may have been as young as 4 months and as old 

 as 7| months from known possible dates of 

 winter-run egg deposition. This may be com- 

 pared with the catch of 73 young chinook salmon 

 taken in the same way at the same site during 

 April 1952. These 73 fish are assumed to be 

 a mixture of spring-run and fall-run migrants. 

 They may have been as young as about 4 

 months or as old as almost 7 months from 

 probable dates of egg deposition. The two 

 groups have similar size ranges, but the aver- 

 age size of the 73-fish group is not available. 

 It appears that both groups were likely to have 

 been about 6 months old, on average. Since the 

 25-f ish group had experienced somewhat higher 

 average water temperatures, they should have 

 been of larger size, as seems the case. 

 Sampling during August through November is 

 needed to place limits on the downstream 

 migration of the winter run. It may be that 

 their migration, fitted to pre-Shasta Dam 

 conditions, does not begin until November, 

 or it may begin earlier in agreement with 

 other Chinook races in California. We have no 

 sampling earlier than November; hence we can- 

 not make a choice between these possibilities. 



DISCUSSION OF ENVIRONMENTAL 

 CONTROLS 



Although the winter run recovered quickly 

 from near extinction to a notable abundance 

 4 years later, it is only now reaching an 

 abundance comparable to the fall run, after 

 more than 15 years. It is possible that the 

 observed buildup is as rapid as can be ex- 

 pected with any introduction. Since these fish, 

 prior to Shasta Dam construction, were prob- 

 ably abundant only in the McCloud River, they 

 were, in effect, transplanted or introduced into 

 an entirely new habitat many miles down- 

 stream and many feet lower in elevation. The 

 new habitat has cold water temperatures 

 simulating the original home stream. However, 

 mine-waste pollution, which was not present 

 in their McCloud River habitat, may have been 

 harmful to the adults. If downstream migration 

 of the young of this race is delayed until fall 

 rains, the competition with trout and other 

 competitors and predators may have more 

 effect on this race. On the other hand, losses 

 of migrants into irrigation pumps and diver- 

 sions might be higher in other races, if the 



great proportion of the winter-run migrants 

 descend in November. 



Finally, in the holding areas below Keswick 

 Dam, the adult fish are much more vulner- 

 able to sport fishermen and poachers than they 

 were in their ancestral home. They bite well 

 and are much sought after, so that it is not 

 surprising that the sport-fishing take in the 

 rivers is proportionately higher with this race 

 than with the fall or spring run. The sport and 

 commercial take in the ocean may be smaller, 

 however, because of the lateness of the run. 



The habits of this run obviously adapt it to 

 situations below large reservoirs as well as 

 to spring-fed streams where suitable tem- 

 peratures of 50O to 570 F. can be maintained 

 during the May through August spawning and 

 incubation period. These fish also should be 

 ideally adapted to water temperature regimes 

 of the southern hemisphere. However, the 

 maturation of the eggs of winter-run fish under 

 conditions of increasing daylight and increasing 

 water temperatures, in opposition to condi- 

 tions experienced by all other chinook salmon 

 runs, is a fact to be carefully considered. 



These fish, historically, were apparently 

 adapted to streams fed largely by the flow of 

 constant-temperature springs arising from the 

 lavas around Mount Shasta and Mount Lassen. 

 The McCloud River, their known home is re- 

 nowned for its spring-fed flow, damped fluc- 

 tuations, and stable, low temperatures (46° F. 

 at Big Springs). Other streams in the vicinity 

 such as Fall River and Hat Creek, both tribu- 

 tary to Pit River, and Battle Creek, tributary 

 to mainstem Sacramento River, derive part of 

 their flow from springs. Many other streams 

 have cool flows in their headwaters. Since the 

 range of suitable hatching temperatures is 

 limited on the low side as well as the high 

 (42.50-57.5° F.— Combs and Burrows, 1957; 

 Brett, 1959), it may be questioned whether 

 any but a predominantly spring-fed stream 

 could provide suitable temperatures for sus- 

 tained production of winter-run fish. Cold, 

 fluctuating, snow-melt streams would be little 

 better than flashy, warm, rain-flooded streams. 

 In any case, little evidence is extant that this 

 run was distributed widely or that it ever was 

 composed of large populations prior to Shasta 

 Dam. 



