of the dominant species in the reservoir, but 

 individuals will be slow growing and small. 



CHANGES IN GROWTH 



Comparison of the average length attained 

 by fishes of the same age collected from 1956 to 

 1962 indicated that fish growth rate has decreas- 

 ed since impoundment. This is illustrated for 

 carp, river carpsucker, white crappie, and 

 sauger in figures 2 through 5. The sharpest 

 growth change was evident for the carp, especial- 

 ly after the first year of life. There was a gen- 

 eral but less severe decrease in growth for all 

 ages of river carpsucker. Decrease in growth 

 of white crappie was most evident for fish over 

 3 years of age. Sauger growth, except for age 

 I fish, appeared least influenced by impoundment. 



There was no apparent relation between 

 changes in relative abundance and growth of river 

 carpsucker and white crappie between 1956 and 

 1962 . Abundance of river carpsucker remained 

 relatively unchanged (table 6) while its growth 

 rate decreased (fig. 3). Abundance of white 

 crappie first increased and then decreased 

 (table 6) while its growth rate decreased (fig. 4). 

 Both relative abundance and growth rate of carp 

 decreased sharply from 1956 to 1962 (table 6; 

 fig. 2). Relative abundance of sauger (table 6) 

 increased while its growth rate declined (fig. 5) 

 over these years. The significance of these 

 relationships is unknown at present. Decrease 

 in fish growth since impoundment was probably 

 caused by a change in tlic aquatic environment 

 independent of the relative abundance of the 

 individual fish species . 



DISCUSSION 



Studies in Lewis and Clark Lake from 1956 

 to 1962 indicated that the reservoir was domi- 

 nated by carp, river carpsucker, and white 

 crappie, with relatively few game and pan fishes. 

 Relative fish abundance, as determined by exper- 

 imental gill net and frame net catches, generally 

 decreased after 1957, with a greater proportion- 

 ate decrease in sport fish than rough fish 

 numbers . Fish reproduction and growth were 

 generally good for all species during the first 

 year of impoundment, but were poor for most 



Figure 2: --Growth history of carp in Lewis and 

 Clark Lake during the first 7 years of impound- 

 ment. Solid lines connect points representing 

 average lengths of age groups (Roman numerals) 

 at time of capture (June -August). Number of 

 fish aged in parenthesis . 



Figure 3:--Grovvth history of river carpsucker 

 in Lewis and Clark Lake during the first 7 years 

 of impoundment. Solid lines connect points rep- 

 resenting average lengths of age groups (Roman 

 numerals) at time of capture (June -August). 

 Number of fish aged in parenthesis. 



22 



