that date two coho salmon that had behaved 

 identically to fish immobilized by decompression 

 were caught 6 min after release in the turbine. 

 They were quickly removed to individual holding 

 pens, where one recovered within 4 min and the 

 other within 62 min. The minimum travel time 

 from release point to the barge was about 3 min; 

 1 of the 3 min was required for travel from the 

 release point to the area of negative pressure 

 below the turbine blades. One of the coho salmon 

 was thus immobilized for a maximum of 9 min 

 and the other for 67 min after passing the tur- 

 bine blades. The recovery times of both fish were 

 within the range for recovery from immobiliza- 

 tion established in the laboratory. The two fish 

 were transferred later in the day to the shore 

 holding tank for observation of post immobiliza- 

 tion effects. Recovery was evidently complete, 

 for no adverse effects developed within 3 days. 



Hatchery-reared rainbow trout were used in 

 the seven tests that followed (Nos. 5-11); immo- 

 bilized fish were found in six (Table 1). The 

 relatively high frequency of recovery of affected 

 fish suggests that either rainbow trout were more 

 easily immobilized than coho salmon or that sam- 

 pling efficiency increased with time. The former 

 appears more likely — the three completely immo- 

 bilized trout caught in tests 6 and 7 (November 

 18, 22) remained immobilized several hours. The 

 exact time of their recovery or death was not 

 determined. They were still immobilized when 

 transferred from the barge to the holding tank 

 late in the day. One recovered during the night 

 and was alive 3 days later; the other two died 

 during the night. 



The four immobilized trout caught in tests 5, 

 9, 10, and 11 (16 and 30 November; 2 and 6 

 December) recovered on the barge while under 

 observation. At most, they were immobilized 

 from 19 (test 11) to 94 min (test 9) after pass- 

 ing the turbine blades. The minimum period of 

 immobilization ranged from 13 (test 10) to 77 

 min (test 9). The four fish survived a 3-day 

 holding period. The one caught in test 11 was 

 alive and evidently normal after 30 days of ob- 

 servation for possible development of latent 

 lethal effects. 



Although few immobilized fish were caught in 

 the turbine discharge, the small catch assumes 

 greater significance when the methods of cap- 

 ture are considered. Of the total turbine dis- 

 charge screened by the funnel net, slightly less 



than 1% entered the recovery barge; the rest 

 filtered through the meshes of the net. An esti- 

 rriated 18% of the test fish released in the turbine 

 were killed by impingement against the net and 

 a much higher percentage injured by physical 

 contact. 



For immobilized fish to reach the recovery 

 barge uninjured (not lacerated, descaled, etc.), 

 they would have to be passively transported the 

 length of the net by that flow directed toward 

 the cod end. 



Because the net may have caused immobiliza- 

 tion by impingement, it was highly desirable to 

 obtain samples of immobilized fish in the general 

 area occupied by the net in the 1966 tests. Field 

 parties with long-handed dip nets cruised the 

 area in boats just after releases in April and 

 May 1967 to search for fish in distress. Although 

 many such fish were seen to surface, most were 

 picked up by hovering gulls or pulled under the 

 surface by turbulence before they could be 

 reached. For the final test (10 May), a small 

 inclined-screen scoop trap (50.8 cm deep and 

 121.9 cm wide) was anchored in the turbine dis- 

 charge. It, too, proved of little value for col- 

 lecting distressed fish. The total catch by both 

 methods was only five immobilized fish. All of 

 them displayed the symptoms characteristic of 

 decompression, erratic motion followed by in- 

 activity and sinking. Observed immobilization 

 ranged from 2 to 6 min, and the computed max- 

 imum period of immobilization ranged from 6 

 to 18 min (Table 2). 



Inherent in this study is the assumption that 

 immobilization was due to decompression. The 

 assumption is supported by laboratory experi- 



Table 2. — Duration of immobilization of individual coho 

 salmon fingerlings caught by dip net and scoop trap 

 in the turbine discharge, 14 April - 10 May 1967.' 



Time Time 



from release u"^^ from release 



Date in turbine to . "®^.^?^ , in turbine 



1967 capture in immobilized to recovery 



dip net and observed Estimated Jl^.'i?,™: 

 scoop trap — v,.i,,„*,„ 



mobilization 



14 April 



21 AprU 

 10 May 



mm 

 3 

 5 



14 

 7 



11 



mm 

 5 

 2 

 5 

 4 

 6 



m.m 



7 



6 



18 



10 



16 



mm 



8 



7 



19 



11 



17 



All fish survived a 3-day holding period. 



