By comparison, in another trial 

 (June 25 -No. 3) in which the fish averaged 

 9.2 pounds, the observed maximum entry was 

 165 fish a minute. Entry rates given imply 

 net entry, i.e., the total pzissing the first 

 weir in the fishway less the number drifting 

 or swimming back downstream. 



Different release techniques were em- 

 ployed in tests Nos. 1 and 3. Fish released 

 in the May 1 trial were subjected to the 

 brail-raising procedure to achieve a com- 

 plete exit from the collection pool, but no 

 brail was used to encourage exit from this 

 area in the June 25 test. The surprisingly 

 high entry rate achieved in test 3 is note- 

 worthy inasmuch as no unusual means were 

 employed to create a maximum influx of fish 

 to the fishway. 



To examine further the entry charac- 

 teristics in each of the tests, the high 

 average entries for continuous 20-minute 

 periods were determined (table 2). The 20- 

 minute observation period was selected since 

 this was usually the longest period in 

 which appreciable numbers were available for 

 entry. By the time 20 minutes had passed, 

 entry rate usually fell off markedly be- 

 cause of declining numbers in the collection 

 pool. For the two tests in which the larg- 

 est numbers of fish were passed (May 1 and 

 June 25), the high average 20-minute entry 

 was 42 fish a minute when fish averaged 14 

 pounds, and 64 fish a minute when the aver- 

 age weight was 9.2 pounds. Converted to an 

 hourly basis, the expected entry rates would 

 become 2,520 and 3,840 fish an hour for the 

 respective size groups noted. 



The numbers leaving per unit time in 

 tests 1 and 3 (figs. 5 and 6) apply to the 

 observed passage over the last weir in the 

 fishway. For fish averaging 14 pounds, the 

 maximum observed exit was 40 fish a minute 

 and the high 20-minute average was 28 fish 

 a minute. Similarly, the maximum,exit for 

 fish averaging 9.2 pounds was 85 fish a min- 

 ute and the high 20-minute average was 40 

 fish a minute. On an hourly basis, the ob- 

 served exits for the respective size groups 

 would become 1,680 and 3,000 fish an hour. 



The observed maximum exit in each 

 trial was somewhat less than the observed 

 maximum entry. A possible explanation may 

 be that the number of fish available for 

 passage was continually decreasing as fish 

 began to enter and ascend the fishway. 



Thus, during the brief period that a maximum 

 entry was in effect, the exit was just be- 

 ginning to rise. By the time appreciable 

 numbers had accumulated in the upper levels 

 of the fishway and the exit approached a 

 maximum, the entry already had begun to de- 

 cline (figs. 5 and 6) because of depletion 

 of the original supply available for pas- 

 sage. Therefore, the observed maximum exits 

 may be less than might have been attained 

 had it been possible to sustain the high 

 entries for a longer time. 



Entry Capacity 



Entry capacity is defined as the 

 point at which a further increase in number 

 available for passage fails to produce a 

 corresponding increase in the entry per unit 

 time. The number of fish available for 

 passage in each of the five 1957 capacity 

 tests was converted to pounds so that each 

 test could be evaluated in terms of average 

 fish size (table 2). Then the maximum entry 

 per minute in terms of pounds was determined 

 for each test. This was based on an average 

 of the high 3-minute entry. The average of 

 a 3-minute period was selected in preference 

 to the maximum entry in a single minute to 

 dampen the possible effect of size fluctua- 

 tions between minutes. 



Figure 7 indicates a linear relation 

 between number of fish (in pounds) initially 

 available for passage and maximum entry 

 rate achieved. It is not patently clear that 

 an entry capacity was reached in any of the 

 tests. This observation is made with cau- 

 tion, since it is based on a limited number 

 of trials conducted during different periods 

 of the season. Additional comparisons, 

 particularly at higher availability levels, 

 will be necessary to substantiate this 

 observation. Since the present comparisons 

 cover 2 months within the migrational period, 

 species composition and environmental condi- 

 tions (water temperature and turbidity) did 

 not remain constant for all tests. These 

 factors may have had considerable bearing on 

 maximum entries realized within individual 

 tests. For this reason the three trials 

 (Nos. 3, 4, and 5) conducted on June 25 may 

 not be directly comparable with those of 

 May 1 and 8. 



Maximum Number of Fish Present 

 in the Fishway 



We have previously noted that the 



