150 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Among the commercial fishes, the mackerel is remarkable for its spectacular 

 changes in yield. To illustrate this, only a few records need be selected (Sette and 

 Needier, 1934, p. 25). From 116,000,000 pounds in 1834 the United States catch 

 dropped to 23,000,000 pounds in 1840, only to rise again to 137,000,000 pounds in 

 1848. From its peak of 179,000,000 in 1884, the catch dropped to 30,000,000 in 188(3, 

 o;dy 2 years later. More recently it increased from 13,000,000 pounds in 1922 to 

 08,000,000 pounds in 1926. For the United States and Canada together the largest 

 catch, 234,000,000 pounds, was landed in 1884, the lowest, 12,600,000 pounds in 1910. 



Although these fluctuations had profound effects both on the economic welfare 

 of the fishermen and on the business of the fish markets, and although speculation, 

 both popular and scientific, as to the causes of these sharp changes in returns from 

 the fishery, has been indulged in for many years, no satisfying explanation has been 

 forthcoming. This is not particularly surprising, for the scientific research concerning 

 work on this species has been of desultory nature and unsuited to the solution of a 

 problem as intricate as is presented by the fluctuations in fish populations. None- 

 theless, from the fragmentary records then available, Bigelow and Welsh (1925, 

 pp. 198-199) found evidence suggesting that the mackerel, like the Norwegian herring, 

 was subject to marked inequalities in the annual success of reproduction or of survival 

 to commercial size of the various year classes, and attributed the intermittently good 

 and poor years of fishing to intermittently good and poor seasons of spawning or 

 survival. 



This hypothesis, being the most reasonable one thus far advanced, determined 

 the method of approach in the present investigation. Obviously, its pursuit required 

 two basic series of observations: (1) An estimate of changes in abundance, and (2) 

 determination of changes in age composition. Carried through a number of years, 

 these observations should provide material for measuring the relative numerical 

 strengths of year classes arising from each season's spawning, for tracing the influence 

 of the annual increments afforded by each year class and their subsequent mortality 

 on the success of the commercial fishery, and conversely for examining the influence of 

 the commercial fishery both on the reproductive success and on the mortality. 



Accordingly, after some preliminary field work in 1925 at Woods Hole and Boston, 

 Mass., in which various techniques of sampling and measuring were developed, a 

 routine program of observations was commenced at the principal mackerel fishing 

 ports. For the estimation of changes in abundance, pertinent details covering the 

 landings by mackerel vessels were recorded to form the basis for computing catch per 

 unit of fishing effort ; and for the determination of age-composition, samples of mackerel 

 were drawn daily from each of a number of the fares landed. These basic observations 

 began in 1926 and have continued to the present time. In addition, inquiries were 

 pursued into the natural history and habits of the mackerel, since more adequate 

 knowledge of these was required for interpretation of the data derived from the 

 commercial fishery. 



During the 10 years, 1926 to 1935, sufficient material has accumulated to provide 

 substantial contributions to the understanding of the life history of the mackerel, with 

 special reference to its fluctuations in abundance; and, accordingly, a series of papers, 

 of which this is the first, is to be published. 2 The present paper deals with features of 

 the early life history, with particular reference to the understanding of variations in 

 the annual replenishment of the commercial stock. It summarizes present knowledge 



1 Results, of preliminary nature, previously published are to be found in Sette, 1931, 1932, 1933, and 1934. Also see Sette and 

 Needier, 1934. 



