(median elapsed time) -' required by the 

 fish to negotiate the fishway was less under 

 the dark thcin under the light condition. 



The slower median entry time at weir 

 54 under the dark condition can be at least 

 partially explained by the fact that the 

 fish were observed to hesitate more before 

 passing through the small entrance gate (10 

 inches wide) in the dark condition than in 

 the light. 



Table 1 lists the median elapsed times 

 for the four control and four test trials. 

 The average median elapsed time under the 

 dark condition was 2.0 minutes and the aver- 

 age median elapsed time under the light con- 

 dition was 8.5 minutes. A "t" test indi- 

 cates that passage through the fishway was 

 significantly faster in the dark condition. 



Tcible 1. — Summary of light and dark fishway 

 trials showing effect of lighting condi- 

 tion upon passage time. 



The degree to which the results of 

 this limited experiment may be safely ap- 

 plied is a matter of conjecture. Additional 

 experiments are necessary to determine the 

 relationship between fishway dimension and 

 design and the degree to which the behavior 

 of salmonoids is affected by low light in- 

 tensities. As the present experiment applies 

 almost exclusively to steelhead, it will be 

 of interest to examine the behavior of other 

 salmonoids under similar test conditions. 



£/ The mediein elapsed time is defined as 

 the difference between the median entry 

 (at weir 54) and median exit (at weir 

 60) time. 



SUMMARY 



The experiment was designed to deter- 

 mine the effect of low light intensities 

 upon the rate of passage of adult migrating 

 salmonoids through a pool-and-overf all-type 

 fishway without submerged orifices. The 

 fishway, 4 feet wide by 96 feet long, con- 

 sisted of six 16-foot pools with a 1-foot 

 rise between pools. Average water depth in 

 the pools was 6.3 feet and the head on each 

 weir was 0.8 foot. 



The fishway was darkened for four test 

 trials aind lighted for four control trials. 

 A total of 82 steelhead and 1 chinook were 

 passed through the darkened fishway and 100 

 steelhead and 3 chinook through the lighted 

 fishway. Light measurements taken during 

 the dark condition yielded values between 

 0.1 foot candle downstream of the fishway 

 and near-total darkness in the central por- 

 tion of the fishway. Light readings taken 

 at the surface of the fishway pools during 

 the lighted condition yielded values ranging 

 from 300 to 1000 foot candles. 



The average mediaui elapsed passage 

 time through the dark fishway was 2.0 min- 

 utes and through the light fishway 8.5 

 minutes. A significantly faster rate of 

 passage through the dark fishway is indi- 

 cated. 



ACKNOWLEDGMENT 



Personnel participating in the experi- 

 ment included Dr. Gerald B. Collins, Carl 

 H. Elling, Joseph R. Gauley, Charles R. 

 Weaver, Clark S. Thompson, Robert J. Hol- 

 corab, James S. Johnson, and D. Lee Ellison. 

 The manuscript was reviewed and suggestions 

 were offered by the Biometrics Unit of the 

 Pacific Salmon Investigations and Milo C. 

 Bell. The author gratefully acknowledges 

 this assistance. 



LITERATURE CITED 



S. ARMY, CORPS OF ENGINEERS 



1948 Passage of fish over Bonneville 

 Dam, Columbia River, Oregon and 

 Washington. Ann. Rep. Corps of 

 Engineers, U. S. Army, Office of 

 the District Engineer, Portland, 

 Oregon. 21 p. 



