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<br />338 BIOLOGICAL REPoRT 19 <br /> <br />before release from the existing structure. Con- <br />struction of a submerged weir upstream from the <br />fixed outlets of these mainstem dams would cause <br />cold bottom water to mix with warmer surface <br />waters before discharge into the river down- <br />stream (Cassidy 1989). This may abate some of <br />the effect and should be relatively less expensive <br />than retrofitting the dam with a series of outlets <br />at different elevations on the dam face. If the weir <br />was constructed with quartzite rock it would also <br />serve as an underwater reef with fisheries bene- <br />fits. <br /> <br />Fish Bypass <br /> <br />Large numbers of paddlefish, blue sucker, and <br />buffalo, as well as most other native fishes, accu- <br />mulate in the tailwater of Gavins Point Dam, e-s- <br />pecially in early spring. We have sucCessfully used <br />these concentrations to acquire information about <br />the size and age structure of these fish stocks; <br />however, we have also observed breeding-sized <br />adults, fully ripe, with no hope of rmding adequate <br />reproductive substrate in the tailwater. <br />Gavins Point Dam provides a good opportunity <br />to develop a fish bypass because many fish are <br />attracted to the strong currents in the narrow <br />discharge canal downstream from the powerhouse. <br />Large numbers of fish can be seen swimming along <br />the south wall. A fish elevator could readily, be <br />installed on this wan and used in conjunction with <br />a collection and trucking facility on the bank, <br />which would not require alteration of the dam. <br />Such a facility should be cost effective, and an <br />elevator design would work effectively for most <br />native species regardless of size. These species <br />would subsequently be provided access to Lewis <br />and Clark Lake and 72 km of unchannelized Mis- <br />souri River. We recommend that the U.S. Army <br />Corps of Engineers investigate construction, of <br />such a bypass. <br /> <br />Sport and Commercial Harvest <br />Restrictions <br /> <br />Native fish stocks in the riverine portions of the <br />river in Nebraska are only a fraction of their pre- <br />vious size, a result of changes in form and function <br />of the present versus primordial Missouri River. <br />As density declined and habitat shrank, overfish- <br />ing occurred. First, the largest and oldest speci- <br />mens were eliminated, and eventually the stocks <br />were damaged (Hesse and Mestll990). With few <br /> <br /> <br />exceptions (i.e., drum, redhorse, carpsucker, <br />goldeye) most native fish stocks of the Missouri <br />River are declining, and harvest cannot be sus- <br />tained at the present level. <br />Sport and commercial fishing must not be al- <br />lowed to overharvest remaining fish stocks. Future <br />recovery depends on the maintenance of native <br />genetic stocks. The harvest of sauger, largemouth <br />bass, crappie, buffalo, blue sucker, and gar should <br />be restricted until Sur'ley data indicate that a <br />harvestable surplus can be sustained. Paddlefish, <br />shovelnose sturgeon, blue catfish, and flathead <br />catfish reproduction is not highly successful, but <br />because they are long-lived and slow-growing, they <br />seem more numerous than other stressed species. <br />Harvest of these fishes should be limited and con- <br />trolled. Paddlefish harvest has been closely man- <br />aged in recent years, and the population in Ne- <br />braska appears to respond to careful management. <br /> <br />Needed Research <br /> <br />Future research should be focused on evalu- <br />ation of implemented restoration design. The dete- <br />riorated condition of many native species indicates <br />the need for implementation of a comprehensive <br />mal1sgement plan. Much is already known about <br />Missouri River ecosystem. function; the time has <br />arrived to implement real restoration. <br /> <br />Cited Literature <br /> <br />Auer, N. A. 1982. Identification of larval fishes of the <br />Great Lakes Basin with emphasis on the Lake Michi- <br />gan Drainage. Great Lakes Fishery Commission, <br />Special Publication 82-3, Ann Arbor, Mich. <br />Bailey, R M., and M. O. Allum. 1962. Fishes of South <br />Dakota. Museum of Zoology, Miscellaneous Publica- <br />tion 119, University of Michigan, Ann Arbor. <br />Bazata, K. 1991. Nebraska stream classification study. <br />Nebraska Department of Environmental Quality, <br />Lincoln. <br />Benke, A. C., R L. Henry, III, D.M. Gillespie, and R.J. <br />Hunter. 1985. Importance of snag habitat for animal <br />production in southeastern streams. Fisheries <br />10(5):8-13. <br />Bilby, R E., and G. E. Likens. 1980. Importance of <br />organic debris dams in the structure and function of <br />stream ecosystems. Ecology 61:1107-1113. <br />Bilby, R E., and J. W. Ward. 1991. Characteristics and <br />function of large woody debris in streams draining <br />old-growth, clear-cut, and second-growth forests in <br />