26 



THE SCIENTIFIC AND ECONOMIC ASPECTS 



grounds. The apparent hurry in which the fish leave their 

 diurnal haunts would seem moreover to indicate a possibility 

 that the pilchard does not enter upon the process of feeding 

 to any large extent until night time, and that it is impelled 

 by hunger to travel hastily into deeper water. 



The evidence afforded by the condition of the stomach 

 contents tends in every way to support this theory. For it 

 may be stated that when hsh are dissected immediately upon 

 coming to deck, and the contents of the stomach washed out 

 into preservative, it is possible in the majority of cases to find 

 the component material having undergone no change. The 

 Copepods, in particular, are often to be found in practically 

 intact condition. 



From the above considerations generally it is possible to 

 draw the following deductions : — 



(1) That the food of the pilchard, in coastal waters, con- 

 sists very largely of plankton. 



(2) That from the food stand|)oint plankton may be 

 divided into three distinct groups. 



To the first we may ascribe those zooplankton organisms 

 which arc undoubtedly of high nutrient value, e.g., the 

 Calanoid Copepods enumerated in the tables, together with 

 certain developmental forms of the higher Crustacea, e.g.. 

 Zoeas, Caradid larvae, etc. 



To the second all phvtoplankton, with the exception per- 

 haps of the indefinable material known as " the spores of the 

 olive seaweed," together with certain Metazoa, e.g.,Oikofleura 

 dioica, invariably associated with phytoplankton in stomach 

 contents. Such material would appear to rank as food of a 

 secondary character. 



In the third division can be placed such plankton organisms 

 as Medusae, which have not yet been found to occur in stomach 

 samples. 



(3) That food material of the first group, i.e., zooplankton, 

 is prefeired to that of the second, i.e., phytoplankton, and that 

 the organisms placed in the third group are avoided, not only 

 as probably offering no nutrient value whatever, but by reason 

 of the possession of irritant or offensive organs, rendering them 

 distinctly obnoxious. 



