400 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



UTILITY OF PLANKTON INVESTIGATION. 



1. The Modern Problem Many of the older 



naturalists worked at marine plankton qualitatively, and 

 even connected the prevalence of certain organisms with 

 the prosperity of sea fisheries ; but modern instruments 

 and methods of precision, such as might be expected to 

 prove quantitatively the influence of variations in the 

 type and amount of plankton, at different seasons and 

 depths, upon the movements and abundance of fishes, 

 have only been employed of recent years, and it is still 

 too early to expect much in the way of demonstrated 

 result. 



Some data have been obtained which are full of 

 promise for the future ; but marine biologists investi- 

 gating the plankton in recent years have rightly felt that 

 their immediate duty lay in making detailed experiments 

 at different localities and seasons, and under various 

 conditions, in order to test and standardise their instru- 

 ments so as to determine the causes and understand the 

 meaning of the variations in their catches. There is 

 still much to be done in the way of obtaining agreement 

 as to the nets to be used and the methods of investigation 

 of the catches to be adopted before the results from 

 different localities can be compared. 



2. Plankton as Food of Fishes. — Many commercial 

 fishes feed upon plankton during at least some portion of 

 their life. The Loch Fyne herrings are frequently, at 

 the time of a fishery, found to have their stomachs filled 

 with Nyctiphanes, Euchaeta or Calanus. In some parts 

 of the Hebridean seas the herrings have their stomachs 

 filled with the Pteropod Limacina retroversa, and other 

 oceanic organisms which may be carried in swarms into 

 our coastal waters. Many other similar cases could be 



