24 Technical Paper 56: Bureau of Sport Fisheries and Wildlife

and possibly flathead catfish have increased; walleye, and sauger was faster than in Oahe the abundance of most other species for which Reservoir. Growth estimates in Oahe Reser­ we have reliable data has declined. A similar voir were based only on the early years of change has occurred in Oahe Reservoir, where impoundment, when growth rates are generally catfish, white bass, and walleye populations the highest. have increased (Higham, 1968). The following species, though most were never present in Growth of northern pike, river carpsucker, large numbers, have become rare in Lake largemouth bass, walleye, and sauger was Francis Case since the first years of impound­ better than in most other waters in this latitude ment: flathead chub, stonecat, black bullhead, in the United States, but carp and drum growth largemouth bass, green sunfish, orangespotted was poorer. sunfish, and bluegill.

The sport-fishing catch rate in Lake Francis The main forage species in the reservoir Case declined from 1954 to 1960, although the were gizzard shad, emerald shiner, and yellow catch rates for sauger and crappie increased perch. These species did not appear to be during that period. present in large enough numbers to provide an abundant forage fish population as reported The sauger population declined between in many lakes or reservoirs with shad and 1956 and 1962, while the walleye population yellow perch. As Selgeby (1968) suggests, the increased from 1959 to 1962 (fig. 8). By 1967 high zooplankton standing crop and the com­ the sauger population, which was previously paratively large individual size of the larger than that of walleye, had become the cladocerans may indicate an open niche in the smaller of the two. Sauger were more abundant fish community. Echo sounding and midwater than walleye in the turbid Missouri River trawling in 1968 showed that the large limnetic before and after its impoundment (Bailey and zone contained few fish. Yet the good growth Allum, 1962) and they remain the dominant of of piscivorous fish would seem to indicate the two species in the more turbid Lewis and that the amount of forage fish per predator Clark Lake. Sauger are known to be more was not critical. tolerant of turbid water than walleye (Trautman, 1957). The increase in walleye appears to be Of the 13 species for which preimpoundment related to the decreased turbidity of the water growth estimates are available, growth in­ following impoundment and the development of creased after impoundment for all except rubble shorelines suitable for spawning. possibly bigmouth buffalo. Growth subsequently declined back to preimpoundment levels during Growth the period from 1955 to 1959, but since about 1961-63 or 10 years after impoundment a Growth of river carpsucker, smallmouth and tendency toward increased growth was again bigmouth buffalo, carp, and white and black crap­ noted (figs. 4-7). pie was greater in Lake Francis Case than in Lewis and Clark Lake. First-year growth of white bass was probably greater in Lake Francis Reproduction Case, but growth in later years of life was greater in Lewis and Clark. The opposite was Age composition (appendixes B-Q) and probably true for channel catfish until 1962, after seining data (table 2) indicate that reproduction which growth increased in Lewis and Clark Lake. was very successful in 1953 and/or 1954, the first 2 years after impoundment, for gizzard Growth of sauger and drum was similar in shad, goldeye, northern pike, most catostomids, both reservoirs. carp, most centrarchids, sauger, and drum. Growth of bigmouth buffalo, yellow perch, Reproduction was unusually high for many and drum was equivalent to growth in Oahe species in 1967, a year of high water levels Reservoir, another main stem impoundment (1,367 feet, or 417 m, above mean sea level on on the Missouri River, but growth of carp, June 22). High spring and summer water levels