30 THE ROYAL SOCIETY OF CANADA 



liaving spent two winters in fresh-water and two in the sea. They are 

 of the same age as the fully grown Sockeye, Spring and Dog Salmon, and 

 if the fact that so many of the fish that I examined belonged to this 

 group is an indication that the great majority of Stcelhead return to 

 fresh- water in their fourth year, it is interesting to note that the spawn- 

 ing run of this fish occurs typically when it is of the same age as the 

 three species of Oncorhynchus just mentioned; that is to say, the major- 

 ity of Steelhead running in any year will be fish from ova spawned 

 four years previously. But while the Oncorhynchi spend but one 

 winter in fresh-water, and three in the sea the Steelhead spend two 

 winters in each environment, agreeing in this respect with the Atlantic 

 Salmon. 



A very characteristic feature of the life history of the Oncorhynchi 

 is its definiteness. Apparently the life cycle does not typically extend 

 beyond four years, or, in the cases of the Coho and Humpback, beyond 

 two years, nor except in rare exceptions does any fish spawn more 

 than once in its lifetime. With the Atlantic Salmon the cycle is much 

 more indefinite. For it is known from the observations, especially 

 of Johnston, Dahl, Caldei-wood, Hutton, Malloch and others, that a 

 considerable number of these fish delay their return to the spawning 

 grounds until their fifth or even their sixth year. Furthermore, a 

 certain number of fish spawn more than once during their lives; not a 

 great number apparently, for Miss Esdaile,* from the records of 1,678 

 fish, after excluding all grilse and small Spring Salmon, found that only 

 6.4% of the remainder showed a spawning mark on their scales and 

 only about 0.4% showed two such marks. Since it may be assumed 

 that the presence of these fish in the river was an indication that they 

 were on their way to the spawning grounds, we have the result that 

 only 64 fish out of every thousand spawn more than once in their lives. 

 Nevertheless this proportion is probably far greater than that which 

 obtains for the Oncorhynchi, although the number of these that have 

 so far been examined is not sufficient to allow of a numerical statement. 



In view of the similarity of the life-history of the Steelhead to 

 that of the Atlantic Salmon it is interesting to note that agreement 

 also obtains in the two points just mentioned. For out of the twenty- 

 two Steelhead examined there were two whose life-histories had evi- 

 dently extended beyond the usual four years, and these fish constitute 

 the third of the groups that I have recognized. One of them measured 

 104.5 cm. in length and its scales (Fig. 4) showed, in the region repre- 

 senting the period spent in the sea, three check bands, instead of two, 



*Miss P. C. Esdaile— The Scientific Results of the Salmon Scale Research at 

 Manchester University. Mem. and Proc. Manchester Lit. and Philos. Soc. \'o]. 

 LVII. 1913. 



