302 BULLETIN OF THE BUREAU OF FISHERIES 



In a second paper Lea (1911) applied his formula and showed that the annulus in 

 the scales of herring formed during the winter months. 



Dahl (1910) applied Lea's formida to the scales of the Norway salmon and trout 

 and found that the calculated and empirical measurements agree almost exactly. 



Sund (1911) noted a lack of agreement between the actual and calculated length 

 values in the sprat {Clupea sprattus) and found what was designated by Lee (1912) 

 as the "phenomenon of apparent change in growth rate." Lee undertook a critical 

 analysis of Lea's data and noticed that for corresponding years the total lengths 

 calculated from the scales of old fish were always lower than those calculated from the 

 scales of young fish; that is, the amount of calculated growth at corresponding ages 

 increases regularly as the scales used are taken from fish of younger age groups. 

 Thus, if the first year's growth increment is calculated from the scales of a 6-year 

 fish it is less than if calculated from scales of a younger fish. This "phenomenon" 

 has been found to characterize the uncorrected length computations of virtually all 

 species of fish studied and up to the present time has not yet been accounted for 

 definitely. Lee's is the first serious attempt to account for this apparent discrepancy 

 in calculated growth rate. Her proffered explanations are discussed in detail on 

 pages 328 to 329. 



Lea (1913) answers Miss Lee's paper with a pertinent discussion of his pub- 

 lished data and offers other statistics to prove that none of Miss Lee's explanations, 

 except one, can apply to his herring. To get a true picture of the "phenomenon," 

 Lea compared the calculated increments of growth, instead of the computed total 

 lengths, of fish belonging to different age groups but to the same year class and taken 

 by nonselective nets and considered the immature and mature individuals separately. 

 He analyzed the phenomenon as follows: (1) In the miniature hemng all correspond- 

 ing calculated annual increments decreased with each older age group employed. 

 (2) In the mature herring the corresponding calculated increments decreased v.ith 

 increased age of the fish used for the first three years of life, increased with increased 

 age for the next four years of life (4 to 7), and apparently remained constant with 

 increased age for the later years of life. Lea found that the decrease in the increments 

 was most pronounced in the period of sexual maturity. He explained this "phenom- 

 enon" on the basis that the largest individuals of a year class attain sexual maturity 

 first and then segregate from their own component and congregate with another 

 which consists of individuals sexually mature. Each year, then, the sexually mature 

 individuals of a year class congregate with the older spawning fish that comprise the 

 commercial catches until all the herring of a year class have matured. And, further, 

 the development of the sex products has a retarding influence on the mcrements of 

 growth. 



Hoek (1912) did not see how Lea's explanations could account for Lee's phenom- 

 enon and believed that it reflected on the accuracy of the scale method, so that a 

 comparison of calculated growth rates of fish of different year classes is unwarranted. 



Delsman (1913) believed that the low values of calculated lengths probably 

 were due to the slight contraction with age of the central, older parts of the scales 

 although he ascribed the "phenomenon" in his herring material to the selective 

 action of nets (1914). He concludes that on the whole the scale method is accurate 



