376 



BULLETIN OF THE BUREAU OF FISHERIES 



the percentages at the end of each year are as follows: Year II, 45.4 per cent; year 

 III, 64.7 per cent; year IV, 72.1 per cent; and year V, 79.4 per cent. (Corresponding 

 figures for length, based on year VI are: year I, 49.2 per cent; year II, 71.7 per cent; 

 year III, 84.5 per cent; year IV, 91.1 per cent; and year V, 94.6 per cent; see fig. 40.) 

 In comparison with length, the rate of the proportional total weight increase is 

 small during the first years of life, for while more than three-fourths of the total 

 length reached by the species is attained at the end of the third year more than five 

 years are required for a similar amount of weight increase. The curves of Figure 

 40, based on the above percentages, show that after the second year weight increases 

 more rapidly than length. The sudden final acceleration in weight may be due to 

 the small number of individuals in the sLxth year. Of course this rapid increase in 



Fig. 41, — Average weight, in ounces, reached by male ( ) and 



female ( — . — ) Saginaw Bay herring in dilTerent years of life. 



The curve based on males and females ( ) involves 



larger numbers of specimens. Curves are plotted from the grand 

 average weights of Table 34 



weight is but an expression of the fact that at first these fish grow chiefly along the 

 horizontal axis and are therefore comparatively slender, while later growth occurs 

 principally along the other axes and the body acquires more depth and thickness. 

 From the point of view of the commercial fisheries it is not profitable to allow 

 the herring, at their present rate of growth, to become much older than 3 or 4 

 years. The increase in their average weight is about 19.3 per cent in the third 

 but only 7.4 per cent in the fourth and 7.3 per cent in the fifth year; or, stated 

 otherwise, the herring gain on the average 1.50 ounces in the third but only 0.58 

 and 0.57 ounce in the fourth and fifth years, respectively (Table 34); tliat is, 

 the increase in weight in the fourth and fifth years together is less than that of 

 the tliird year alone. If the nets are regulated for the 4-year fish (235 milh- 

 meters, or 9.3 inches, long measured snout to base of caudal and 5.61 ounces 



