REPORT ON MACKEREL INVESTIGATIONS IN 1897. 



By J. Percy Moore. 



INTRODUCTION. 



The almost unparalleled scarcity of mackerel in oiir waters during 

 tlie last decade, and the consequent loss to our fishermen, having given 

 rise to the fear of a permanent decrease in numbers of this excellent 

 fish, it has become incumbent upon the United States Fish Commission 

 to determine the cause of the decrease and, if possible, to augment 

 the supply. Similar periods of scarcity, but of shorter duration, are 

 recorded from time to time in the history of the mackerel fishery, and 

 have hitherto been followed by times of greater plenty. This well- 

 known fact should lead us to hope that the present conditions are only 

 temj^orary, but it is none the less important to determine, and if pos- 

 sible to overcome, the disturbing cause, to the end that a constant and 

 certain supply of this capricious wanderer may be had. 



Why the mackerel supply is thus subject to periodical wax and wane 

 is unknown. There are no certain data upon which to venture a solu- 

 tion 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 iu 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 ax^parent decrease due to migrations of the 

 fish from our waters to other parts of the ocean ? This view, most fre- 

 quently accepted as explaining the fact, has little to support it, and is a 

 mere guess founded on the known wandering habits of the mackerel. 



For several years past the Fish Commission has attempted to over- 

 come the deficiency by propagating the mackerel artificially. So far as 

 any practical results are concerned, the attempt has been unsuccessful. 

 Briefly stated, the difiBculties have been two, namely, the number of 

 eggs obtained has been entirely inadequate, and the proportion hatched 

 in most cases has been low. 



The present report contains a statement of the results attained in the 

 course of a brief study of this work of mackerel propagation during 

 the season of 1897. The investigation was begun in early June at 



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