The Hanford Reach is one of the few remaining unimpounded sections of the Columbia River. However, because of flow management at upstream dams, there are often large fluctuations in water level. To determine how environmental conditions might affect age-0 resident fishes in the Hanford Reach, we evaluated species composition, distribution, abundance, and standard lengths of larval and juvenile fishes along shoreline habitats during July and August 1998, 1999, and 2000. Catches in beach seine hauls during all three years were highly variable. The four most abundant taxa collected were three cyprinids, peamouth (Mylocheilus caurinus), northern pikeminnow (Plychocheilus oregonensis), and redside shiner (Richardson ius balteatus); and suckers (Catostoinus spp.). Highest overall catches were in sloughs of the Hanford Reach in 1999, a year with high flows, lower water level fluctuations, and more vegetation. Mean shoreline summer water temperatures were higher in 1998 than in 1999 and 2000, and mean lengths of the four most abundant taxa in late August were also greater in 1998, due presumably to enhanced growth or an earlier spawning season. In spite of flow fluctuations, overall catches of age-0 resident fishes were greater in the riverine Hanford Reach compared to past catches in a more lentic Columbia River reservoir. High abundances of age-0 resident fishes in the Hanford Reach could be due to more spawning and rearing habitat in this structurally complex area, and may mitigate for negative effects of variable flow regimes.
