REPORT OF COIMMISSIONKK OF FISH AND FISHERIES. CXXXI 



These inquiries were prompted by the great scarcity of mackerel, 

 which has now extended over a longer period than ever before in the 

 history of the fishery, and by the large mortality among the artificially- 

 hatched mackerel fry, to which reference has been made in earlier 

 reports of the Commission. The supply of mackerel, as gauged by the 

 catch, decreased markedly after 1S85, and for tlie succeeding 13 years 

 remained at a very low ebb, the average annual output being probably 

 only one-seventh that of the 10 preceding years. After referring to the 

 fact that short periods of scarcity have in the past been followed by 

 seasons of abundance, Dr. Moore states in his report : 



Why the mackerel supjily is thus subject to periodical wax and wane is unknown. 

 There are no certain data upon which to venture a solution of the problem. Are 

 their numbers depleted by disease? There is no evidence that the mackerel is 

 subject to any serious infectious disease. Is the decrease due to a period of lowered 

 fertility, of less or greater duration? Here again we lack facts. We know but 

 little to what extent the biological and physical conditions of the sea have varied, 

 nor yet how variations in these factors affect the vitality and habits of the mackerel. 

 There may have been no actual diminution in the propagating capacity of the fish, 

 but some condition peculiarly detrimental to the development of the eggs and 

 embryos may have existed, causing their consequent destruction on a large scale. 

 Has there been a real or only an apparent decrease due to migrations of the fish 

 from our waters to other parts of the ocean? This view, most frequently accepted 

 as explaining the fact, has little to support it, and is a mere guess founded on the 

 known wanderiag habits of the mackerel. 



The report cited first gives the results of studies relating to the 

 spawning time of the mackerel, the development of eggs in the ovary, 

 the characters of the ova, the process of fertilization, the vitality of the 

 milt, the changes in the egg after fertilization, and the hatching and 

 growth of the fry. The results of surface to wings and the outcome 

 of hatching experiments are then given, followed by a summary of 

 conclusions and recommendations. 



A point of practical importance in the artificial hatching of the fish 

 is that during development the specific gravity of the egg gradually 

 increases, so that, while the egg floats at the surface of the inshore 

 waters during the early stages, it sinks to a considerable depth before 

 hatching ensues. This fact was emphasized by the failure to obtain in 

 surface towings any eggs in the more advanced stages of development; 

 very few mackerel, however, were spawning in Casco Bay during the 

 progress of the work, although the region is ordinarily one of the best 

 spawning-grounds on our coast. 



As bearing on the relatively poor results attending the artificial 

 hatching of mackerel eggs, Dr. Moore conducted a number of experi- 

 ments with different hatching methods and apparatus. These indicated 

 that for the first two days of development no apparatus is superior to 

 the ordinary tidal boxes, provided their sides are smooth and the 

 screens are kept clean. Subsequently the requirements are pure water 

 of higher density, and a hatching vessel that aflbrds better circulation 

 and keeps the eggs in suspension instead of permitting them to settle 

 on the bottom among decaying organic matter. 



