56 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



per fish. In 1926, Smith (in: Gilbert- and Rich, 

 1927) examined ovaries from 40 females and ob- 

 served a mean fecundity of 3,728 eggs and a mean 

 mideye-fork length of 56.4 centimeters. A mean 

 fecundity of 3,237 eggs and a mean length of 55.4 

 cm. are derived from data given by Rounsefell 

 (1957) for 411 females examined from 1938 to 

 1941. The average length of female red salmon 

 in the 1958 escapement at Karluk Lake was 51 

 cm., and the average fecundity was 2,762 eggs. 



These data suggest a long-term decrease in size 

 and fecundity of red salmon at Karluk Lake that 

 may be real and thus an important consideration 

 in the declining abmidance of that stock. This 

 indication of a downward trend in size and fecun- 

 dity may also be due to sampling inadequacies. 

 The 40 fish studied by Gilbert and Rich (1927) 

 were collected on a single day, September 15, 1926. 

 The 411 fish included in the analysis by Rounse- 

 fell (1957) were taken chiefly from the spring 

 portion of the run. As we shall see in a later 



section, age and size composition of the run 

 changes during the season. Therefore, differences 

 in mean size and fecundity may reflect differences 

 within seasons as well as between seasons. 



Recent data on red salmon in Alaska show that 

 lengths and fecundity vaiy considerably. Mathi- 

 sen (1955) ' found for 1948 and 1950-52 that the 

 mean mideye-fork length of females at Pick 

 Creek (a tributary of Lake Nerka in the Bristol 

 Bay area) was 53.0 cm., and the average fecundity 

 was 4,011 eggs. Average lengths and fecundities 

 at Brooks Lake for 1957 were 55.5 cm. and 3,916 

 eggs, and for 1958 were 53.3 cm. and 3,898 eggs. 

 Average length was 51 cm., and average fecundity 

 was 2,762 eggs for 1958 at Karluk Lake. 



These differences are not due exclusively to vari- 

 ations in fish sizes between years or stocks. Real 

 differences in fecundity for fish of the same size 

 are sho^vn by Rounsefell (1957) and are'clearly 

 evident between Brooks and Karluk Lakes stocks 

 (fig. 2). 



VARIATION BETWEEN PAIRED OVARIES 



Although the maturation rates are the same for 

 eggs in the left and right ovaries (Rounsefell, 

 1957), the number of eggs in each side is usually 

 different. Brown and Kamj) (1942) state that in 

 brown trout {Salmo truffa) the posterior portion 

 of the intestine usually bends to the right, crowd- 

 ing the right ovaiy at its posterior end and maldng 

 it smaller than the left. No bend in the intestine 

 was detected in brown trout with ovaries of the 

 same size. 



Egg counts for left ovaries were plotted against 

 those of the corresponding right ovaries for 1957 

 and 1958 samples at Brooks Lake and for 1958 

 samples at Karluk Lake (fig. 4). Ninety percent 



of the left ovaries held more eggs than the right 

 in 1957 Brooks Lake samples, 91 ijercent in 1958 

 Brooks Lake samples, and 69 percent in the 1958 

 Karluk Lake samples. Red salmon at Bare Lake 

 on Kodiak Island have the opposite condition, 

 more eggs in the right o\aiy than in the left (Nel- 

 son, 1959). Karluk Lake data are consistent with 

 Rounsefell's (1957) findings in 1939, m which the 

 number of eggs in ovaries from small fish was 

 similar between right and left sides; but as the 

 total number of eggs increased, the proportion in 

 the left ovary l>ecame increasingly greater than 

 in the right. 



REPRODUCTIVE POTENTIAL OF SPAWNING POPULATIONS 



The number of salmon spawning in a locality 

 is often regarded as indicative of the reproductive 

 potential. Escapement figures have been used 

 since the inception of management of our salmon 

 resources to predict the strength of futuie runs. 

 However, considerable variability in the repro- 



1 studies on the spawning bioIoRy of the red salmon, Oncor- 

 huiichiix tierkn (Walhaum). in Bristol Bay, Alaslia, with special 

 reference to the effect of altered sex ratios. Ole A. Mathisen, 

 doctoral dissertation. University of Washington. 



ductive potential may actually exist indepentlent 

 of the actual number of spawners. 



Annual differences in sex ratios alone can cause 

 substantial differences in the number of eggs 

 available for deposition. Average fecundity for 

 female red salmon was relatively stable during 

 three years at Babine Lake (Withler, 1950), but 

 a high preponderance of males in one of these 

 years reduced by one-half the reproductive poten- 

 tial of that spawning population, even though the 



