330 



BULLETIN OF THE BUREAU OF FISHERIES 



of spawning, of a width proportional to the growth of the fish in length during that 

 year, is reduced in width at the spawning time and, with the resumption of growth 

 after breeding, a spawning mark is left on the scale. However, this suggestion appar- 

 ently does not hold for the lake herring, as no spawning mark nor any evidence of 

 absorption is shown in the relief structures on the surface of their scales. 



Miss Lee's seventh suggestion is that occasionally more than one ring (annulus) 

 forms in a year. If such accessory annuli were not recognized as such, but were 

 treated as normal annuh, the "phenomenon" might appear in the calculations. 

 This suggestion does not apply to the lake herring, however, if my conclusions are 

 well founded that normally only one annulus is produced each year and that this is 

 distinguished readily from the occasional accessory annuli. 



There remains Lee's first suggestion that the samples of fish are not representa- 

 tive of the year group, and her fifth that the newer part of the scale contracts with 

 age. Miss Lee is inclined to accept her fifth suggestion that the scale, especially the 

 flexible newest part, may contract whenever additional material is added to its margin. 

 To ascertain whether this is true in the herring scales, I measured, for the year classes 

 1918, 1919, 1920, and 1921, the scale diameters at the end of each growth year (Table 

 22). The average diameter increments derived from these measurements are shown 

 in the right half of the table. The increment of the fourth year of the 1918 year class 

 increases as the age of the fish whose scales were measured increases. Likewise, the 

 increment of the fifth year of this year class is less (0.27) in the 5-year herring than in 

 the 6-year fish (0.44). Similarly, in the herring of the year classes 1919, 1920, and 

 1921 the newly deposited portion of the scale, which presumably had not yet con- 

 tracted, is nearly always narrower than the corresponding older deposits, which 

 presumably had contracted. The increments of the third growth year are the same 

 (0.71) in the 3 and 6-year fish of the 1919 year class. It is realized that the most 

 recently deposited portion of the scales of these fish may not represent a completed 

 growth year, but as the fish were taken in November it is hardly probable that the 

 newly deposited zones of the scales of the younger fish would increase sufficiently 

 during the winter to exceed those of corresponding years of older fish. From the 

 foregoing it appears that those zones of the scale deposited after the third year grow 

 broader with time; they seem to expand instead of to contract as the fish grows older 

 and additional material is added to the margin of its scale. 



Table 22. — Average total length and average increment in length, in millimeters, attained by the diameter 

 of non-X scales at end of each growth year of Bay City herring hatched in 191S, 1919, 1920, and 

 1921 and captured in 1921, 1922, 1923, and 1934 



1 The last total length value of each row represents actual diameter measurements; the others represent the lengths of "annular ' » 

 diameters, tha t is, the parts of the diameter included in the various annuli. 



