FEEDING HABITS OF MACKEREL, 403 



(a) That not only mackerel, but herring also can exist for a reason- 

 able period of time, whilst exercising a system of nutrition by selective 

 feeding, irrespective of season. 



(h) That this system of selective feeding in mackerel and scad may 

 extend to the larger forms of the plankton. 



(c) That whilst it is impossible to determine how far the mackerel 

 is assisted in its search for food by its power of vision, there is strong 

 presumptive evidence to show that a capability for selective feeding, 

 in a wider sense, may be extended to comparatively minute organisms, 

 when they are present in suflicient numbers. 



(d) And that this capability on the part of the fish to discriminate 

 between food of a wholesome and that of a presumably unwholesome 

 nature, would cause it to seek in greatest numbers water supporting 

 the most suitable type of food, the extent of inshore migration thereby 

 being largely dependent upon the planktonic condition of the coastal 

 waters. 



(c) Finally, that there is a by no means negligible amount of evidence 

 to show that, when feeding upon the minor forms of the plankton, 

 mackerel are incapable of assimilating other larger prey — which theory, 

 if more fully established, would lend further support to the deduction 

 that there is necessity for a suitable and abundant supply of plankton 

 in the inshore waters before the shoals are induced to approach the 

 land in sufficient numbers to form a profitable fishery. 



In the preparation of this paper the writer's thanks are due to 

 Mr. Mathias Dunn and Mr. E, W. Cowley for their valuable observa- 

 tions, also to Dr. E. J. Allen for much assistance and advice. 



