THE WESTERN MACKEREL FISHERY. 271 



plankton forms the main food of mackerel during the shoaling 

 season, and the examination of more than four hundred stomachs 

 of mackerel taken in the British Channel and extreme western 

 part of the English Channel, during the present investigations 

 (1906-7), has shown agreement with this result. As suggested 

 by several previous authors on the subject, it appears possible 

 that from a study of this food some light may be thrown upon 

 the factors which govern the fluctuations in the mackerel fishery 

 during the spring shoaling season. The object of this paper, therefore, 

 is to show, from the information and observations at our disposal, 

 whether there is a demonstrable correlation between the distribution 

 of plankton or mackerel food, and the extent of migration. It has 

 already been stated that over four hundred stomachs have been 

 examined during the present researches. These were taken in 

 1906-7 from fish caught in the Bristol Channel and in the English 

 Channel from Plymouth to west of Scilly, during the three months 

 which constitute the more important part of the spring fishery, viz. 

 April, May, and June. The result of the analyses of these stomachs 

 will be found in the Plankton and Food Tables which are appended. 

 From an examination of these tables it will be seen that on no occa- 

 sion has an instance occurred of material, other than plankton, being 

 observed in the stomachs of fish caught during the shoaling season in 

 the extreme western part of the area under consideration. In the 

 eastern part, however (see Table V), it will be seen that the plankton 

 forming the principal food was gradually supplemented, as the season 

 advanced, with young fish and adult Crystallogohius nilsoni. 



From information derived from the weekly market reports published 

 in the Fish Trades Gazette, and from statements made to me by local 

 fishermen at Plymouth and Newlyn, it would appear that, although 

 drift fishing had been carried on in the Bristol Channel and elsewhere 

 since the beginning of February until April in 1906 and 1907, the 

 catches made were irregular and comparatively small. Fishermen and 

 others agreed in stating that this was due to the fact, that there 

 appeared to be no regular shoaling at the surface during these three 

 months. 



That mackerel did occur, however, in the inshore waters at this 

 time at the surface is evinced by the fact that fair catches of hook fish 

 were made constantly during the early months of the two years, as 

 shown by the market reports, and by the writer's personal ob- 

 servations. 



Fishermen seem to be agreed that shoaling mackerel will not take a 

 bait : and a consideration of the above facts tends to suggest that in 



