132 Theories and Techniques of Management 



tions of 1957 showed very large numbers of 1956 year-class fish that, 

 after two growing seasons, were only about 3.0 inches in length. This 

 would indicate a dangerous situation that might mark the beginning 

 of overpopulation and stunting of bluegills. Further evidence of popula- 

 tion pressure in 1957 was found among the 1954 and 1953 year-class blue- 

 gills which had Indexes of Condition of 7.0 and 7.4 respectively, indicating 

 that the larger fish were thinner in 1957 than in previous years. 



Table 6.1 Length-frequency distribution of bluegills 



IN clear lake from SEPTEMBER COLLECTIONS 

 TAKEN WITH WIRE TRAP NETS. 



By September of 1958, the 1956 year class was severely stunted. After 

 three growing seasons ( summers ) they averaged only 4.0 inches in length 

 and were thin with abnormally large eyes (an indication of stunting). 

 Bluegills of 6 inches or larger were still fairly common, but were very 

 thin with Indexes of Condition ranging from 6.5 to 6.9. This bluegill 

 population needed to be drastically reduced, particularly those fish be- 

 longing to the 1956 year class. Furthermore, since the 1957 sampling dis- 

 closed an abnormally large 1956 year class, measures should have been 

 taken then to reduce its size. 



Sampling Methods 



Many types of gear have been used for sampling populations. Most of 

 these are selective for one or more kinds of fish, and may give a faulty 

 impression of the relative abundance of species— both those too easily 

 caught and those not taken in proportion to their numbers. 



Table 6.2 gives a rough appraisal of the efficiency of several kinds of 

 sampling methods in relation to a number of kinds of warm-water fishes. 



