28 KtPUKT ON THE PKKSENT iSTATE OF KNOWLEDGE 



render it unlikely that they had made any extended migration along the 

 Irish and Scottish coasts. 



There is, however, obviously a migration through the English Channel 

 into the North Sea. Whilst mackerel are at the mouth of the Channel 

 in ]\Iarch few fish are taken either in its eastern portion or in the 

 southern part of the North Sea before the end of May or the beginning 

 of June. In the autumn, on the other hand, the large fishery in the 

 southern part of the North Sea seems to be due to the movement of 

 the fish towards the Straits of Dover, on their passage back to the 

 English Channel. The mackerel taken on the south coast of England 

 in December, January, and February are possibly, as suggested above, 

 the fish which have emigrated from the North Sea. In the present 

 state of our knowledge of the subject this is, however, a mere specula- 

 tion. An examination of the Board of Trade statistics from 1886 to 

 1895 does not show any constant relation between the number of 

 mackerel landed on the south coast of England in December and 

 January, and the success or failure of the previous autumn fishery 

 on the east coast. 



There is a certain amount of evidence that mackerel, when not at 

 the surface near the coasts, may be present in deeper water not far off". 

 This evidence has already been referred to in previous parts of this 

 Eeport. In the first place there is the fact mentioned by Green, that 

 in certain bays on the west coast of Ireland the large spring mackerel 

 are captured close to the shore two or three weeks before the larger 

 boats working in the ofting, where the water is 40 to 80 fathoms deep, 

 are able to obtain any. These early in-shore fish must have travelled in 

 towards the coast in the deeper layers of water. There is also the 

 record by Marion, that at the beginning of March, 1891, after a strong 

 mistral^ large numbers of mackerel were taken by the trawls of the 

 " bateaux boeufs," fishing six miles from shore off Cape Couronne, in 

 depths of 100 to 150 metres. It is true that in this case the objection 

 may be raised that the fish might have been captured in upper layers 

 whilst the net was being drawn to the surface, but this does not appear 

 to be a very likely explanation of the catch. Mr. Holt states that he 

 has taken mackerel in the trawl in the North Sea, after heavy weather, 

 and the Plymouth trawl fishermen say that they also obtain them under 

 like circumstances. 



Finally, we have the records of mackerel, but little digested, taken 

 from the stomachs of cod on the American coast some time before 

 the appearance of the schools at the surface. 



If the mackerel, when away from the coast, retire to deeper water, 

 where the temperature is more suitable to them, it becomes interesting 

 to inquire where they would find such a temperature. The series of 



