Annual growth increments were calculated for blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) from the lower Mississippi River (LMR) to assess hypothesized relationships between fish growth and floodplain inundation as predicted by the Flood-Pulse Concept. Variation in catfish growth increment was high for all age classes of both species, and growth increments were not consistently related to various measures of floodplain inundation. However, relationships became stronger, and usually direct, when water temperature was integrated with area and duration of floodplain inundation. Relationships were significant for four of six age classes for blue catfish, a species known to utilize floodplain habitats. Though similar in direction, relationships were weaker for flathead catfish, which is considered a more riverine species. Our results indicate the Flood-Pulse Concept applies more strongly to temperate floodplain-river ecosystems when thermal aspects of flood pulses are considered. We recommend that future management of the LMR should consider ways to 'recouple' the annual flood and thermal cycles. An adaptive management approach will allow further determination of important processes affecting fisheries production in the LMR.

Gear comparison studies are useful to fisheries managers because many aquatic systems require multiple gears to assess fish assemblages. Many previous studies have emphasized comparisons of catch per unit effort or basic community measures such as richness and diversity. Our objectives were to (1) compare fish assemblage richness, diversity, and evenness across sampling gears, (2) assess the similarity of fish assemblage structure as depicted by the different gears, and (3) compare fish assemblage–environment relationships depicted by the different gears. Assessments were conducted in littoral‐zone areas of 16 floodplain lakes in the lower White River, Arkansas. Four sampling gears were used: 500‐V, 60‐Hz (high‐pulse) and 1,000‐V, 15‐Hz (low‐pulse) boat‐mounted nighttime electrofishing, mini‐fyke nets, and experimental gill nets. Species richness and diversity were significantly greater using boat‐mounted electrofishing (both pulses) than the other gears. Experimental gill nets exhibited the lowest richness of all gears (<50% of the other gears), and mini‐fyke nets exhibited significantly lower evenness owing to the tendency for 1–2 species to dominate catches. Procrustean analyses indicated that the lake‐specific fish assemblages depicted by the different gears were significantly different during all paired‐gear comparisons except between the two electrofishing configurations. Regardless of gear, multivariate direct gradient analyses indicated that lake depth, water clarity, and morphoedaphic index were consistently important variables associated with the structuring of littoral‐zone fish assemblages. The results support the idea that multiple‐gear approaches are useful in assessing floodplain lake fish assemblages and that, in the case of lower White River floodplain lakes, the assemblage information collected from the different gears was not redundant. Additionally, if a large‐river sampling program is using only one or two gears, major fish–environment relationships that are depicted may not be gear dependent.

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Floodplain lakes of large river systems contain fish habitats that are not found elsewhere within the river, and these lakes have a diversity of environmental conditions that vary in space and time. Our objective was to examine relationships between floodplain lake fish communities and environmental variables associated with lake morphology, water chemistry, and river‐floodplain connectivity in a large river‐floodplain ecosystem. Multivariate direct‐gradient analyses indicated that lake surface area, lake depth, water clarity, and (to a lesser extent) dissolved oxygen were the most important factors in the structuring of lake fish communities. Results further suggested that floodplain lakes could be placed into groups that contained distinctive fish communities. Fish community structure was not strongly related to river‐floodplain connectivity, though fish species richness in individual lakes was positively correlated with degree of flooding in those lakes. Fish species diversity in lakes was positively correlated with linear distance between lakes and the main river channel; lakes that were furthest from the main river channel had more diverse fish communities. The diversity of environmental conditions in floodplain lakes is essential for maintaining net ecosystem diversity in large river ecosystems.