sisting of 3-year old fish. During Period IX only about 11 percent of 

 the catch of these three age groups consisted of Ii and 5-year old fish. 



As a check on the effects of removing fish from the area by netting, 

 a trap net was set in Broken Arrow Slough during Period IX. This area 

 had not been netted before. This net took black crappies of approximately 

 the same length-distribution during Period IX as did the other nets which 

 had been fished all summer at the permanent netting stations. This obser- 

 vation indicates that removal of the fish from the waters around the 

 netting stations probably did not significantly affect changes in length- 

 frequency of the catcho 



It is also possible that migration influenced the catches during the 

 season. However, buffalo nets set in the main channel caught only an 

 occasional crappie during the study. Their mesh was small enough to take 

 black crappies over 9oO inches long. It appears that any losses from the 

 population due to migration are small and that the principal cause of 

 losses was natural mortality. 



3. Activity of the Black Crappie . 



Two catch fluctuations noted during the season .can best be attributed 

 to changes in rate of activity of the fish. They are (1) the marked drop 

 in catch rate that occurred between Periods I and II when only the 

 "residual" population was present and (2) the great increase in catch 

 rate observed in late August and September after most of the recruitment 

 to the popiolation had occiirred, A small drop in catch rate was also 

 noted between Periods V and VI , that may also be related to a change in 

 rate of movement. 



Some changes in activity rate are probably related to changes in 

 environmental conditions. It will be noted from Figure 5 which shows 

 water levels and water temperatures, that the decrease in catch in June 

 was coincidental with the stablization of water levels. There was a 

 drop in water levels of 1.6 feet during Period I and by the beginriing of 

 Period II, the water levels had dropped another 0,6 foot. After the 

 beginning of Period 11^ the water level remained within 0.2 feet of nor- 

 mal pool stage for the rest of the season. It is generally believed by 

 eomiriercial fishermen who fish t he area that water level fluctuations affect 

 fish movement o 



Water temperature is also known to affect fish movement and behavior 

 patterns (Fry and Hartj I9I43) . Means of temperatures taken one foot below 

 the surface of the water each day at each netting station are shown in 

 Figure L.. Catch of black crappies was highest when the water temperature 

 was between 6o* and 70* F.| that is during the spring and fall. Fluctua- 

 tions of water temperatures above 70° F., seemed to have no consistent 

 effect on the catch. 



13 



