PROGRESS IN BIOLOGICAL INQUIRIES, 1933 327 



never extending to Nova Scotian waters. The transitory type, on the 

 other hand, appears in the United States fishery mainly in the siDring 

 and late fall and also usually extends along the coast of Nova Scotia 

 and even into the Gulf of k>t. Lawrence. 



Obviously, knowledge of the relative abundance of various year 

 classes together with their respective rate of decline acording to 

 type affords a basis for predicting future abundance of mackerel. 

 This in turn should permit the industry to plan its activities in 

 advance, thus ameliorating the otherwise disorganizing effects of 

 unexpected gluts and famines of supply. 



The knowledge essential for predictions is based on a measure 

 of relative abundance secured from an analysis of the catch per 

 mackerel vessel coupled with a study of the ages of the mackerel 

 present in the stock as judged from samples of the catches landed 

 by commercial fishermen. In 1933, as during former years, this 

 work w^as under the direction of O. E. Sette, assisted by F. E. Firth, 

 who made the necessary observations on the mackerel catch at Cape 

 May, N. J., during xA^pril ; at New York during May ; at Boston from 

 June to October ; and at Gloucester during November and December. 

 Of the 2,651 fares landed during 1933, aggregating 29,528,100 

 poimds, 1,G12 were recorded by localities of capture through inter- 

 views with captains and 881 were sampled to provide information on 

 the ages of mackerel, in the course of which 26,094 individuals were 

 measured and 1,733 scale samples were collected and subsequently 

 examined to determine the age of the fish from which they were 

 taken. 



The 1933 season interposed unusual difficulties to biological study 

 because, by voluntary agreement among the vessel owners ancJ 

 operators, the activities of the fleet during most of the season were 

 restricted greatly both as to the periods of time each vessel was per- 

 mitted to operate and as to the maximum fare which each vessel 

 could land. These important modifications in the operations of the 

 fleet required the employment of special methods to determine the 

 abundance in 1933 relative to that of former years. However, by 

 applying appropriate corrections it appears that the abundance of 

 mackerel in 1933 was at least 22 percent greater than in 1932, and 

 that if the fleet had operated without restrictions the catch would 

 have been at least 55,000,000 pounds as compared with the actual 

 catch under the restrictions in force of 29,528,100 pounds. The first- 

 named quantity is within 2,000,000 pounds or 4 percent of the " high 

 estimate " given in our prediction for the season and withir 

 11.000,000 pounds or 25 percent of the " most probable estimate." 



Biologically, conditions in 1933 were of particular interest, for the 

 events of this year were critical in determining whether or not the 

 class of 1931 was of the persistent type. Prior to the opening of 

 the season it already had been concluded that the 1930 class was 

 of the persistent type, but there was considerable doubt as to the 

 type of the 1931 class. In predicting, the " most probable estimate " 

 was based on the assumption that it was of the transitory type 

 merely because the latter had occurred somewhat more often than 

 the former. Recognition that the 1931 class might be of the per- 

 sistent type formed the basis for the " high estimate." Inasmuch 

 as the latter would have been realized if fishing had been unre- 



69933—34 2 



