36 SALMON AND TROUT TN ALASKA. 



the natural food supply of the waters, since no steps are taken, or 

 perhaps can be taken, to increase that supply. It is notable that 

 Patching Lake, where wholly natural conditions yet exist, showed a 

 more favorable supply of plankton life than Heckman Lake. In 

 this connection it must also be noted that yearlings leaving the Naha 

 in 1903 averaged about 65 mm. in length. In the following year 

 there appeared a considerable reduction in the size, the average being 

 under 60 mm. This difference in the figures, however, might be due 

 in slight part to the greater number measured in 1904. 



The size of the yearlings at the time of their movement varies 

 more or less in different localities. In the Naha, in 1903, 943 speci- 

 mens averaged 65 mm., with extremes of 48 and 100 mm.; in 1904, 

 2,714 specimens averaged 59 mm., extremes 47 to 115. (See diagram 

 A".) In the Eraser River, as reported by Babcock, the average is 

 76 mm. Fifty-seven examples from the Wallowa River, Oregon, 

 taken April 20, averaged 100 mm., with extremes of 99 and 132 mm. 

 Besides these, in the same lot, were 6 females averaging 163 mm. 

 (extremes 155 and 178 mm.), which were distinct in size and did not 

 intergrade with the remainder. That they were not the dwarf form is 

 shown by the large number of eggs in the ovaries, the large sockeye 

 bearing always far more than the dwarf is known to contain. 



The presence of these large individuals raises the question of a 

 possible second winter's residence in the fresh water. Young sockeyes 

 were found in the Wannuck up to 150 mm, and in the Karluk up to 

 221 mm., with the spring migrants. The Karluk fish intergrade 

 with the smaller, indicating merely unusual growth. The only disturb- 

 ing factor in the Karluk data is the fact that some of the larger of 

 these young fish, taken June 25 at the mouth of the lake going up 

 stream, show such enlargement of the testes as to indicate approach- 

 ing sexual maturity. The largest male and the two females taken in 

 the same lot show no unusual precocity and the ovaries indicate the 

 large form. The maturing males may be the dwarf form, but it is more 

 probable that they are precocious individuals of the ordinary type. 



In the yearling sockeye the sexes run approximately equal. Of 

 1,550 of the 1904 catch examined, 51 per cent were males and aver- 

 aged 0.2 mm. greater than the females in length, the sexes standing, 

 respectively, 59.7 to 59.5 mm. It appears that the greater size of 

 the male becomes early characteristic. 



MIGRATION OF YEARLINGS. 



The migration of the yearlings seems to be wholly a matter of 

 instinct. In 1903 the Naha reached a temperature of 40° F. about 

 the middle of April. By the end of that month most of the ice was 

 out of the lakes, but the temperature had not risen further. By 



«0n diagram react " yearlings" for '" fingerlings." 



