6 150 \- 



E 



X 



I- 125 



100 - 



UJ 

 IS 



t 75 

 111 



> 

 < 



50 



25 



Coho 



° — live fish 

 • — deod fish 



C hinook 



April 



May 



June 



Figure 8. — Calculated regression lines of average body length 

 of samples of live fish (20 fish each) as compared to average size 

 of dead fish taken daily from shallow test tank during test. 



pronounced in the chinook salmon populations. Each 

 point on the graphs represents the average length of a 

 sample of 20 fish that were examined for gas bubble 

 symptoms during the test. The growth rate (length) is 

 not as great as might be expected in hatchery reared 

 populations. In the shallow tank, where the greatest 

 mortality occurred, it appears as though the smaller 

 fish, in each species, were the ones that succumbed 

 (Fig. 8). These are observations of general trends that 

 might be representative of these tests only. 



EFFECT OF WATER DEPTH ON 

 FISH SURVIVAL 



Comparing the accumulative mortality in the deep 

 (Fig. 5) and shallow tanks (Fig. 6), it is obvious that 

 the added depth of water in the deep tank did 

 enhance the survival of test fish. These data suggest 

 that the extent of mortality that occurred in the 

 shallow tank was possibly greater than that which 

 would occur in the river under the existing cir- 

 cumstances; however, this condition is not represen- 

 tative inasmuch as the young fish in the river are not 

 restricted to such shallow confinement. Neither 

 should we assume that the relatively "low" mortality 

 experienced in the deep tank represents all river con- 

 ditions that relate to mortality; for example, the fish 

 in our holding tanks were not subject to predation. 

 Although, one can argue, predators may also have 

 been affected by high concentrations of dissolved gas. 

 If dissolved nitrogen (at Prescott) had been con- 

 sistently above 130% of saturation, it is quite probable 

 that additional mortality would have occurred in the 

 deep tank. For example, Ebel (1971) showed that a 

 group of juvenile chinook salmon (of hatchery origin) 

 held in a cage for 7 days (in the Columbia River), in 

 which the fish could range from surface to 4.5 m, had 



a mortality of 68%. Nitrogen concentrations during 

 his test ranged from 127 to 132%. To make more 

 meaningful extrapolations from test results, we need 

 to know at what depths the majority of the fish in the 

 river are found, both resident and migrating species. 

 From work that has been done on vertical distribution 

 of seaward migrants, most investigators (Mains and 

 Smith 1964, Smith et al. 1968, Monan et al. 1969) 

 agree that the largest percentage of juvenile salmon 

 and trout can be found in the top 5 m of water; this 

 tends to support the hypothesis that results of tests 

 done in less than 1 m of water are not representative of 

 the populations of juvenile salmon and trout in the 

 river. There are other factors that may affect the 

 depth patterns of fishes, e.g., spawning behavior, light 

 intensity, water temperature, and turbidity. These 

 items should be examined in the future. The test out- 

 lined in this report should by no means be considered 

 conclusive, but results indicate that there should be 

 more biological data made available to State and 

 Federal regulatory agencies prior to establishment of 

 permanent water quality standards relating to gas 

 saturation in the Columbia River and its tributaries. 



ACKNOWLEDGMENT 



The National Marine Fisheries Service appreciates 

 the close liaison and cooperative attitude that prevail- 

 ed between NMFS and the Corps of Engineers during 

 this study. Technical representative for the Corps of 

 Engineers was Peter B. Boyer, Chief, Water Quality 

 Section, North Pacific Division. The technical 

 reviews, outlines, and suggestions of the Corps's 

 representative and his associates materially aided the 

 successful completion of our work as did the expertise 

 of Lawrence Davis and Maurice Laird, both 

 technicians with NMFS at the Prescott, Oreg., facili- 

 ty. 



LITERATURE CITED 



AMERICAN PUBLIC HEALTH ASSOCIATION. 



1971. Standard methods for the examination of water and 

 wastewater. 13th ed. Am. Public Health Assoc, Wash., 

 D.C., 874 p. 

 EBEL, W. J. 



1969. Supersaturation of nitrogen in the Columbia River and 

 its effect on salmon and steelhead trout. U.S. Fish Wildl. 

 Serv., Fish. Bull. 68:1-11. 

 1971. Dissolved nitrogen concentrations in the Columbia and 

 Snake rivers in 1970 and their effect on chinook salmon and 

 steelhead trout. U.S. Dep. Commer., NOAA Tech. Rep. 

 NMFS SSRF-646, 7 p. 

 MAINS, E. M., and J. M, SMITH. 



1964. The distribution, size, time and current preferences of 

 seaward migrant chinook salmon in the Columbia and Snake 

 rivers. Wash. Dep. Fish., Fish. Res. Pap. 2(3):5-43. 

 MONAN, G. E., R. J. McCONNELL, J. R. PUGH, and J. R. 

 SMITH, 



1969. Distribution of debris and downstream-migrating salm- 

 on in the Snake River above Brownlee Reservoir. Trans. 

 Am. Fish. Soc. 98:239-244. 



