402 G. E. BULLEN. 



described by Mr. Mathias Dunn, whilst at the same time travelling by 

 almost imperceptible stages toward land ? 



Again, if it can be suggested with any degree of certainty that a 

 plankton organism snch as a caradid larva, which is considerably 

 smaller than the mysid Macropsis, is hunted by sight — b}'' a system of 

 selective feeding — it is a difficult matter to determine how small an 

 organism may be before a mackerel ceases to feed upon it with 

 discrimination. 



The present w^riter in a former paper* has shown that a marked 

 correlation appears to exist between the extent of the inshore migra- 

 tion of mackerel during the three months constituting the more 

 important period of the drift-fishing season in the western part of the 

 English Channel, viz. April, May, and June, and the paucity or 

 abundance of the zooplankton occurring in the same area. 



These observations, considered collectively, would tend to show that 

 mackerel prefer an animal to a vegetable diet, and that it is probable, 

 with a thorough understanding of the seasonal changes occurring in 

 the pelagic plankton of the area under consideration, it may be 

 demonstrated that shoaling mackerel frequent, in greater numbers, 

 those areas supporting a food supply most suited to their taste. There 

 is considerable evidence, moreover, in support of a theory that shoals 

 of mackerel, when entering swarms of wholesome planktonic organisms, 

 feed ravenously upon them while they last, whilst refraining from food 

 to a great extent when swimming in water containing, what we may 

 suppose to be, organisms of a distasteful character. It naturally follows 

 that in years when the coastal waters support in greater proportion 

 food of an inferior type, the extent of the inshore migration of mackerel 

 is largely retarded. 



The question naturally arises — Can this condition be traced to the 

 fish's own capability of discrimination in question of food ? Can it also 

 be urged that if mackerel are capable of hunting, presumably by sight, 

 the larger forms of the zooplankton, they are also able to discern 

 when in sufficient numbers dense shoals of the more minute forms such 

 as the copepod Calanv.s Jinmarchicus Gunnier and others, thereby still 

 exercising a system of selective feeding, though in this case in a more 

 expansive sense, viz. the obtaining of large mouthfuls of suitable 

 plankton by a selection of the type of water supporting such prey, when- 

 ever possible. 



To summarize briefly the deductions which may be drawn from a 

 consideration of the above observations, it may be stated — 



* Op. cit., p. 27S and onward. 



