272 FOUNDERS OF OCEANOGRAPHY 



in the following summer. Possibly the connection in these 

 cases is through an organism of the plankton. 



Nathansohn, Gran and others lay stress upon the import- 

 ance of vertical currents in bringing nutriment to the plank- 

 ton, and suggest that some of the irregularities may be due 

 to such up-welling currents from deeper water. The enor- 

 mous quantity of plankton over the Faroe Bank is probably 

 due to vertical currents caused by the bank facing the Gulf 

 Stream drift. It is a matter of common observation among 

 fishermen that where there are strong tidal races and swirls 

 sea-birds congregate, and are found to be feeding on small 

 fishes, and these in their turn are eating the abundant plank- 

 ton brought and nourished by the current. 



It is only a comparatively small number of different kinds 

 of organisms — both plants and animals — that make up the 

 bulk of the plankton that is of real importance to fish. One 

 can select about half a dozen species of Copepoda which 

 constitute the greater part of the summer zoo-plankton 

 suitable as food for larval or adult fishes, and about the same 

 number of generic types of Diatoms which similarly make up 

 the bulk of the available spring phyto-plankton year after 

 year. This fact gives great economic importance to the 

 attempt to determine with as much precision as possible the 

 times and conditions of occurrence of these dominant factors 

 of the plankton in an average year. An obvious further 

 extension of this investigation is an inquiry into the degree of 

 coincidence between the times of appearance in the sea of the 

 plankton organisms and of the young fish, and the possible 

 effect of any marked absence of correlation in time and 

 quantity. 



Just before the war the International Council for the 

 Exploration of the Sea arrived at the conclusion that fishery 

 investigations indicated the probability that the great periodic 

 fluctuations in the fisheries are connected with the fish larvae 

 being developed in great quantities only in certain years. 

 Consequently they advised that plankton work should be 



