MACKERELS, HORSE-MACKERELS, ALLIED FORMS 133 



similarly two-year-old mackerel are thought to attain to about 

 8 in., and three-year-old fish to 1 1 in., which would be the 

 arrival at sexual maturity. 



Undoubtedly, however, the most interesting matter in the 

 life-history of mackerel is the extent and direction of their 

 migrations. That these great movements of the shoals will 

 have less mystery for us as time goes on there can be little 

 doubt, for already, thanks to the indefatigable researches of 

 Messrs. Allen and Garstang and others in this country, and 

 of Professor Sars in Norway, we are in a position at least to 

 qualify considerably the confused accounts of earlier writers. 

 Modern enquiry has, at least, had one result inseparable from 

 scientific research. It has compelled us to interpret the pos- 

 sible movements and relations of the great mackerel shoals 

 with all reservation, the confident and circumstantial accounts 

 published more than twenty years ago no longer finding 

 support among the more cautious zoologists of to-day. The 

 subject is immensely interesting, and has occupied many sheets 

 of the Journal of the Marine Biological Association and other 

 ichthyological publications. Only the barest possible summary 

 can here be attempted. Briefly, then, it seems that the mackerel 

 appears yearly off the west coast of France (Douarnenez) at 

 the end of January, somewhat earlier in the year than with us. 

 Early in April the Atlantic shoals of larger mackerel approach 

 nearer to the south-west headlands of Ireland, and in May they 

 are caught in quantities in Cornwall and Devon, the fishery 

 lasting throughout June and July, and falling off in August. 

 In October there is an autumn revival ; but by the following 

 month the main body of the fish has practically forsaken the 

 coasts of Great Britain, though a few are netted in the south- 

 west of Ireland up to Christmas. It would seem that the 

 surface temperature of the inshore waters is the main deter- 

 mining factor in these coastal movements ; and Matthias Dunn 

 in Cornwall, and several eminent ichthyologists in America, 

 agree on 45° F. as the lowest temperature agreeable to the 



