production. A primary aim of the limnological 

 studies was to determine if those lakes that usu- 

 ally support high population densities of salm- 

 on are basically the more productive. In other 

 words, do they have higher concentrations of 

 dissolved plant nutrients, higher standing crops 

 of phytoplankton, and higher rates of photosyn- 

 thetic activity? 



The only measure of salmon production avail- 

 able for all the systems is the average escape- 

 ment for recent years. To use this measure we 

 must assume that the average catch-to-escape- 

 ment ratio is about the same for all systems. 

 Although this ratio can vary somewhat, the 

 escapement levels provide a useful index of 

 salmon production. 



The systems are ranked in table 7 according 

 to: (1) the average sockeye salmon escapement 

 per square kilometer of lake surface for 1955-62, 

 (2) primary productivity as indicated by the 

 rate of carbon fixation by photosynthesis per 

 square meter of lake surface and per cubic meter 

 in the euphotic zone, (3) the standing crop of 

 phytoplankton as indicated by the concentra- 

 tion of chlorophyll a, and (4) the concentration 

 of total dissolved solids. 



The four systems with the higher rates of 

 primary productivity (considering both rate 

 per square meter and rate per cubic meter) pro- 

 duced more adult salmon per square kilometer 

 of lake (Karluk, Chignik, Igushik, and Wood). 

 Among the other systems the correlation be- 

 tween rates of primary productivity and salmon 

 production is not marked. The number of ob- 

 servations was too small in several of the sys- 

 tems to give reliable averages for primary pro- 

 ductivity and chlorophyll a values ; hence, the 

 true rankings of the lake systems may diverge 

 from those given here. 



The primary productivity and escapement per 

 unit lake area for the Naknek system are un- 

 usual. Although this system does not rank high 

 (no. 6) in rate of carbon fixation in the water 

 column under a square meter of lake area, it 

 does rank high (no. 3) in rate of carbon fixation 

 per cubic meter in the euphotic zone. Further- 

 more, the escapement per unit lake area is a 

 misleading statistic for this system because two 

 basins, North Arm and Brooks Lake, make up 

 about 32 percent of the area of the system but 

 usually receive only about 5 percent of the es- 

 capement. These two basins also have the lowest 



Table 7. — Rankimj of sockeye salmon nursery lakes of soulh- 

 u-estern Alaska according to average escapement density 

 {1955-62), primary prodtictivity, standing crop of phyto- 

 plankton, and total dissolved solids (1961-62) 



Primary 



productivity (rate Standing 



of carbon fixation) crop 



Per Per of phyto- Total 



square cubic plankton dis- 



meter meter fchloro- solved 



Escapement lake in phyll a solids 



per square surface euphotic per in 



System kilometer area zone liter) p. p.m. 



Rank Nttmber Rank Rank Rank Rank 



Karluk 1 8.350 2 2 2 3 



Chignik, _ 2 8,070 I 1 1 2 



Igushik 3 4,360 '3 "4 '7 '10 



Wood 4 2,340 4 5 3 6 



Alagnak 6 1,441 10 10 9 5 



Ugashik 6 1,338 9 9 6 8 



Kvichak 7 1,330 7 7 4 7 



Naknek 8 1,122 6 3 5 1 



Snake 9 290 '5 '8 '8 "9 



Nuyakuk,., 10 280 ' 8 '6 '10 ' 4 



' Only a few determinations were made: see tables 2 and 6. 



rates of primary productivity in the system. If 

 North Arm and Brooks Lake were not consid- 

 ered, the Naknek system would rank about no. 

 5 in terms of escapement and no. 4 or 5 in terms 

 of primary productivity. 



Measurements of the standing crops of phy- 

 toplankton (chlorophyll a concenti'ations) and 

 concentrations of total dissolved solids are not 

 clearly related to rate of production of salmon. 

 We cannot expect the standing crop of phyto- 

 plankton to be as sensitive a comparative meas- 

 ure of productivity as rates of carbon fixation 

 because of the problems of unknown rates of 

 turnover or utilization of phytoplankton by the 

 zooplankton. Similarly, our measures of total 

 dissolved solids do not give a good estimate of 

 the potential of a system to produce salmon be- 

 cause the phytoplankters need a proper balance 

 of nutrients. 



CAPACITY OF SPAWNING GROUNDS 



Our purpose in studying the capacity of the 

 spawning grounds was to determine whether 

 the space available is sufficient to produce 

 enough salmon fry to use the nursery areas fully. 

 In considering the amount of spawning ground 

 as a limiting factor, we first present information 

 on the size of past escapements and their char- 

 acteristics. Next we will estimate potential 

 spawning populations by using estimates of the 

 space available for spawning, estimates of the 

 space requirements of a spawning female, and 



418 



U.S. PISH AND WILDLIFE SERVICE 



