PROGRESS IN BIOLOGICAL INQUIRIES, 1934 345 



ties. Tliey are fairly small (i/o to 1 pound each), have poorer keep- 

 iiigr properties than the larp;cr mackerel, and command a lower price 

 per i)0und. At the same time they are «i:rowin<^ fast and are destined 

 to double in wei<rht (lurin«r the next year. It is ap[)r()priate, there- 

 fore, to inquire whether a partial or total elimination of the yearling 

 mackerel from the catch might not be more than rejiaid by the 

 larger size and the greater value per pound of these fish in future 

 years. Essentially it is a question of whether apparent mortality 

 (rate of disa])pearance as measured by the catch per unit time of 

 fishing) is greater than the increase in value due both to increase in 

 poundage and ]irice per pound. 



The answer to this question is complicated by the fact that the 

 rate of disa]ipearance of yearling mackerel diifers greatly from one 

 year to another and that the differences are connected not with the 

 numbers caught out during the yearling year but with the type of 

 year class to which they belong. There appear to be at least two 

 types of mackerel in the western Atlantic; one, which we have desig- 

 nated as "persistent"; the other as "transitory." The former is 

 characterized by a low rate of annual disappearance, the latter by a 

 high rate. They ai'e distinguished by other peculiarities such as the 

 time and locality of greatest concentration and differences in rate of 

 growth. 



The existence of the two types with their different rates of disap- 

 pearance not only renders difficult a decision as to the merits of 

 exploiting yearling mackerel but also causes predictions to be less 

 assured and less definite. It is essential, therefore, to determine the 

 basis for the differences in behavior of these two subdivisions of the 

 population and especially to find means of distinguishing between 

 them at an eai'ly stage, in order to forese(> their subsequent decline. 



Naturally, the work during 1934 consisted of collecting and ana- 

 lyzing data necessary for determining the rate of catching and the 

 year class composition of the commercial run. This has been and 

 must continue to be the only means of a]:)])raising the current condi- 

 tion of the fishery. In addition, a new technique was employed to 

 analyze the size frequency distribution of the 9-year period to throw 

 more light on the nature of the two types of year classes, and the 

 catch statistics Avere reanalyzed to discover whether the periods of 

 presence of the two types were sufficiently distinctive and regular to 

 serve as a basis of within-the-season predictions. 



The work continued, as in the past, under the direction of O. E. 

 Sette. Field data were collected by F. E. Firth. They consisted of 

 1,413 interviews to obtain information on time and locality of 

 catches, measurement of 39,605 mackerel, and collection of 1,467 scale 

 samples. 



The prediction for 1934 was that the abundance would be the same 

 as in the previous year and that the catch by seiners would amount 

 to approximately 54.000,000 pounds if fishing were unrestricted, and 

 proportionately less if control of production were to take place under 

 provisions of the mackerel code. If these were to be of equal extent 

 to those employed by voluntary agreement, a catch of 28.000.000 

 pounds was to be expected. Actually. ]:)roduction conti-ol was exer- 

 cised during a smaller portion of the season and tlie catch was ac- 



31690— 3G 3 



