398 BULLETIN OF THE BUREAU OF FISHERIES 



Further evidence that the lengths reached by the herring in 1924 were not unu 

 sual may be found in the statements of Jordan and Evermann (1911), who visited 

 Bay Port, on Saginaw Bay, in 1908 or 1909. They write (p. 6): "The herring of 

 Saginaw Bay is also in all respects identical with the specimens from Collingwood 

 [Georgian Bay]. It is not only slender, as usual in this species, but reaches only a 

 small size,^ the average weight when mature being 6 ounces, those examined by us, 

 from Bayport, ranging from 2.5 to 9.5 ounces. The maximum length is 12 inches 

 and the usual from 9 to 10." I found that 500 mature herring taken in 1922 averaged 

 only 5.2 ounces in weight, and that my herring taken in 1924 averaged 242 milli- 

 meters or 9.5 inches, in length. The above authors do not give their standard for 

 comparison, but it is at least evident that their specimens were as large as if not 

 larger than mine. 



TEMPERATURE AND SUNSHINE AS FACTORS 



If I am right in concluding that factors that affected growth in Saginaw Bay 

 in 1915 to 1918 were local and not general over Lake Huron, we may ask what they 

 were. What growth-controlling factors operated in Saginaw Bay during the period 

 1915 (1916) to 1918 that were absent in the open lake. Did these factors exist, 

 also, before the period 1915 (1916) to 1918 and were they absent or reduced sub- 

 sequent to it? 



The first compound factor that suggests itself is that of temperature and light. 

 Temperatm-e may be considered first. Inasmuch as it was concluded that the 

 unfavorable conditions of growth were restricted to the Saginaw Bay region, fluc- 

 tuations in the mean temperature of the growing season probably may be excluded, 

 for temperature presumably should affect the growth rate of herring of all age groups 

 and of all localities on Lake Huron; but as reliable statistics of the air temperatures 

 of the Saginaw Bay region are available it is of interest to compare those of different 

 years with ascertained growth rates to see whether any relation is discoverable. 

 The temperatures of the water of Saginaw Bay for past years are not known. Neither 

 do we know the exact relation between these temperatiu-es and those of the air. 

 If the temperatiu-es of the air are to be used, we must assume that, in general, the 

 temperature of the water of Saginaw Bay is dependent on that of the air. That is, 

 if the air temperatures of the Saginaw Bay region show that a certain year was a 

 relatively cool one we must assume that the water of Saginaw Bay was, on the whole, 

 relatively cool in that year. The critical temperatures are presumably those of the 

 growth season, which for the young herring of Saginaw Bay very probablj' extends 

 from April to November. According to the fishermen, the bay is generally not 

 free from ice until April, while according to hatchery employees at Bay City, herring 

 eggs collected by them hatch some time in AprU. It is very probable, then, that 

 the wild immature herring begin their growth in April. It is not Ivnown how long 

 growth continues in the fall or whether it ceases entirely in the winter, though it 

 is virtually certain that growth is considerably retarded during the winter period. 

 However, irrespective of wliether we select as the growth season the period March 

 to November, April to November, or April to October, the conclusion derived from 



' Italics are mine. 



