Biological Studies: I 

 Field Orientation 



Co-Chairmen 

 W. Ebel 

 R. McConnell 



During the review of past research and throughout 

 the discussion of current research, a consensus of 

 opinion was developed concerning several points. 

 A general summary of these points is as follows: 



• Both adult and juvenile fish populations 

 suffer substantial mortalities if exposed for a suffi- 

 cient duration at levels exceeding 120% saturation 

 even though they have the option to sound and 

 compensate for supersaturation. 



• Adult mortalities that have occurred at 

 Bonneville Dam since 1955 have been related to 

 gas bubble disease and, in 1968, 20,000 adult 

 chinook were estimated lost in the vicinity of John 

 Day Dam. 



• Spawning ground surveys in the Columbia 

 and Snake Rivers have indicated a recent decline in 

 numbers of redds and these can be directly related 

 to years when supersaturation was high. 



• Percentage adult return of steelhead and 

 spring and summer chinook to the Snake River 

 have steadily declined since 1970, in spite of in- 

 creased production by hatcheries. 



• Mortality of juvenile populations of sal- 

 monids varies between dams and the cause of 

 mortality changes, depending on the flow and the 

 type of dam the fish must pass through. During 

 high flow years the majority of the mortalities 

 can be attributed to N^ supersaturation. However, 

 in low flow years such as 1973, all mortality had to 

 be the result of delays in migration rate, predation, 

 and passage through turbines. It was the consensus 

 that an extremely low flow year such as 1973 

 created much greater mortality to juveniles than 

 high flow years when supersaturation is present. 

 For example, Raymond (NMFS) estimated the 

 juvenile loss of chinook from the Salmon River in 

 Idaho to Ice Harbor Dam was about 50% in 1971 

 and 70% in 1972 (both high flow years) while in 1973 

 (a low flow year with no supersaturation) mortality 

 was about 88%. 



• Resident fish species and invertebrate 

 population also are affected by gas bubble disease. 

 Eighteen species of fish in the lower Columbia 

 River have been observed with gas bubble disease 

 and invertebrate species diversity below Libby Dam 

 has been reduced leaving primarily one species 

 (Chironomus sp.). 



• Knowledge of depth distribution of fish 



species is important when attempting to assess 

 mortality that might be caused by exposure to 

 supersaturation of N 2 . When levels of 130% are 

 recorded at surface pressures, juvenile salmon in 

 the Snake River are still subjected to levels of at 

 least 118%, even after accounting for the hydro- 

 static compensation indicated by their average 

 depth distribution. Studies of depth distribution by 

 Mains and Smith (1954-55) indicated that 44% of 

 the outmigrant chinook were in the top 2.5 ft of 

 water and 68% were near shore. Studies of depth 

 distribution at Lower Monumental by Smith (1973) 

 indicated 34% of the juvenile chinook and 27% of 

 the steelhead were in the top 5 ft of water. Prelimi- 

 nary tests to determine depth distribution in the 

 lower Columbia by use of a sonic fish detector 

 indicated 58% were in the top 5 ft. 



All three studies indicated more fish move- 

 ment occurred during the night hours. 



• Live cage studies done by Parametrix were 

 in agreement with past live cage studies. No mor- 

 tality occurred in a vertical cage even though levels 

 rose to 125% saturation. It was pointed out that 

 other live cage studies done earlier resulted in sub- 

 stantial mortalities in the volitional cage (as high 

 as 60% in the Snake River) but levels of satura- 

 tion were as high as 135 to 140%. 



• Intermittent exposure of juvenile salmon 

 increases survival over that recorded for constant 

 exposure to high levels of supersaturation. 



• Recovery of exposed juveniles with obvious 

 symptoms of gas bubble disease does occur but 

 nonlethal exposure of adults usually results in 

 death from secondary infection from some other 

 disease such as Columnaris. 



• Studies to evaluate devices for reducing 

 N, concentrations indicate that spillway deflectors 

 ate the best solution to date. All data obtained 

 indicate that they reduce N 2 levels substantially 

 from what would occur with the standard spillway 

 and no adverse effects to either juveniles or adults 

 passing through or in the vicinity of the devices 

 could be detected. 



Ebel: National Marine Fisheries Service, Seattle, Washington; 

 and McConnell: National Marine Service Fisheries, Longview, 

 Washington. 



774 Round Table Discussion 



