good catches of rainbow trout, with fish ranging from .7 to 2.7 kg [Ih to 6 

 lb) being harvested by anglers. 



Stocking recomnendations for a warm-water fishery in the reservoir were 

 implemented in 1963 and are summarized in table 22. Northern pike fry and 

 fingerling were stocked from 1963 through 1966 to develop a self-sustaining 

 population. Northerns were not planted in 1967 and 1968, as a check on natural 

 reproduction, but were again planted in 1969. Finger! ings, rather than fry, 

 were planted from 1972 to 1976 to evaluate the effects of different numbers and 

 sizes of fish. Channel catfish were introduced in 1963 and 1964, and largemouth 

 bass were planted in 1964 and again in 1972 and 1973. Walleye were stocked from 

 1965 to 1969. Since the first plant of walleyes would have matured in 1970, this 

 plant was discontinued as a check on spawning success. 



SAMPLING RESULTS 



Fish were collected for analysis using the methods explained on page 83. 

 Results of frame trap net catches are tabulated by month and reservoir zone for 

 each species collected in tables 23 (1975 collections) and 24 (1976 collections). 

 As shown in table 25, the number of fish taken per net night with trap nets has 

 increased since 1972. Catch rates per net night were similar from 1972 through 

 1974 but more than doubled from 1974 to 1975 and from 1975 to 1976. Fewer traps 

 were fished in 1976, and efforts were concentrated on catching mature northern 

 pike for an egg viability study. 



Gill nets are utilized to follow fish population trends. Eighteen experi- 

 mental gill nets were fished on the bottom for a 24-hour period each year. Gill 

 net catches for the years 1964 through 1976 are summarized in table 26. Table 

 27 shows average lengths and weights, as well as number caught per net, for all 

 species collected in overnight gill net sets. 



Northern Pike 



Habitat Preference . Marshes and warm, weedy bays constitute the preferred 

 spawning habitats of northern pike (Esox Indus) in lakes and reservoirs. Spawn- 

 ing occurs in the early spring, immediately after the ice melts. Mature adults 

 move into shallow, vegetated marshes and bays for spawning, scattering their eggs 

 over the vegetation. The physical characteristics and water level management of 

 the Tongue River Reservoir has resulted in a limited amount of good northern hab- 

 itat. Marshes are present only during maximum storage; weedy bays are almost 

 nonexistent. Natural reproduction has not been documented in the reservoir. 



Catch Rates and Distribution . Frame trap nets fished during the spawning 

 season in 1975 and 1976 caught a total of 176 and 132 northern pike, respect- 

 ively (tables 23 and 24). In 1975, 29.5 percent (52 of 176) of the northerns 

 were recaptured one or more times; in 1976, 35.6 percent (47 of 132) of the sam- 

 ple were recaptured fish. 



Northern pike were taken almost exclusively in zone A in 1975 (91.5 percent 

 of the total northern catch); in 1976 the catch was distributed between zones 

 A (62.1 percent) and B (37.9 percent). Zone A represents the best northern hab- 

 itat in the reservoir. In 1975, the greatest northern catch (55.1 percent) oc- 

 curred in May. In 1976, most northerns (59.1 percent) were captured in April. 

 Spring ice melt was late in 1975 (about April 24) as compared to 1976 (April 9), 

 which accounts for the greater April catch rates in 1976. 



87 



