LIFE HISTORY OF LAKE HERRING OF LAKE HURON 413 



compared. The "annular" scale-diameter measurement of a particular year of life 

 decreases as the age of the herring whose scales are employed increases. 



25. The scale (and body) increments of the first and second growth years of a 

 year class of the lake herring generally ilecvease as the age of the fish whose scales are 

 studied increases; but the scale (and body) increment of the third growtli year increases 

 or remains constant with age, while the scale (and body) increments of the fourth and 

 fifth growth years increase with age. 



26. Every factor that could possibly explain conclusions 20 to 25, inclusive, in 

 the lake herring was critically considered. It was concluded that these facts may be 

 interpreted best as the results of the following three natural events in the life history 

 of the herring: (a) Herring that reach sexual maturity late in life are the more slowly 

 growing individuals of their year class; (&) sexual maturation usually is accompanied 

 by a retardation in the growth of bodj' and scale; (c) a compensation in growth 

 occurs in lake herring; that is, herring that grow slowly during the earliest years 

 of life grow rapidly during the later years of life, and vice versa. According to 

 this view, then, Lee's "phenomenon" is largely a natural event and should 

 occur to some extent in calculations of growth based on the scales of adult 

 herring. The disproportionate growth rate of body and scale may be an additional 

 factor for the "phenomenon" in the computed lengths. It is believed that 

 late scale formation, which is usually considered to be the cause of Lee's "phe- 

 nomenon," is not such a factor, for (a) computations of growth are based on the 

 assumption that the lengths of the body and scales maintain a fixed relationship 

 after the first year of hfe; that the body-scale ratio of a fisli at death is the same as 

 it was at the time of the completion of each annulus on the scale, irrespective of the 

 actual growth relationsliip during the first year or dmiug the intervals between the 

 periods of annuli formation, for lengths are calculated back to the periods of annuli 

 formation (p. 320); (b) the rapid proportional increase in the length of the scale during 

 the first year of life counteracts late scale formation in its effect on the computations 

 of length (p. 340); (c) late scale formation can not be a factor in the "phenomenon" 

 found in direct measurements of scale diameters (p. 341); (d) corrections for late scale 

 formation do not eliminate the "phenomenon" from computations of growth; cor- 

 rected computations of length tend to be too high for the early years of hfe (p. 339). 



27. The life history of the lake herring described in this paper is based on four 

 large collections made at Bay City, Mich., on Saginaw Bay in the fall of 1921, 1922, 

 1923, and 1924. 



28. No 1-year herring and relatively few 2, 6, 7, or 8 year fish were found in the 

 commercial herring catches of Saginaw Bay. The 3, 4, and 5 year fish composed 

 87.2 to 97.4 per cent of the commercial catches. The fom-th age group was always 

 dominant, its individuals comprising 42.8 to 58.3 per cent of the total catch. The 

 oldest lake herring I have ever seen was in its eleventh yeir. 



29. The percentage of 3-year herring in the commercial catches of Saginaw Bay 

 increased each year dm-ing the period 1921 to 1923, then remained stationary in 1924. 

 This increase in the number of 3-year fish occurred at the expense of the 5-year fish 

 mainly, which each year became progres.sively less abundant. 



