270 FOUNDERS OF OCEANOGRAPHY 



There is the scientific interest and there is the practical 

 utihty — the interest, for example, of tracing a particular 

 swarm of a Copepod like Calanus, and of making out why it 

 is where it is at a particular time, tracing it back to its place 

 of origin, finding that it has come with a particular body of 

 water, and perhaps that it is feeding upon a particular 

 assemblage of Diatoms ; endeavouring to give a scientific 

 explanation of every stage in its progress. Then there is the 

 utility — the demonstration that the migration of the Calanus 

 has determined the presence of a shoal of herrings or mackerel 

 that are feeding upon it, and so have been brought within the 

 range of the fisherman and have constituted a commercial 

 fishery. 



We have evidence that pelagic fish which congregate in 

 shoals, such as herring and mackerel, feed upon the Crus- 

 tacea of the plankton, and especially upon Copepoda. A 

 few years ago, when the summer herring fishery off the south 

 end of the Isle of Man was unusually near the land, the 

 fishermen found large red patches in the sea where the fish 

 were specially abundant. Some of the red stuff, brought 

 ashore by the men, was examined at the Port Erin Laboratory 

 and found to be swarms of the Copepod Temora longicornis 

 (Plate XXIII) ; and the stomachs of the herring caught at the 

 same time were engorged with the same organism. It is not 

 possible to doubt that during these weeks of the herring fishery 

 in the Irish Sea the fish were feeding mainly upon this species 

 of Copepod. Some years ago, Dr. E. J. Allen and Mr. G. E. 

 Bullen pubHshed some interesting observations, from the 

 Plymouth Marine Laboratory, demonstrating the connection 

 between mackerel and Copepoda and sunshine in the Enghsh 

 Channel ; and Farran states that in the spring fishery on the 

 West of Ireland the food of the mackerel is mainly composed 

 of Calanus. 



Then, again, at the height of the summer mackerel fishery 

 in the Hebrides, in 1913, we found the fish feeding upon the 

 Copepod Calanus finmarchicus (Plate XXIV, Figs. 1 and 2), 



