308 BULLETIN OF THE BUREAU OF FISHERIES 



"For the calculation from the mdividual scales it is best to use the ordinary 

 scale formula, adding Eraser's correction, and further altering the computation by 

 the addition of a correction obtained from the average (regression) line. This change 

 can be computed for the various year groups by projecting a line from the average 

 size of the year group in question back to the base line at a point corresponding to 

 the length of the fish when the scale was first laid down. The difference between 

 this line and the actual curve is then added or subtracted, as the case may be, to the 

 length obtained by the use of the corrected scale formula [p. 57]." 



Menzies and Macfarlane (1926, 1926a) observed Lee's "phenomenon" m the 

 calculated lengths of salmon, which, though of different ages, belonged to the same 

 year class. They asserted that the discrepancies are greater than might be expected 

 from late scale formation alone. The "phenomenon" does not seem to be due to 

 some obscure phenomenon of scale growth, but rather to some interrelation between 

 smolt size and length of stay in the sea and possibly to some racial differences and 

 variations in the food supply of different spawning tributaries. 



Nail (1926, 1926a) makes no corrections in the length computations of sea trout 

 inasmuch as they are fau'ly accurate. He writes, "It should be noted that the 

 figures in the summary do not confirm Mrs. Williams's (Lee) contention that, unless 

 allowance is made for the length of the fry before scale formation begins, the measure- 

 ments for the earliest stage of life will show a progressive diminution as larger and 

 larger fish are taken." 



To obtain du'ect experimental evidence on the validity of the scale formula in 

 the laboratory is extremely difficult on account of the small amount of body and 

 scale increments and of the relatively large amoimt of methodical or personal errors 

 involved. To overcome these difficulties, a large number of individuals must be 

 employed. My attempt to test the formula on the New York Aquarium whitefish 

 was therefore doomed to failure. Only few investigators have grasped the oppor- 

 tunity to obtaui such experimental data. 



Milne (1913) measured the photographs of scales of two salmon kelts captured, 

 marked, measured, and recaptured, and calculated the length of each fish at the time 

 of its marking. His calculated lengths exceeded the true lengths by one-half inch in the 

 27-inch salmon and by 6 inches in the 2634-uich fish. Milne concludes that either 

 the latter scale is abnormal "or that Dahl's system of measurement is not applicable 

 to a fish that has spawned." As the measurements from different scales of the same 

 fish seldom agree exactly, the author believes that it is not safe to rely on one scale 

 alone for the calculated length values. 



Wmge (1915) compared the growth increments of the body and the anterior radius 

 of the scales of four cod captured, marked, measured, and recaptured. Li his ratios, 

 given below, the denominator denotes the percentage the length of the cod, at its 

 marking, was of that at its recapture; the numerator denotes a similar value for the 

 scales. If body and scale had gi'own in direct proportion to each other, each ratio 

 would have equaled unity. 



n 1 T 0-8Q0 1 ,n n J TT 0-713 ^ „„ 

 Cod I, Q-;j^=1.10. Cod II, 0^^=0.99. 



Cod III, ^^^ = 1.06. Cod IV, Q-g^ = 1.03. 



