98 BUXLETTN OF THE BtTKEAlT OF FISHERIES 



fish. Virtually without exception the biennial reports of the fish and game com- 

 missioners since that time have stressed the importance of fish screens. 



Two classes of fish of quite different habits are involved in the problem of fish 

 protection. They are those of anadromous habits, such as the salmon and steelhead 

 trout, and those that confine their migration entirely to fresh water. Sportsmen 

 are interested in both classes, while the commercial fishermen, especially in the West, 

 are interested almost entirely in fish that mature at sea. 



Of the anadromous fish, the various species of salmon are by far the most im- 

 portant on the Pacific coast. Their habits are such that they are particularly 

 susceptible to destruction, due to unnatural waterway conditions. Artificial stream 

 barriers prevent the mature fish, returning from the ocean, from reaching their 

 spawning beds in the headwaters of the streams. This necessitates the construc- 

 tion of fishways around or over these barriers. The young salmon fingerlings, when 

 impelled by instinct to migrate seaward, are confronted by the peril of destruction in 

 large numbers by entering irrigation ditches, canals, mill races, and other dangerous 

 watercourses. This danger can be eliminated only by the proper protection of the 

 entrances to these waterways. This is not an easy task, especially if mechanical 

 screens are used, because J^-inch mesh is required to give protection to the very 

 young fry in the yolk-sac stage. The largest salmon to which protection would 

 have to be afforded during their seaward migration would probably be the yearling 

 Chinook salmon. Dr. Willis H. Rich has found that the average length of yearling 

 chinook salmon is approximately 4 inches (100 millimeters), both in the Columbia 

 and Sacramento Rivers (Rich, 1920). It is obvious, then, that if mechanical screens 

 were constructed to protect only the yearling salmon, the mesh would be small and the 

 accumulation of leaves and debris would be a constant menace to the flow of water 

 through the screen. What is true of the screens for the protection of salmon is 

 likewise true of screens for protecting the fish hving exclusively in fresh water. Some 

 of the larger sizes of these fresh-water fish could be protected by screens of larger 

 mesh. This would make the screen slightly less susceptible to the accumulation of 

 debris. However, such screens obviously would offer only partial protection. 



PROTECTIVE LAWS 



Adequate laws have been enacted by the legislatures in all of the States having 

 this fish-protection problem. These laws give all legal authority necessary for the 

 protection of the entrances to dangerous waterways if satisfactory devices are avail- 

 able with which to screen them. A typical example of such laws is found in section 

 61 of the game laws of Oregon, quoted here: 



Any person owning, in whole or in part, or leasing, operating, or having in charge any irrigation 

 ditch, or canal, mill race, or other artificial watercourse, taliing or receiving its waters from any 

 river, creek, or lake in which fish have been placed or may exist, shall, upon order of the State game 

 commission, place or cause to be placed, and shall maintain, to the satisfaction of the State game 

 commission, over the inlet of such ditch, canal, mill race, or watercourse, a grating, screen, or other 

 device, either stationary or operated mechanically, of such construction, fineness, strength, and 

 quality as shall prevent any fish from entering such ditch, canal, mill race, or watercourse, to the 

 satisfaction of the State game commission. But before said State game commission shall adopt 

 anv permament plan for a screen or device to be placed in irrigating ditches, it shall be its duty to 

 conduct a competitive examination, and at such examination all persons desiring to do so may 



