<em>Abstract</em>.—We examined spatial distribution of blue catfish <em>Ictalurus furcatus</em>, channel catfish <em>I. punctatus</em>, and flathead catfish<em> Pylodictis olivaris</em> at macro-, meso-, and microscales in the unimpounded Mississippi River between its mouth and the mouth of the Missouri River (river kilometer 1,847). Fish collections represented 1,309 trotlines fished at 154 river segments in 1997–2009. Blue catfish was the most abundant catfish species, followed by channel catfi sh and flathead catfish. At the macroscale level, we tested for longitudinal gradients along five a priori reaches ranging in length from 154 to 595 km. Blue catfish and flathead catfish generally decreased in upriver reaches, whereas channel catfish were abundant at the two extremes of the river span and least abundant in middle reaches. Species catch rates at the mesoscale level varied across nine habitat types with catch rates of blue catfi sh highest along natural banks; channel catfish highest in dikes, main channel edge, and gravel bars; and flathead catfish highest in articulated concrete mattresses/riprap and steep sand bars. Percentage contribution to variance in catch rate apportioned by each spatial scale differed across species but was always highest at the macroscale level, indicating greater spatial dependence at this scale. Site-specific mesoscale and microscale conditions account for local variability in abundances and are important in allocating effort in sampling programs. However, considering macroscale has the greatest influence over catfish populations, it is at this broad-scale level that management may be most effective.
