138 American Fisheries Society. 



thetical 10,000 out of a hypothetical potential of 30,000 made pos- 

 sible by the number of eggs hatched on the available breeding 

 grounds and remaining after other factors not shown in the chart 

 had exerted their effects. Only 10,000 survive the summer ; for, 

 although there are sufficient snails, molluscs, and insect life to 

 support 20,000 fingerlings to the summer's end, the supply of 

 forage fish is so scarce that the hostile fishes, inclusive of the 

 older bass, prey upon the fingerlings to this extent. 



Assuming that in this particular case it is possible to double 

 the available breeding areas by spreading gravel of the right sort 

 at proper depths, or by raising or lowering the water level, this 

 will give a potential (State B) of 60,000 fingerling bass within a 

 year or two as excess breeders take up space and more fish arrive 

 at maturity. However, as new species of vegetation, molluscs, 

 and forage fish superior to those native to the locality have just 

 been introduced, the change is not appreciable the first year fol- 

 lowing; and while an increase in the number of potential finger- 

 lings is available from the increased number of eggs hatched, the 

 hostile fishes consume the surplus nearly down to the old num- 

 ber of 10,000. 



State C, however, shows decided improvement. The number 

 of fingerlings made possible by the increased breeding areas is 

 now at its maximum of 60,000. The superior species of vegeta- 

 tion which have been introduced are taking hold well and show 

 improvement which is further evidenced by the great increase 

 among the newly introduced forage fish. The latter, however, 

 have kept the snails, molluscs and insect life retarded, though 

 on the other hand they have forced the hostile fishes to slacken 

 in their persecution of the bass fingerlings, over 20,000 of which 

 survive the summer. 



