LIFE HISTORY OF LAKE HERRING OF LAKE HURON 329 



than the scale increment of the preceding year (the reverse of the natural law of 

 decrease of scale increment with age and slower growth rate of body), which seems to 

 prove that the scale increment of the year contracts after being deposited. 



G. A part of the scale is absorbed in the maturation of sex organs during the 

 spawning period, as, for example, in the salmon. 



7. Occasionally more than one ring forms per year. 



The author concludes that the "phenomenon of apparent change in growth rate" 

 is most likely due to some natural feature in the fish's or the scale's growth or to the 

 contraction of scales. 



Miss Lee's second suggestion, that the nets may act selectively in that they retain 

 only the largest fish of the youngest year group and exclude the largest of the oldest 

 year group, does not seem to apply to the lake herring. The pound nets in which the 

 herring are taken certainly do not exclude any fish because of large size. When it 

 is remembered that the greatest dimensions of the openings in the mesh of the pot in 

 which the herring are captured are only 1 ^^2 to IM inches {2}4 to 23^ inches stretched 

 mesh), it appears highly improbable that any considerable selection of size occurred 

 in the 3-year group. If we assume an average length of only 200 millimeters (8 inches) 

 for the smaller fish (the captured 3-year fish averaged 229 milUmeters in length), 

 their depth would be about 1^ inches.'^ Thus, the largest mesh of the pot about 

 equals the depth of the smallest 3-year fish; but the mesh that forms the back of the 

 pot is very much smaller (2 inches), and becomes the bottom in lifting. It is during 

 lifting that small fish escape through the bottom, and clearly the smallest 3-year 

 herring could hardly, if at all, get through the small mesh of the bottom while it is 

 being lifted. Their escape might account for the higher calculated and measured 

 average lengths of the 3-year fish, but it would not account for Lee's phenomenon in 

 the calculated lengths of fish of greater age. 



The third suggestion of Miss Lee that conditions of growth may be improving 

 and the younger fish actually are growing more rapidly is applicable to some of the 

 Saginaw Bay herring. 1 have found (p. 367) that the herring of all age groups actually 

 had grown faster during the first three years of life in the year 1919 and subsequently 

 than before 1919; but such increased growth rates can not affect the individuals of 

 the same year class but of different age groups differently in corresponding years of 

 life. And yet that is what must have happened if Miss Lee's third suggestion be 

 true, for the "phenomenon" appeared even when the age groups of the same year 

 class are compared. Thus, in Table 35, in the 1919 year class, the lengths for all 

 growth years increase with the use of younger age groups for calculation. All fish 

 of this year class presumably were living under the same conditions in 1920 and 

 doubtless reached about the same length at 2 years of age, yet the calculated lengths 

 vary inversely with the age groups. 



Elsewhere (Tables 32 and 33) it is shown that the male and female herring grow 

 at the same rate. This precludes, for the lake herring. Miss Lee's fourth suggestion 

 that females and males have different growth rates and may be present in the samples 

 in varying proportion. 



Miss Lee's sixth suggestion is that a part of the scale is absorbed at the time of 

 maturation of the sex organs. In that case a zone of the scale laid dow^l in the year 



'i This value for depth was obtained for 84 Lake Huron herring 220 millimeters or less in length (average 203 millimeters). 

 Both length and depth measurements were made by Doctor Koelz. 



