88 THE COMMERCIAL SEA FISHES OF 



The number of days these intervals take are generally the 

 same in different years. 



In the spring the average size of the mackerel captured 

 off the English coasts is smaller than it becomes during 

 the autumn, owing to some of the shoals being entirely or 

 partly composed of young fish. Their course appears to 

 be very erratic, rising to the surface and approaching the 

 shore, or remaining at the bottom in deep water. But as 

 the summer advances and their food enters sandy bays, 

 these fish follow and are exceedingly active. By the end of 

 September or October, having spawned, the old ones retire 

 to deep water, in which migration they seem to be fre- 

 quently accompanied by those which were hatched early 

 in the season. Sometimes the half-grown fish, when 

 retiring into deep water at the end of the year, seem to be 

 interrupted in their course, which causes them to remain 

 off the coast during the winter months. 



The character of the season or of the weather does not 

 appear to be the sole agent by which the migrations of 

 these fishes are ruled. But it has been remarked that a 

 particular temperature or the direction of the wind has 

 more connection with their swimming nearer to the surface 

 or deeper in the water, probably such influencing the 

 migrations of the animals of which their food is composed. 



The food upon which these fish subsist is still a subject 

 requiring investigation. In the month of March, 1882, 

 about 8 miles to sea off Mevagissey, and over 40 fathoms 

 of water, they were found to have been feeding upon a 

 shrimp-like crustacean, Thysanopoda Couehii, with which all 

 examined were found to be gorged. When the mackerel 

 midge, the young of the rock-ling, Motella, becomes abun- 

 dant, about the middle of May, these fishes congregate in 

 order to feed upon them, They prey upon members of 



