EBEL. PARK, and JOHNSEN: EFFECTS OF TRANSPORTATION 



straying. A steadily decreasing ratio of trans- 

 port/control numbers from the commercial 

 fishery below Bonneville to the spawning 

 grounds would indicate a loss of homing ability, 

 straying, or differential mortality between 

 groups. The ratios established for the test 

 gi'oup released at Bonneville were 1.7:1, 

 1.8:1, and 1.7:1 for the commercial fishery, 

 Ice Harbor Dam, and the spawning grounds, 

 respectively. This indicates that no loss of 

 the transport group occurred between Astoria 

 (Oreg.), Ice Harbor Dam, and the spawning 

 grounds. The same relation between ratios 

 exists if the returns from releases at John 

 Day and Bonneville Dam are combined; i.e., 

 no loss of the transport groups occurred be- 

 tween Astoria and Ice Harbor Dam. If the 

 homing ability of some fish was lost, any loss 

 of fish due to straying was compensated for 

 by an increase in survival and return of 

 transported fish to both the fishery and spawn- 

 ing grounds. 



Certain assumptions have been made to 

 determine, and then compare, ratios and per- 

 centage returns of fish from transported and 

 control groups. These are: 



1. No differential mortality occurred between 

 control and transported fish as they moved 

 upstream from the mouth of the river to the 

 spawning grounds; i.e., adult return ratios 

 of the numbers of transport/control fish in 

 the commercial and sport fishery in the lower 

 river can be directly compared with the ob- 

 served ratios at Ice Harbor Dam and the 

 spawning grounds to provide an indicator of 

 the effect of transportation on homing or 

 straying. 



2. The adult return ratio of John Day/ 

 Bonneville transported fish remained constant 

 after these fish entered the Columbia River. 

 We must assume this when the ratio is used 

 to determine the actual number of fish of the 

 John Day and Bonneville groups in returns 

 to the commercial fishery and to spawning 

 grounds (where the brands were not visible) 

 and when it is then necessary to rely on the 

 single tag code to calculate return data for 

 the two transported groups. 



3. Native and hatchery stocks in our control 

 and transported groups were recovered at the 



same rate by the detector and separator at 

 Ice Harbor Dam. This assumption is necessary 

 inasmuch as the estimated percentage return 

 of all adults to Ice Harbor (Table 4) was based 

 solely on the ratio of observed recoveries of 

 a hatcher>' stock (Rapid River stock) at Ice 

 Harbor and those subsequently recovered at 

 the hatchery. Recoveries of native fish on the 

 spawning grounds from fish identified at Ice 

 Harbor were insufficient for use in this appli- 

 cation. 



4. Rate of maturity and timing of migration 

 is the same for transport and controls. Since 

 ocean and river fishing rates are not the same 

 on fish maturing early and returning early 

 as they are on fish maturing late and returning 

 late, this assumption is required. 



The most significant result of this study is 

 that the ability of the chinook salmon and 

 steelhead trout to return to Ice Harbor Dam 

 was not destroyed or even seriously affected 

 by transporting seaward migrants around a 

 major part of their downstream route. Overall 

 returns from transported groups, except those 

 from the early releases at John Day Dam, 

 were significantly greater than those from the 

 control group. These results are radically dif- 

 ferent from any achieved to date in other 

 experiments (Ellis and Noble, 1960; unpub- 

 lished hatchery records of Washington, Oregon, 

 and California) where hatchery stocks exclu- 

 sively had been transported. We are therefore 

 convinced that our original hypothesis is 

 acceptable — namely, that a fish's experience 

 from the period beginning with smolting to 

 the time the fish is collected for transport is 

 critical. Our understanding of the mechanisms 

 of homing is still limited, however, and much 

 more must be learned to fully understand what 

 the critical factors are in determining what 

 is needed to provide anadromous salmon and 

 trout with homing cues. Experiments to pin- 

 point the critical requirements for imprinting 

 are needed. If these factors can be determined, 

 it might be possible to provide the necessary 

 experience in a hatchery prior to transport 

 which would enable transport of fish directly 

 from the rearing areas to locations downstream 

 and thus eliminate much of the usual down- 

 stream mortality and still achieve satisfactory 



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