosho madtom Noturus placidus, which was lowest immediately upstream and downstream from dams, and those of the suckermouth minnow Phenacobius mirabilis, orangethroat darter Etheostoma spectabile, and slenderhead darter Percina phoxocephala, which were highest in downstream treatment sites. Although limited to one system during a 1‐year period, this study suggests that the effects of lowhead dams on fishes, macroinvertebrates, and habitat are similar to those reported for larger dams, providing important considerations for riverine ecosystem conservation efforts.

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A large, multiyear (1981-1986) gillnetting data set was used to assess patterns of seasonal habitat use by striped bass Morone saxatilis in Lake Texoma, Oklahoma-Texas. Large (>2.27 kg), medium (1.36-2.27 kg), and small (< 1.36 kg but not including age-0 individuals) fish exhibited different patterns of seasonal abundance in a study area about 40 km uplake from the dam. Large fish were never taken in the study area in June, July, August, or September, or when surface water temperatures exceeded 22°C. Abundance of medium-sized fish was significantly lower during June-September and when temperatures were above 22°C than in other months and at cooler temperatures. Small fish remained abundant in the uplake area all year but were almost never collected at dissolved oxygen concentrations less than 6.0 mg/L in summer. Substantial numbers of small fish were collected at temperatures as high as 29°C, but their catch per unit effort dropped from a mean of 11.8/net at 28°C to l.9/net at 30°C. Our results supported the thermal niche hypothesis for striped bass, and the response of small striped bass to high temperatures was similar to that reported previously.