9.0 percent in those years. Catch rates for white crappie have increased from 

 1.99 fish per trap night in 1972 to 85.15 fish per trap night in 1976 (table 

 25). Black crappie have also increased since 1972, but not as dramatically. 

 In 1975, both species were taken in greatest numbers during June, with 81.3 per- 

 cent of the whites and 60.1 percent of the blacks taken that month. In 1976, 

 83.7 percent of the whites and 75.0 percent of the blacks were caught during 

 May. 



White crappie were the predominant species in gill-net catches in 1975 

 and 1976 (table 27). Blacks were represented in the gill nets at about the 

 same levels as in trap nets (table 25). White crappie sample size almost 

 doubled from 1975 to 1976 (265 to 465), resulting in a corresponding increase 

 in the spring population estimate. The average size of white crappie was simi- 

 lar in 1975 and 1976. 



Crappie exhibited a differential distribution pattern in the reservoir. 

 In 1975, 59 percent of the blacks were taken in zone C, while only 7.8 percent 

 of the whites were captured in that zone. Zone B produced the majority of the 

 white crappie in 1975 (77.4 percent). The 1976 results are masked somewhat, 

 since traps were not fished in zone C equally as in zones A and B. Still, 

 white crappie were found almost exclusively in zones A and B (97.4 percent), 

 while blacks were distributed more evenly; Zone C produced 25.2 percent of the 

 blacks. Catch rates in zones A, B, and C in 1976 for white crappie were 104.6, 

 102.6, and 11.1 fish per net night respectively, as compared to 9.6, 8.7, and 

 12.3 fish per net night, respectively, for black crappie. The distribution 

 pattern probably reflects a difference in water quality between the upper (zone 

 A) and lower (zone C) ends of the reservoir. The difference in distribution 

 reflects the habitat preferences of each species, with blacks preferring clearer 

 water (Brown 1971). 



Size, Age, and Growth . Length-frequency distribution for black and white 

 crappie for 1975 and 1976 trap-net catches is shown in figure 35. Black crappie 

 show a greater distribution of lengths, ranging from under 100 to 499 mm (3.9 

 to 19.6 in), while white crappie ranged from 100 to 399 mm (3.9 to 15.7 in). 

 Black crappie produce larger fish, with specimens to 1,362 g (3 lb) common. In 

 both years, the modal size for whites was 225 mm (8.9 in), compared with 250 mm 

 (9.8 in) for blacks. 



Scales taken during the spring (April-May) 1975 trap net season from black 

 and white crappie were analyzed for age and growth. A summary of lengths and 

 masses is shown in table 33. The oldest white crappie taken were of age group 

 X; the oldest black crappie were of age group VIII. White crappie grew faster 

 until age V, at which time the blacks took over. By weight, blacks caught up 

 with whites at age IV. A comparison of lengths of fish taken in June and July 

 shows a faster growth rate for blacks than whites. Comparing the age data with 

 figure 35, age III fish contribute the greatest percentage of the spawning pop- 

 ulation. A comparison of age data on black and white crappie with data from 

 other northern waters (Nelson 1974, Scott and Grossman 1973) shows that the 

 fish in the Tongue River Reservoir grow at similar rates. 



Population Estimates . Population strengths of black and white crappie 

 were estimated in 1975 and 1976 (table 34). The total crappie estimate in 

 1975 was 46,613 fish, with whites contributing 94.6 percent of the total. 

 The population increased in 1976, with a total estimate of 95,684 crappie 



101 



