Size, Age, and Growth. Northerns ranged in length from 394 to 1,156 mm 

 (15.5 to 45.5 in) in 1974, 282 to 1,301 mm (11.1 to 51.2 in) in 1975 and 571 

 to 1,165 mm (22.5 to 45.9 in) in 1976 (table 28). Average lengths were 719, 

 808, and 802 fin (28.3, 31.8, and 31.6 in), respectively, while the average 

 weight increased from 2,937 g (6.46 lb) in 1974 to 3,236 g (7.12 lb) in 1976. 

 The length-frequency distribution of northerns caught in the traps reveals 

 distinct age groups in the spawning population (figure 31). The fingerlings 

 planted in 1972 entered the spawning population in 1974 at a length interval 

 of 450-650 mm (18 to 26 in). This age class increased to a length interval of 

 500-700 mm (20 to 28 in) in 1975 and 700-850 mm (28 to 33.5 in) in 1976. The 

 reduction in the number of northerns planted in 1973 and 1974 is shown by lack 

 of distinct age groups entering the spawning population in 1975 and 1976. The 

 absence of these age groups further suggests limited natural reproduction in 

 the reservoir. 



TABLE 28. Average lengths and weights of northern pike caught in trap nets in 

 the Tongue River Reservoir, 1972-76. 



Year No. 



CONVERSIONS: 1 m\ = .0394 in 

 1 g = .0022 lb 



^Does not include recaptures. 



The average length of northern pike taken in gill nets for the years 1964- 

 1976 shows wide variation (figure 32). The increase in length from 1964 to 1969 

 represents maturity of early plants. The reduction in 1970 followed by an in- 

 crease reflects the discontinuance of stocking followed by stocking resumption. 



A small sample of scales (17) taken from trap-netted pikes were analyzed 

 for age class sizes. Three age classes (II - IV) were represented, and the 

 mean length fo"" each age class was 218 tin (four fish), 523 mm (nine) and 773 mm 

 (four), respectively. These are within the ranges reported for other northern 

 pike populations (Scott and Grossman 1973). The mean length of age group IV 

 (773) corresponds closely with the mean of the 1972 age class, as shown in 

 the length-frequency distribution (figure 32). 



Population Estimates. Population estimates were computed for northern pike 

 based on the modified Schnabel estimator using trap-netted fish. Estimates of 

 northern pike population greater than 275 mm were 272 in 1974, 228 in 1975, and 

 138 in 1976 (table 29). Confidence intervals at the 95 percent level showed a 



94 



