PERCENTILE PROPORTIONS OF LAKE AND ATLANTIC SALMONS. 



TABLE 23. 



137 



Countable Structures, Usually Referred to in Taxonomic Descriptions, as Derived from Individual Salmon 

 Comprised in the Basic Table from which the Previous Tables were Computed. 



Summary. — In a number of the comparisons of averages there is strong evidence of 

 divergence of lake salmon from Atlantic salmon. Atkins mentioned certain characters 

 which indicated the retention of juvenile characters in adult lake salmon such as parr 

 marks. The red spots of the Presumpscot River 'Jumper' is another mark of the same 

 nature. Another strong evidence is that the proportions of so many length-classes, 

 particularly breeding fish equal the proportions of the parrs of the Atlantic salmon. 



According to the averages of proportions the lake salmon average a somewhat longer 

 head, longer maxillary and longer mandible, but the most pronounced cUfferences are 

 in that portion of the body back of the dorsal and ventral fins. It is this region of the 

 body of the Atlantic salmon, which Menzies said grows more slowlj' than the anterior 

 part. 



It has been seen that the distance from the dorsal to the adipose fin averages shorter 

 in the lake salmon than in the Atlantic salmon and nearly all of the proportions for the 

 length classes are equal to the parrs of the Atlantic salmon, wliich is a character of the 

 young Atlantic salmon. The same may be said of the distance from the ventral to anal, 

 excepting that the Grand Lake and Sebago Lake breeding fish do not equal parrs in 

 their proportions. 



The averages for the caudal peduncle afford still further evidence in that all but three 

 of the ten length-classes of lake salmon equal those of the Atlantic salmon only in the 

 parrs, which are higher than any of the other length-classes of Atlantic salmon. 



The most salient difference between the lake salmon and the Atlantic salmon (ex- 

 clusive of the parr) is in the ratio of the least depth of the caudal peduncle to its length 

 from the dorsal and anal fins to the upper and lower base of the caudal respectively. 

 This difference may be expressed as foUows: 



Average for the least depth of the caudal peduncle not over 73 per cent of the dis- 

 tance from the adipose to the base of caudal and not over 66 per cent of the distance 

 from the anal to caudal Atlantic salmon {Salmo solar). 



Average for the least depth of the caudal peduncle more than 73 per cent of the dis- 

 tance from the adipose to the base of caudal and more than 66 per cent of the distance 

 from anal to caudal Lake salmon {Salmo sebago). 



