332 BULLETIN OF THE BUREAU OF FISHERIES. 



of sea growth when captured. 4 Outside the narrow-ringed central area, which records 

 the life in fresh water, we invariably find in this species a vigorous summer growth, 

 succeeded by a well-marked winter check, and this in turn followed by an extensive 

 marginal growth of widely-spaced rings, which measure the growth of the current 

 season of capture. 



In the southern part of its range, where the coho uniformly spends one season in 

 fresh water before migrating seawards, the spawning run (aside from a few male grilse in 

 their second year) consists exclusively of 3-year fish. As we proceed northward, how- 

 ever, we encounter individuals that have tarried two years in the streams and are 

 maturing in their fourth year. These are more abundant in the Yukon than in any 

 other stream we have examined. Our small collection of 31 individuals comprises 12 

 that have spent one year in a stream and are 3 years old (see Figs. 286 and 287) and 18 

 that remained two years in fresh water and are in their fourth year (Fig. 288). If the 

 customary proportions are shown in this collection, some 60 per cent of the- young 

 spend two years in fresh water. One individual of our collection (Fig. 289) had appar- 

 ently spent three years in the river and was maturing in its fifth year. The number 

 of individuals at our disposal is too small in the various classes to give reliable averages. 

 Six 3-year males average 23.8 inches in length (middle caudal rays included, as in all 

 our measurements); four 3-year females, 24.6 inches. Eleven 4-year males (two years 

 in fresh water) average 24.5 inches; six 4-year females, 25.3 inches. As males are 

 consistently larger than females among Pacific salmon, we have additional reason for 

 distrusting the adequacy of the above figures. The 5-year male (three years in stream) 

 is 23 inches long. 



THE HUMPBACK SALMON (Oncorhynchus gorbuscha). 



Scattering humpbacks enter the river in July and August and are then so near 

 their spawning time that they would be unable to ascend the stream for any considerable 

 distance. We observed one ripe male at Andreafski on August 3 and were unable to 

 learn of the occurrence of the species beyond that point. 



The individuals observed were all small and without value, having often liquid 

 milt and partly free eggs. Four specimens measured from 20 to 22 inches in length 

 and weighed from 4 to 5 pounds. As in the case of all other humpbacks that have 

 been examined for age, these were in their second year and had proceeded to sea as soon 

 as free swimming, their scales registering none but sea growth. The small size was 

 doubtless due in part to the fact that they were maturing so early in the season, thus 

 greatly limiting the growth of the second year. The scales all indicated this history, 

 for the area representing growth of the second year was narrow and contained a partial 

 check at the margin. 



* We do not here include the lew male grilse, which in more southern districts mature during the first year at sea. 



