14 BULLETIN OP THE BUREAU OF FISHERIES. 



The smaller size of the fish taken within the mouth of the creek near Point Ellice 

 is of interest and may be accounted for by one of two hypotheses: (i) These may be 

 fry which are just migrating from the stream into the Columbia estuary. It is not known 

 definitely whether chinook salmon spawn in this stream, but it is rather unlikely. Two 

 attempts were made to determine this, but only silver salmon were obtained. The 

 stream is quite small and is not a typical chinook stream, being for the most part shallow 

 and with sandy bottom. Furthermore, since the stream is so near the ocean, it should 

 be expected, owing to the warmer and more equable climate, that development would 

 be more rapid than in the higher tributaries. If this were the case, it would be expected, 

 unless growth were modified by some other factor, such as racial difference, that the 

 fish coming from this stream would average larger than those from the higher tributaries. 

 (2) The more probable hypothesis is that the smaller individuals among the migrating 

 fry have run up into the mouth of the stream. This might be for the sake of the probable 

 greater safety in such a location or because of the reduced salinity of the water. It 

 has been shown by Rutter (1903) that the larger fry are more resistant to the effects 

 of salt water, and also that alternations in the salinity of the water are a distinct aid 

 in accustoming the young fish to sea water. The second hypothesis, therefore, seems a 

 reasonable explanation for the presence of the smaller fish in the mouth of this stream. 

 It is quite probable that if these fish remain for any length of time in the fresh water of 

 such a stream it will have a tendency to slow up the growth rate and result finally in 

 developing irregularities of scale growth. 



Among those fish taken in the Columbia estuary proper it has been shown that those 

 specimens whose scales show a band of intermediate rings average larger than those 

 whose scales do not show this band. Since the wider rings indicate a more vigorous 

 growth this result was quite to be expected and hardly calls for special comment. It is 

 worthy of note, however, that the estimated length of the fish at the time of beginning 

 this intermediate growth is distinctly less than the length of those fish which have not 

 begun this intermediate growth. This estimated length was found by the method in- 

 vented by Dahl and since used to advantage by Gilbert, and also by Fraser. This method 

 involves the following proportion : 



Total length of scale : total length of fish : : the length of the scale at some particular point : the 

 length of the fish at the time this point was at the periphery of the scale. 



By applying this proportion to each individual it is found that in the 16 individ- 

 uals which have formed an intermediate band the average length at the time this inter- 

 mediate growth was begun was 53.3 mm. The average length of those fish present in 

 the estuary at this time, but which have not begun the intermediate growth, is 75.1 mm. 

 This shows that the fish whose scales do not have an intermediate band have arrived 

 in the estuary more recently than those whose scales do show this band of wider rings. 

 The greater length of the fish which have been longer in the estuary is the result of the 

 more rapid rate of growth maintained in the estuary as compared with the slower growth 

 in fresh water upstream. The cause of the accelerated growth in salt water is at present 

 unknown but is probably due to the increase in the food supply. One other possibility 

 suggests itself in explanation of the fact that some individuals do not show the more 

 rapid intermediate growth, namely, some individuals may not respond as readily (or 

 perhaps not at all) to the stimuli encountered in the estuary which, in other individuals, 

 initiate the accelerated growth. 



