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and have only begun to analyze more than 50,500 individual records. Before 1991 only one blue cat- fish had been collected. However, in 1991, 15 young-of-the-year blue catfish were captured in total from three locations along the Missouri River in Nebraska south of Omaha. In Missouri's sec- tion, 63,191 catfish were sampled between 1980 and 1992; 1,350 (201&) were blue catfish. However, Missouri commercial fishers reported taking 37,983 kg of blue catfish, which is 27% of all catfish harvested during 1991 from the Missouri River in Missouri. We recommend that blue cat- fish be listed as endangered in Nebraska. Other Species of Special Concern Other species of special concern in Nebraska include lake sturgeon, which has probably been extirpated from Nebraska as a wild population; pallid sturgeon, which has been listed as a nation- ally endangered species and is very rare in Ne- braska; shovelnose sturgeon (Srophirhynchus platorynchus), which is declining throughout Ne- braska's portion of the Missouri River; paddlefish, which is stable to declining in Nebraska (Hesse and Mestl 1992); longnose gar (Lepisosteus osseus), which is declining and becoming uncom- mon in Nebraska; shortnose gar (L. platostomus), which seems stable, but whose primary habitats have been eliminated; blue sucker, which seems to be stable in Nebraska, but is reduced through- out its range nationwide and is a candidate for national listing; and flathead catfish (Pylodictis olivaris), which has been reduced to fewer than 1,000 individuals in the unchannelized Missouri River upstream from Lewis and Clark Lake (Hesse and MestI1991). In the following discussion we outline the rea- sons for the decline of these native fish species, and recommend remedial actions. Discussion of Cause and Effect Factors STUJ,g Removal Bilby and Ward (1991) reviewed available lit- erature on the role played by large woody debris in stream ecology. Snags were reported to alter channel morphology by influencing sediment routing, thus creating pools, gravel bars, and de- positional sites. These, in turn, reduced the rate LARRY W. HEsSE gr AI.. 335 of downstream transport of particulate material. Bilby and Likens (1980) suggested that a large part of stream organic matter is associated with woody debris. Benke et al. (1985)-.determined that inverte- brate diversity, standing stock biomass, and pro- duction per unit of surface area were much higher on snag habitat in the Satilla River, Georgia, than in the other two main habitats (shifting sandbars of the main channel and muddy depositional areas of backwaters). They reported that snag habitat contained 60% of total invertebrate biomass per unit length of river, even though snags composed only 4% of available habitat. The Satilla was heav- ily snagged in the 1940's. Steam-powered snag boats began removal of snags from the Missouri River in 1838, when 2,245 large trees were removed from the river channel and 1,700 overhanging trees were cut from the bank in the first 620 km of river upstream from St. Louis, Missouri (Chittenden 1962). Before 1885, however, snag removal was somewhat random. and extended only a few hundred kilometers up the Missouri River, although the number and tonnage of snags removed were immense (Suter 1877). After 1885, snagging intensified and became systematic. In 1901, snag boats removed 17,676 snags, 69 drift piles, and 6,073 overhanging trees in 866 km of river (Funk and Robinson 1974). Today, even un- channelized sections have few remAining snags. Leaf abscission in fall contributed a pulse of organic matter to the river system, but leaves are 90% decomposed within 1 year (Risser et al. 1981). Conversely, large woody debris provided long-term. supplies of orgaDic matter, requiring 75 years for 95% decomposition in some instances (Melillo et al. 1983). Trees of all types and sizes were essential as aquatic insect substrate, and they provided local- ized zones -of reduced velocity for fish. Snags re- duced mean stream velocity, increased the stream top width, provided long-term. organic matter sup- plies, and aided in fine organic matter retention (Benke et al. 1985; Hesse et al. 1988). Sn.ag removal from the Missouri River was completed nearly 40 years ago, but dam construc- tion eliminated large floods, and human encroach- ment on the floodplain stabilized the banks even along the unchannelized remnants. Few new snags have been introduced since 1954, when Gavins Point Dam was closed. In 1963, 68.90/0 of secondary production in the unchannelized reach in Nebraska was from ~ag habitat, while mud