FISHERY BULLETIN: VOL. 71. NO. 3 



Figure 13. — Growth in weight of 1961 and 1962 year class 

 salmon. Confidence zones for the first three samples of 

 1961 year class were too small to be shown. Those for 

 the first three samples of 1962 year class were not calcu- 

 lated because the fish were weighed in groups. 



They postulated, "a very nice regulatory mech- 

 anism: the more fry present, the less each eats, 

 hence the slower it grows, and hence the longer 

 it remains at a size especially vulnerable to 

 predator attack." A similar mechanism prob- 

 ably produced the heavy losses and compara- 

 tively slow growth in the 1962 year class in 

 Happy Valley Reservoir. 



Hoover (1936) described the growth achieved 

 by Chinook salmon in New Hampshire Lakes. 

 The fish generally matured at 4 yr, when they 

 averaged about 2.3 kg. Where rainbow smelt, 

 O.smen/.s mordax, were abundant, however, the 

 salmon averaged 4.5 to 5.4 kg and one reached 

 7.3 kg. Hoover thus also implied a food regula- 

 tion of growth, with these impounded salmon 

 being capable of growth approaching that of 

 sea-run fish when abundant foods were present. 

 Similarly, Johnson and Hasler (1954) depicted 

 food and the space over which it was concen- 

 trated as a primary factor limiting trout growth 

 in the lakes they studied. At Happy Valley, 

 under circumstances of low competition, growth 

 by first-year and second-year chinook salmon 

 was rapid; increased size as obtained in the 

 New Hampshire lakes, however, would likely 

 not have occurred in the absence of a forage 

 fish or other large foods. 



The average weight of 62 g attained by mem- 

 bers of the 1961 year class at the end of their 

 first summer represented a more rapid growth 

 rate than usually found in stream-living 

 Chinook salmon juveniles. The 22 g average of 

 the 1962 year class, however, is close to that 

 estimated by Breuser (1961) for chinook sal- 

 mon in the Willamette River of western Oregon, 

 which grew from an average of 2.35 g in May 

 to 20.17 g in November. 



CONDITION 



The salmon gained condition during the 

 spring, and lost condition during the midsum- 

 mer when temperatures were highest (Figures 

 14 and 2). In 1961, condition increased again 

 in the fall to the highest level measured (1.38). 

 Neither age class gained condition in fall 1962, 

 likely because of more slowly decreasing tem- 

 peratures and the presence of a higher fish 

 density. The 1962 year class lost condition 

 during the 5-wk period after planting when 

 they were concentrated behind the seine. 



I 50 

 1.40 

 1.30 



ir 120 

 o 



S i.io- 



o 1.00 



a 



2 0.90 



80 

 70 

 060 

 50 



SAMPLE SIZE 

 MEAN 3rf^^^.^^ CONFIDENCE ZONE 



32' 



1961 YEAR CLASS 



1962 YEAR CLASS 



V4 



20 



—I r- 



-, , r- . . .  T 1 ' ' ' 1 ' "" ' ' ' ' ' ' ' ^ 



FMAMJJASONDJFMAMJJASOND 

 1961 



1962 



Figure 14. — Changes in condition factor of 1961 and 1962 

 year class salmon. Confidence zones of some samples were 

 omitted for reasons stated for Figure 13. 



During the winter, average weight increased 

 little, and may have decreased (Figure 13). 

 Average length slowly increased (Figure 14) 

 resulting in decreasing condition factor values. 



886 



