THE PROBLEM OF 



FISHWAY CAPACITY 



by 



Robert H. Lander 

 U. S. Fish and Wildlife Service 

 Seattle, Washington 



ABSTRACT 



The paper gives a rationale for studying the question of whether 

 or not crowding obstructs the passage of fish through a fishway. 



Average time spent in a fishway increases with numbers present if 

 crowding hinders passage. Average usage time plotted on average number 

 present (no delay from crowding assumed) yields the model. Capacity is 

 reached where values of observations exceed those in the model. 



Experimental data show, for a stable entry rate, a significcuit 

 decrease in the relationship of exit rate to numbers present. This is 

 suggested as one way of detecting delay from crowding in a particular 

 section; it requires only a single test. 



It is difficult to measure the capacity of a large fishway. 



INTRODUCTION 



How big should a fishway be? A fishway 

 too small (or otherwise inefficient) may 

 hinder the spawning migration of anadromous 

 fish, and thus reduce survival to the next 

 generation. On the other hand, a fishway 

 larger than required for efficient passage 

 is too costly. 



No criteria for measuring efficiency of 

 passage are accepted universally by fishery 

 and power interests. One might argue that 

 survival to the next generation is the most 

 realistic measure. But this kind of surviv- 

 al data would be both difficult and expen- 

 sive to obtain. 



Fishery scientists, working on runs of 

 anadromous salmonoids in a laboratory at 

 Bonneville Dam on the Columbia River, re- 

 cently have gathered another type of data 

 in prototype-Scale experiments: The numbers 

 of fish passing through a fishway per unit 

 time (filling and Raymond, 1959). These 

 studies are being fineuiced by the U. S. Army 

 Corps of Engineers, a major dam-building 

 agency concerned both with the need to pro- 

 tect the fish and the cost of doing so. 



From the cost standpoint it is realis- 

 tic to evaluate fishway capacity in terms 

 of numbers of fish per unit time. The net 

 efficiency of passage is the result of the 

 separate efficiencies at two stages: (1) 

 Attraction into a fishway, and (2) passage 

 through a fishway. One may apply an empiri- 

 cal notion of capacity to each stage. For 

 a given set of conditions, entrance capacity 

 may be defined as the maximum number enter- 

 ing a fishway per unit time; internal capa- 

 city, as the maximum number passing through 

 a fishway per unit time. If an entrance 

 can pass some maximum number per unit time, 

 unnecessary cost may be involved in building 

 a fishway of internal capacity greater than 

 required to pass this number. 



We propose here a rationale, leading to 

 a rough model, for evaluating the internal 

 capacity of a fishway. The need for such a 

 study arose in connection with the work 

 reported by Elling and Raymond (1959). 



I eun grateful to Dr. D. G. Chapman of 

 the Department of Mathematics, University of 

 Washington, Seattle, Washington for suggest- 

 ing the concept of average usage time. I 

 wish also to thank Glenn Pedersen and D. D. 



