PItOGItKSS IN BIOLOGICAL INQUIRIES, 192 9 1077 



to iuijiiiu'iit lilt' mackerel stock before the 1928 brood was so severely 

 reduced that yeai's of scarcity wouhl ensue. Our 11)28 (hita indicated 

 the sui'vival of a moderate number of mackerel of the 1927 brood 

 but not enou<ili to <^ive assuranct of offsettin*^ the decline in the 

 much older 1928 brood. 



As was expected, the 1929 .'iCason witnessed a continued decline 

 in the abundance of mackerel of the 1923 brood. From a catch 

 of about 24.(K)(M)0()- tisli in 1926, these declined to a catfh of about 

 12,0(K).()()() fish in 1929. 



The 1927 bi-ood contributed (udy 2,000,000 fish. Had the year's 

 l)roduction dei)ended on these two broods, the fishery would have 

 suffei-ed a severe decline. But this was prevented by the appear- 

 ance of an extraordinarily large brood resultinjr from the 1928 

 spawnin«>; season. So plentiful were mackerel of this brood that 

 even thou<ih undesirable commercially because of their small size 

 (^about •)4-p<^'i"'l each), they nevertheless made up the bulk of 

 catches durin<^ the summer and early fall. Their yield totalled 

 more than 21,000,000 mackei-el — enouofli fish to raise the total catch 

 to 44,000,000 pounds, Avhich Avas just under that of the peak* year, 

 192G, and constituted a 40 per cent increase over 1928. 



The advent of this apparently enormous brood will undoubtedy 

 have profound effects on the abundance of fish, lasting through the 

 next several years. It is the first brood that this investigation has 

 witnessed from its beginning, and the observation of its changes in 

 abundance is almost certain to constitute a distinct contribution to 

 our understanding of the changes in abundance in this fishery. As 

 early as 1928, tentative predictions on the abundance of mackerel 

 were made in advance of the season. The forecasts thus far have 

 l^roved essentially correct. But the limitations of our knowledge 

 haA'e confined these attempts to general terms and provisional 

 qualifications. 



The attaimnent of the above-indicated understanding of mackerel 

 fluctuations has resulted from the continuation of the biostatistical 

 .study of the fishery carried on jointly by the division of fishery 

 industries and scientific inquiry since 1925. The 1929 work con- 

 tinued under the direction of Oscar E. Sette, assisted by Edward ^Y. 

 Bailey. INIost of the observations of mackerel at landing ports were 

 made by Frank E. Firth. Robert A. Goffin collected valuable in- 

 formation on the fishery in the vicinity of Woods Hole and, during 

 a short period early in the season, on the landings of the deep-sea fleet 

 at Cape May, N. J. Field assistants, engaged primarily in the col- 

 lection of data on the pound-net fishery of the middle Atlantic 

 region, also collected considerable data on the lengths of mackerel 

 taken on their stations. Altogether, information was secured as to 

 date, locality, quantity, and other items on 1,430 out of a total of 

 2,S7G fares landed by the offshore fleet. Samples from 971 fares 

 were measured. These, together with 2,734 mackerel measured by 

 pound-net observers, make a total of over 37,000 length measure- 

 ments for the season. Scale samples were taken from 615 mackerel. 



2 The mimbers of fish were calculated f)om: (1) The weight of the catch, which is a 

 matter of statistical record: (!') the Iengt)i composition of the catch, which resulted from 

 cur market measurements: and (3) the re ation of weight to length, which was computed 

 Irom weight-lengtli dat.i on more than 2,000 muckerel. 



