Stocking 103 



no stock from outside sources. Fish in waters that receive 500 or more 

 hours of fishing pressure per acre per season and that escape being 

 caught are probably more wary than those that are caught. If wariness is 

 associated with an inlierited behavior pattern, it might in time become 

 incorporated in all of the fish in this population. No one lias devised a 

 means for testing this theory, but it is conceivable that an isolated large- 

 mouth bass population exposed to this type of selection for many gen- 

 erations might furnish low annual production to anglers. 



Unsuccessful Reproduction 



Control of overproduction of young fish often is one of the major 

 problems in fish management. In this respect, low production or non- 

 production of certain hybrids may be an asset. Although most fishes have 

 a high reproductive potential, as described on page 92, this potential 

 may not be realized, either because of unfavorable environmental con- 

 ditions, actual predation, or intense intraspecific competition of young. 

 Eschmeyer -^ described unusual concentrations of dead walleye eggs 

 observed in 1948 in Lake Gogebic. He was unable to determine causes 

 for the low viability of these eggs. In Fork Lake (Illinois) the produc- 

 tion of 40 bluegill nests w^as almost completely wiped out by predation 

 from stunted yearling bass.^^ Channel catfish and flathead cat usually 

 fail to reproduce in ponds. '^^ Under certain conditions this inability to 

 reproduce might be an asset, in that one could control the numbers of 

 these catfishes in ponds through stocking, which is impossible when using 

 any of the species of bullheads. 



Observations of the limiting or curtailing of fish reproduction that can 

 be traced to identifiable causes are extremely important because methods 

 may be suggested for curtailing the survival of the young of a less de- 

 sirable species while improving that of a more desirable one. 



STOCKING 



Many tests of stocking procedures have been made since 1935. How- 

 ever, the recommendations of the states and provinces throughout the 

 United States and Canada do not reveal much agreement among fisheries 

 biologists upon the kinds and numbers of fish useful for stocking new 

 waters or renovated old ones. This is due in part to dissimilarities among 

 the fish habitats of North America, to differences in the biology of certain 

 game and pan fishes in widely-separated parts of their present ranges, 

 as well as to regional variations in the popularity of certain fishes. Also, 

 some of the divergences in recommendations may be related to differences 

 in the objectives of stocking. For example, some biologists stock to 

 produce excellent but short-term angling as quickly as is possible; others 



