328 U-S. BUREAU OF FISHERIES 



stricted, there is afforded convincing evidence that the 1931 class is 

 of the persistent type. 



With two important year classes present in the stock of mackerel, 

 both of them of the persistent type, which may be expected to suffer 

 only a gradual, moderate decline during the next decade, and since 

 these now dominate the catch, it appears that relatively high, though 

 gradually declining, abundance is assured during a number of years 

 even though no important new year classes appear in the immediate 

 future. Of course, the advent of such year classes would raise the 

 level of abundance still higher, perhaps halting the decline and 

 possibly causing heights of abundance exceeding any that have been 

 observed since the present studies were initiated. 



The results of predictions during the past 6 years have demon- 

 strated not only the practicability of the method but also have indi- 

 cated two primary weaknesses which must be eHminated if the system 

 is to attain the accuracy that is essential in the event that commercial 

 operations are to be adjusted to the prospective yield. These are: 

 First, lack of means to estimate the prospective abundance of year- 

 lings; and, second, inability to determine the type of year class 

 prior to its second year in the commercial fishery. We believe that 

 both of these difficulties may be overcome by appropriate investiga- 

 tion of the biological factors involved. To solve the first-named 

 question, the services of a suitably equipped research vessel are neces- 

 sary to survey the relative abundance of mackerel that are too young 

 to form a part of the commercial catch. The second probably would 

 yield to suitably designed, large-scale tagging experiments coupled 

 with morphometric analyses of the differences between year classes. 

 The personnel and equipment at present available are inadequate to 

 undertake these phases of the work. 



A further question demanding early attention involves the merits 

 of the present practice of catching large quantities of yearling mack- 

 erel. These mackerel are so small that disproportionately large 

 numbers of individuals must be caught to make up a moderate 

 poundage, and at the same time their worth in the market per pound 

 is usually only a fraction of that of fish only 1 year older. A solu- 

 tion involves a study of the losses through mortality and decreased 

 availability compared with the gains due to increased weight per 

 individual and increased price per pound. Here again much li^ht 

 might result from tagging experiments. 



With tagging looming as an important future technique, experi- 

 ments were undertaken during 1933 to determine suitable methods 

 of marking this delicate species. The results demonstrate the 

 feasibility of securing quantitative results from tagging methods but 

 at the same time they indicate extraordinary difficulties which can 

 be overcome only by special procedure that involves either the serv- 

 ices of a research vessel or a chartered mackerel-fishing vessel. 



The continued interest of W. C. Schroeder, formerly of the Bureau 

 of Fisheries but now with the Woods Hole Oceanographic Institu- 

 tion, in the migration of cod has made it possible to analyze the 

 returns from tagged cod released in 1932 and former years, though 



