402 



BULLETIN OF THE BUREAU OF FISHERIES 



I have shown (Table 39) that the 1-year herring showed a progressive increase 

 in growth rate in 1920, 1921, and 1922. To explain this progressive increase in 

 growth rate on the basis of heavy fishing we must beheve that the number of surviving 

 spawners became progressively less each successive fall below the normal during the 

 period 1918 to 1921, and that consequently competition for food among the young 

 herring grew progressively less severe during the period 1919 to 1922. That is, 

 fishing intensity must either have remained constant after 1918 or have become 

 more severe. This may or may not have occurred, we do not know; but in order to 

 explain the growth data of the 1-year herring on the basis of overfishing we must 

 accept this postulation as a fact. If fishing intensity had diminished after 1918, 

 the surviving spawners of each fall, and consequently the resultant fry, would have 

 increased in number and competition for food among the fry would have become 

 more severe. In that case the growth rate of the 1-year herring would then either 

 have remained constant or have decreased after 1918. 



What effect should such a constant or increased fishing intensity after 1918 have 

 had on the growth rate of the 2 and 3 year herring? If competition for food amongst 

 the older herring (2 years and older) in the open lake is not severe, fishing intensity 

 should not be a significant factor in the growth rate of tbese fish while in the open 

 lake. If, on the other hand, competition in the open lake is severe, fishing intensity 

 should be a factor. Competition may be an important factor in the early growth 

 of these fish in spring when they are in Saginaw Bay. In either case, whether com- 

 petition occurs in the open lake and in Saginaw Bay or in Saginaw Bay only, if the 

 number of surviving spawners each successive year fell more and more below the 

 usual number, competition among the older age groups in the open lake or in Sagi- 

 naw Bay would become less severe each year, and accordingly their rate of growth 

 while in the open lake or in Saginaw Bay would become progressively larger each 

 year. The second and third age groups should then show a progressive increase in 

 growth rate after 1918. This we know was not the case. 



It seems, then, that our data on the growth of the heriing can not be explained 

 by overfishing or intense fishing. If we interpret the growth history of the 1-year 

 herring on this basis, that, if we are consistent, of the 2 and 3 year fish must remain 

 inexplicable. If, on the other hand, we explain the growth data of the 2 and 3 year 

 herring on the basis of heavy fishing, those, if we are consistent, of the 1-year fish 

 must remain un explainable. Intense fishing would alter the growth rate of all three 

 age groups in the same fashion. 



Table 64. — Statistics of catch of herring for Saginaw Bay for the years 1916 to 1925, inclusive, 

 statistics were furnished by the Department of Conservation of the State of Michigan 



The 



'Taken from the biennial report of the Department of Conservation of the State of Michigan. 



