<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
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