SALMON AND TROUT -IN ALASKA. 69 



The New Zealand experiment in acclimatizing salmon indicates 

 that both the sockeye and the king reach maturity at the age of 4 

 years. These two species have been successfully transplanted to 

 New Zealand waters, and runs of mature well-developed fish returned 

 in 1906 to the respective streams in which they were placed. An 

 account of the results will appear in the Proceedings of the American 

 Fisheries Society for 1907. 



FACTORS INFLUENCING RETURN TO FRESH WATER. 

 SEX INSTINCTS VERSUS CONDITION OF NUTRITION. 



The stimulus wliich it is assumed impels the salmon to seek again 

 the fresh water is approaching maturity. Many laiown facts bring 

 this assumption into question. The study of the Atlantic salmon by 

 the Fishery Board for Scotland led to the conclusion that in that 

 species the state of nutrition is the factor determining migration 

 toward the river; that when the fish has accumulated the necessary 

 supply of material it tends to return to its original habitat. In this 

 conclusion it is assumed that the present sea-running race has been 

 derived from a permanent freshwater-residing form. On the other 

 hand it has been assumed for the Pacific salmon that at the time of 

 separation of the early run to begin its travel into the stream, all of 

 that school of salmon — both those that are to leave the sea at once 

 and cease to feed and those that are to remain and continue to feed — 

 are equally well nourished and equally developed. It is known that 

 heavy floods in the springtime bring heav^^ spring runs, and cor- 

 respondingly poor fall runs, and it will be shown that the early 

 arrivals in Alaskan short streams are not so heavy in proportion to 

 length as late arrivals. In all salmon the cessation of feeding upon 

 or just previous to entering the fresh water brings a peculiar factor 

 into the problem. When they start for the spawning beds the fish 

 have two demands upon their supply of energy-producing stores, 

 i. e., energy for the work of ascending the rivers, and material for the 

 growth and development of the sex product — spawn and milt. In 

 the case of fish entering long rivers, such as the Columbia and Fraser, 

 the early run enters with a slightly developed generative product to 

 build up and the entire trip to the headwaters to perform. The 

 late run arrives with more fully developed sex organs and a much 

 shorter journey to make. 



Since no fish known to enter the streams fail to become sexually 

 mature the same season, and since fish retained permanently in fresh 

 water do not mature the sex product until they have reached the 

 appropriate age'^, it must still remain as the most reasonable con- 



«See Rutter, Bulletin U. S. Fish Commission, vol. xxii, 1902, p. 109. This can 



not be cited as an exception to the above statement, since the assumption that the 

 precocious maturation is due to residence in fresh water has no other support, and, 

 moreover, sea-run males are known to return as sexually mature grilse. 



