A NATIONAL PLAN FOR AMERICAN FORESTRY 519 



last analysis this is the most important factor in determining the 

 number of fish which a body of water will support. It is also true 

 that in many streams it is a comparatively simple matter to increase 

 the amount of available food. Logs, boulders, and gravel greatly 

 increase the hard stratum over which insects may crawl and also serve 

 as a support for an abundant growth of algae on which they feed. 

 Weed beds, especially of the submerged type, provide very favorable 

 conditions for the growth of food organisms. Comparatively little is 

 known, however, of the conditions which will promote the growth of 

 many plants and animals utilized as food and much remains to be 

 done before we will be in position fully to utilize the food-producing 

 capacity of natural waters. 



Shelter and food should be considered in relation to one another 

 since most shelter devices tend to increase the supply of food. The 

 functions of shelter are primarily for protection, but in fast-flowing 

 streams such devices may slacken the current so that the fish may 

 rest. It also appears that sections of streams or lakes where ade- 

 quate shelter is present are more attractive to fish. Conversely many 

 sections of streams or lake margins are practically free of fish owing 

 to the absence of shelter. It has been shown recently in the case of 

 Michigan trout streams that long stretches of heretofore troutless 

 waters can be made to yield good catches of adult fish by the installa- 

 tion of proper shelter devices. 



Shelter may be provided in many forms and degrees. Almost any 

 obstruction in the water gives some shelter and a few twigs or pebbles 

 may suffice for small fish. In streams shelter can best be provided in 

 connection with pools. Logs and boulders are soon undermined by 

 the combined action of fish and current and furnish excellent places for 

 the fish to hide. Weed beds also provide excellent shelter, especially 

 for young fish. Deflectors or dams so constructed as to cause the 

 stream to undercut its banks are very effective. 



A prime requisite for a permanent fish population is the provision 

 of adequate spawning facilities. These, of course, will take different 

 forms according to the species of fish concerned. In the case of trout, 

 gravel beds in spring-fed streams are required, and the lack of such 

 beds is not infrequently a limiting factor. In some instances such 

 beds can be provided by the installation of deflectors which will cause 

 the current to sweep away silt or sand covering old gravel deposits. 

 In other cases it may be necessary to haul gravel for this purpose. 

 Small-mouth bass also require gravel beds near the lake shore or in the 

 bed of streams while large-mouth bass spawn on mud bottoms where the 

 roots of plants can be easily exposed by the fanning action of the fins. 



Pollution is usually not an important factor in forested areas, but 

 in some cases sawdust or refuse from mining operations may cause 

 considerable damage. Their effect is much the same as that of silt, 

 being especially destructive to the eggs of fish and to their food. 



MEANS OF CARRYING INTO EFFECT A PROGRAM OF FISHERY 

 MANAGEMENT IN THE FOREST AREAS 



AGENCIES CONCERNED 



There are many agencies concerned with the propagation, dis- 

 tribution, stocking, utilization, and management of the fishery 

 resources of the United States. These include various branches of the 



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