[mcmurrich] pacific COAST SALMON 29 



therefore indicating a check in growth, occurs somewhere about the 

 middle distance between the nucleus of the scale and the periphery of 

 the fresh-water area, a second similar check band also occurring at 

 this periphery. 



This same arrangement occurs in the scales of the Atlantic Salmon, 

 and is there interpreted, on the basis of what is directly known as to 

 the life-history of that fish, as representing the two years spent in 

 fresh-water. The same interpretation may justly be applied to it in 

 the case of the Steelhead and it may be concluded that the fish spends 

 the first two winters of its life in fresh-water, agreeing in this respect 

 with the Atlantic Salmon, but differing from the Oncorhynchi. 



In the scales from the fish now under consideration, those ranging 

 between 63 and 68 cm. in length, the area occupied by the fresh-water 

 rings is succeeded (Fig. 2) by a broad zone occupied by rings widely 

 separated from one another, and to be taken as representing the first 

 summer spent in the sea. This zone is bounded peripherally by a 

 well-marked band of closely set lines, indicating a check in growth and 

 accordingly to be interpreted as representing the first winter spent in 

 the sea; and, finally, beyond these and extending to the margin of the 

 scale is a second zone of widely separated lines, representing a second 

 summer in the sea. 



The life-history, then, of these fish, as revealed by their scale 

 markings, may be summed up as follows, — The ova were spawned 

 probably during the late autumn and throughout that winter, the 

 following summer and the following winter the fish remained in fresh 

 water. In the spring of their second year they proceeded to the sea, 

 where they remained throughout their second summer and the following 

 or third winter, and were caught in their third summer. So far as the 

 time spent in the sea is concerned these fish are comparable to grilse 

 Spring Salmon or Sockeye and to adult Coho and Humpbacks, but they 

 were a year older than these, since they spent an additional year in 

 fresh-water. On the other hand they are exactly comparable to the 

 grilse Atlantic salmon, which are three year old fish, having spent two 

 winters and one summer in fresh-water as fry and parr, have descended 

 to the sea in their second summer as smolt and returned in their third 

 summer as grilse. 



Passing now to the consideration of the second of the groups into 

 which, on the basis of their scale markings, I have divided the Steelhead 

 examined, it is found to contain the great majority of the fish studied, 

 sixteen out of the twenty-two. The fish belonging to it vary from 74 

 cm. to 94 cm. in length, and, compared with the grilse already described, 

 each shows upon its scales an additional check band (Fig, 3) , indicating 

 an additional year spent in the sea. These then are four year old fish, 



