PROGRESS IN BIOLOGICAL INQUIRIES, 193 



561 



recognition of the fact that many of the changes in abundance of 

 fishes which cause the ups and downs in commercial yields are 

 largely due to variations in the reproductive success in different 

 years. It appears that conditions in certain years are favorable to 

 the survival of the spawning product of certain species ; other years' 



FiouRB 2. — Chart of the Atlantic coast of the United States from Cape Cod to Cape 

 Hatteras, showing the oceanographic stations of the Albatross II during 1930 



conditions may result in virtually total mortality of the young which 

 that year might have contributed to the stock. These successes or 

 failures leave their impress on the population so that the yield of 

 the commercial fishery in subsequent years will be large or small 

 depending on whether the year classes have to a large degree sur- 

 vived or have to a large degree perished. 



