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sunfish, despite thousands having been removed, suggests that: (1) the number removed may have been insignificant compared to the total number present, or that (2) centrarchid populations were resilient and capable of quickly replacing those removed through reproduction and/or immigration. The relative effects of immigration, emigration, reproduction and mortality on backwater populations of centrarchids remains unknown. Although many backwaters were isolated or semi-isolated from the main channel during base flow (due to below- average flow conditions), connection to the main channel was generally made during spring runoff when they were either inundated at the mouth or became flow-through channels. During these times, numbers of fish in the backwater could potentially increase or decrease if there was a net movement of fish in or out of the backwater. However, between fall and the following spring, isolation of many backwaters precluded ingress and egress; hence, fish collected in early spring prior to runoff were assumed to be those missed during the previous fall removal effort. The exception to this would be in those backwaters that had irrigation returns draining directly into them; in this situation, the possibility existed for fish numbers to be augmented from off-river sources between fall and spring efforts. Hence, immigration and emigration, though never documented, was possible in most backwaters in most years. During fall 2001, it appeared that some isolated backwaters, because of low runoff conditions, had not become connected to the main channel in spring as in previous years. During this time, reproduction was documented, based on length-frequency analysis, within two backwaters: largemouth bass reproduction in Horsethief backwater and green sunfish reproduction in Pumpkin- Head backwater (see Results above). Natural mortality was difficult to recognize as separate from removal mortality. For largemouth bass, there was a consistent reach- wide decline in catch rate from fall to spring (Fig. 3); this likely reflected fall removal effects, but may also have resulted from overwinter mortality. Relative abundance of YOY Colorado pikeminnow, as measured by ISMP seining catch rates, did not increase during the project period, and hence, the ultimate objective of the project was not achieved. This is an expected result given that centrarchid catch rates apparently did not decline and therefore no decrease in potential 21