Longitudinal distribution of fish in the Tongue River is influenced by 

 irrigation diversion structures. The T & Y Diversion is the upstream limit 

 for goldeye, walleye, burbot, paddlefish, shovelnose sturgeon, blue suckers, 

 and sturgeon chubs. Channel catfish did not occur above the Brewster Diversion. 

 Flathead chubs are found upstream from the Mobley Diversion, but in limited 

 numbers when compared to dovmstream sections. 



Distributional patterns changed in 1975. Extensive high water during 

 the spring and summer resulted in damage to Mobley's and Brewster's diversions, 

 allowing fish passage. Five species (mountain sucker, yellow bullhead, 

 pumpkinseed, smallmouth bass, and black crappie) which had not previously been 

 found above Brewster's diversion were found in section Vc in 1975. 



POPULATION NUMBERS AND SPECIES COMPOSITION 



A comparison of the 1974 and 1975 electrofishing results is shown in 

 table 3. Fish captured per trip expressed as numbers/km were similar between 

 the two years. The number of species decreased in sections lb and lib 

 and increased in sections IVb and Vc. In all cases, gains or losses were of 

 rare species. Section Vc showed the greatest change in both number of fish 

 (which increased from 231 to 292) and number of species (which increased 

 from n to 15). In the same section, sucker composition changed from short- 

 head redhorse dominance to longnose sucker dominance, and white suckers 

 showed a great increase. 



Game fish concentrations were heaviest in section IVb where they made 

 up 12.7 percent of the total number; the dominant game fish was smallmouth 

 bass, which ranged in length from 53 to 342 mm (2.1 to 13.5 in). The pre- 

 ponderance of young-of-the-year fish indicates that smallmouth bass are 

 successfully reproducing. They were also found downstream from the S-H 

 Diversion, but the greatest concentration was near Birney. 



Scales taken from smallmouth bass collected in section IVb were used to 

 evaluate age-class strengths for 1974, 1975, and 1976. The distribution of 

 age classes through IV is shown in table 4. Age smallmouth bass contri- 

 buted 37.3, 7.3, and 73.3 percent of the total smallmouth sample in 1974, 

 1975, and 1976, respectively. The low reproductive success of bass in 1975 

 is reflected in the number of age class I fish collected in 1976. High 

 discharges from the Tongue River Dam during the spring and summer of 1975 in 

 preparation for repairs to the dam apparently reduced smallmouth reproduction. 

 Reynolds (1965) suggested that water levels might be more important than 

 temperatures in initiating spawning of smallmouth bass in tributaries of the 

 Des Moines River, Iowa. In Courtois Creek, Missouri, smallmouth bass nesting 

 always began during a period of stable or gradually declining water levels 

 and was delayed or interrupted some years by floods (Pflieger 1975). Stable 

 flows during the spawning and incubation periods were considered more 

 important for successful smallmouth bass reproduction than a specific flow 

 level (White and Cochnauer 1975). This philosophy was strongly considered 

 when developing the minimum flow recommendations for the Tongue River dis- 

 cussed below under "Impacts of Water Withdrawals." 



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