EXPERIMENTAL COMPLICATIONS 



The idea of delay is simple to graps, 

 but delay defined as above is hard to mea- 

 sure. What, exactly, do we mean by "average 

 number present"? The computed average time 

 necessarily applies to all fish passing in 

 the entire test interval. However, the 

 relationship of figure 1, derived from a 

 series of tests, is of most interest during 

 a central portion of the test interval when 

 the "average number present" is at a maxi- 

 mum. The number present, of course, fluctu- 

 ates widely over the entire interval. But 

 if one were to average the numbers present 

 at successive time units in the center of a 

 test interval, as between time units 2 and 

 4 in figure 2 when entry and exit rates are 

 sustained, he would both satisfy the require- 

 ment of figure 1 and reduce the variation 

 around the average number present. 



We may visualize, from figure 2a, a 

 large number of test fish available for 

 entry into an experimental fishway contain- 

 ing no fish. The available fish begin to 

 enter at time-unit 0, then maintain a quite 

 constant entry rate between time-units 1 

 and 4. By time-unit 5 this entry rate is 

 decreased because the numbers available are 

 reduced. Since a time lag is required for 

 fish to ascend the fishway, the exit rate 

 does not reach a high level until time-unit 

 2; then it is sustained through time-unit 5. 

 It decreases by time-unit 6, since nezurly 

 all available fish now have passed. 



This, briefly, is the type of passage 

 encountered in practice (filling and Raymond, 

 1959). The difficulty is in collecting 

 sufficient numbers of fish to sustain, to- 

 gether, the entry and exit rates long enough 

 to yield a reasonable estimate of "maximum" 

 average number present. 



Under this definition of average num- 

 ber present, the relationship of figure 1 

 is complicated by the fact that the average 

 time applies to the entire test interval 

 while the average number present applies 

 only to a central portion of this interval. 

 To estimate the relationship of figure 1 as 

 precisely as possible, one should terminate 

 entry as soon as the entry rate begins to 

 decline. 



Factors other than the difficulty of 

 collecting large numbers of fish make this 



Figure 2. — Distribution in time of fish 

 entering and leaving a test fishway. 



type of experimentation difficult. For 

 example, the fish available for entry at any 

 time will represent a complex and usually 

 unknown combination of fatigue and motiva- 

 tion states. Further, the effects of fa- 

 tigue and motivation on observed performance 

 are complicated by the fact that species 

 composition chcinges from time to time in 

 most operating fishways. Thus, it will be 

 difficult to estimate the effects of crowd- 

 ing asid to consider at the same time the 

 effects of these other factors. Success in 

 this type of work will demand rigorous 

 attention to the principles of experimental 

 design. Perhaps small-scale studies will 

 provide data for a statistical separation 

 of effects where appropriate designs cannot 

 be adapted to practical demands on the 

 prototype scale. 



The ultimate test, of course, is 

 whether the experimental approach can be 

 mcide realistic enough to be useful. In 

 spite of the difficulties we now shall 

 attempt a definition of capacity. 



DEFINITION OF CAPACITY 



To define capacity as a quantity which 

 can be measured from the performance of 

 fish, we must combine our notions of average 



