THE WESTERN MACKEREL FISHERY. 291 



however, when the sea west of Scilly was, according to the fishermen's 

 statement, teeming with mackerel, " yellow water " was commonly met 

 with on the fishing grounds. An examination of the Samples 50 to 57 

 (Plankton Table No. II), all of which were taken either adjacent to or 

 on the fishing area during the international plankton cruise May, 1907, 

 will serve to show that throughout the area covered the samples taken 

 showed a certain similarity. Phytoplankton was entirely absent and 

 the zooplankton was confined almost entirely to three or four principal 

 forms, of which Calanus finmarchicus and Pseudocalanus elongatus were 

 the most important. 



At one station, 49° 49' K x 6° 59' W. (Sample No. 52), the sea was 

 considered to be of a decidedly yellow tint, according to the statement 

 of Mr. D. J. Matthews, the leader of the expedition, and an analysis of 

 the very bulky sample showed that it was composed almost entirely 

 of the two species mentioned above, in almost equal abundance. 



The possible inferences which may be drawn, therefore, from the con- 

 sideration of the foregoing observations can be briefly summed up as 

 follows : — 



That in the "stinking water" sample, phytoplankton was in excess of 

 zooplankton, but that there was no evidence to show from whence 

 colour or smell were derived, beyond evidence of a negative character, 

 which would tend to suggest that the smell did not arise from the con- 

 dition of plankton. This suggestion is based upon the fact of an 

 almost equal quantity of phytoplankton occurring in the case of the 

 " green water " sample formerly referred to, " green water," according 

 to the fishermen's statement, being invariably free from smell. The 

 evidence offered by the analyses of " blue " and " green water " samples 

 would suggest that the plankton taken in such water was of a type 

 comprising a fair number of species in which, in the present examples, 

 zooplankton was in excess of phytoplankton. From lack of observa- 

 tions, however, it cannot be suggested that this is always the case. 



Finally, with regard to "yellow water," the somewhat conflicting 

 opinions expressed by fishermen as to the causes which give rise to the 

 colour, already explained, would suggest that the yellow tint is ac- 

 counted for either by the presence of excrement arising from densely 

 shoaling fish or from the presence in large numbers of certain Cope- 

 pods. In view of the fact that several fishermen declare that light 

 catches of mackerel may be taken in " yellow water," and the evidence 

 offered by the analyses of certain plankton samples, it would appear to 

 be more probable that the coloration arose from the latter cause. 

 Were this view adopted, moreover, it would be strictly in accordance 

 with the theory already discussed, of mackerel being abundant where 

 food is plentiful. 



