HIGLEY and BOND: CHINOOK SALMON IN A RESERVOIR 



NET PRODUCTION AND YIELD 



The production of a given group of organisms 

 was defined by Ivlev (1966) as the total elabo- 

 ration of tissue by that group over a given time 

 period, regardless of the fate of the tissue. 

 Ricker and Foerster (1948) used this viewpoint 

 with mathematical formulation to calculate 

 the production of juvenile sockeye salmon in 

 Cultus Lake. Allen (1951) described the graph- 

 ical method of computation which was used 

 here. 



Allen's method uses survival and growth in- 

 formation in plotting estimated population size 

 against average weight at successive intervals. 

 The area under the curve between plottings 

 (month intervals were used here) represents 

 the net production for that period. Survival 

 data are usually more difficult to obtain than 

 growth data, and deficiencies may introduce 

 considerable error into production estimates. 

 For example, estimated annual production in 

 Happy Valley by the 1962 year class would be 

 increased by one-half if mortalities were as- 

 sumed to have occurred later in the summer. 

 Despite such limitations, production estimates 

 are valuable measures for comparing the rear- 

 ing capacities of various bodies of water (Ricker 

 and Foerster, 1948). 



Both net production and potential yield were 

 computed for salmon impounded in Happy 

 Valley during 1961 and 1962, and compared 

 with values obtained for fish in other bodies of 

 water. Extrapolation of sui'vival and growth 

 curves through December 1962 was required 

 to make the 1962 computations. Annual pro- 

 duction for first-year salmon was considered to 

 be the tissue produced from planting until 31 

 December. Production by rainbow trout and 

 1959 year class salmon was not computed. 

 Because production was concentrated in the 

 summer, the average summer surface area of 

 6.1 hectares was used in comparisons with other 

 bodies of water. 



Total production by the 1961 year class in its 

 first year was 972 kg (159 kg/hectare). A 

 similar biomass — 1,039 kg (170 kg/hectare) — 

 was elaborated by the 1962 year class in its 

 first year, with less individual growth being 

 attained by larger numbers of fish. In 1962, 



production by yearling salmon was only 217 kg 

 (35.5 kg/hectare), or 22% of their production 

 in 1961. Reduced population size and slower 

 growth created by competition from the 1962 

 year class apparently caused this low produc- 

 tion. Much of the 217 kg elaborated depended 

 on the consumption of foods different from 

 those used by the younger salmon and on the 

 consumption of the younger salmon themselves. 

 Total production by both age classes in 1962 

 was 1,256 kg (206 kg/hectare). In both years, 

 about 75% of the production occurred from 

 June through September. Similarly, two-thirds 

 to three-quarters of the sockeye salmon pro- 

 duction in Cultus Lake occurred between 15 

 June and 15 September (Ricker and Foerster, 

 1948). Gerking (1962) stated that, "production 

 is an event of the summer," for the bluegill, 

 Lepomis macrochirus Rafinesque, of the Indiana 

 lake he studied. These observations simply as- 

 sert the importance of the limited growing 

 season in temperate waters. 



The potential yield of salmon tissue from 

 Happy Valley is here defined as production 

 surviving to the end of the year. This was cal- 

 culated as the biomass introduced at planting 

 subtracted from the standing cx'op present on 

 31 December. Standing crop was estimated by 

 multiplying the number of surviving fish (Figure 

 11) times their average weight (Figure 13). 

 Potential yield of first-year salmon on 31 De- 

 cember 1961 was 98 kg/hectare, and on 31 

 December 1962 was 73.5 kg/hectare. These 

 yields amounted to 61% in 1961 and 43% in 

 1962 of the tissue produced. Coche (1967) es- 

 timated 59.4% was the yield of first-year steel- 

 head trout, S. gairdmni from a western Oregon 

 reservoir. Survival in Coche's experiment was 

 38.4% as compared with 13% and 15% for the 

 two year classes in this study. 



Coche (1967) has summarized net production 

 values for a variety of streams and impound- 

 ments. Salmonids studied in oligotrophic lakes 

 produced from 0.6 to 65 kg/hectare/yr, those 

 in dystrophic lakes 19 to 84 kg/hectare/yr, 

 and those in North American streams 41 to 

 198 kg/hectare/yr. Brown trout, S. trutta Lin- 

 naeus, in a New Zealand stream produced 275 

 to 837 kg/hectare/yr. Largemouth bass, Micro- 

 pterKs mlmoides (Lac6p6de), in fertilized ponds 



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