FISHES AND MANKIND 407 



srrowth-rate and the available food supply, as well as an in- 

 vestisation of the migrations of the shoals of adult and young 

 fish, and so on. Further, in order to study the life-history ot a 

 particular fish, it is necessary to study its environment, and 

 fishery research must include the study of the plaiikton food of 

 the pelagic fishes, as well as the bottom-living invertebrates 

 forming the food of the demersal fishes. This in turn ln^■olves 

 the study of the minute vegetable and inorganic constituents ot 

 the diet of the plankton and the invertebrates of the sea bottom, 

 and the lines of research must be further broadened out to 

 include a study of the physical nature of the sea-floor, the 

 movements of the tides, the currents, the temperature and 

 salinity of the water; in fact, the general physics and chemistry 

 of the sea. In addition to the biological and hydrographical 

 investigations, the collection of statistics forms another important 

 branch of inquiry. Records of the quantities and sizes of the 

 different species landed at various ports by vessels employing 

 difTerent kinds of fishing gear must be accurately kept over long 

 periods, and numerous measurements of individual fishes mac^e 

 at sea, for it is only by methods of this nature that it is possible 

 to obtain some idea of the stocks of fish in the sea and the 

 reasons for the fluctuations in their composition. 



While at sea the fishery investigator is kept constantly 

 employed in measuring fish, obtaining otoliths and scales from 

 selected specimens in order that their age may be ascertained, 

 marking fish with metal discs for the purpose of studying their 

 movements, collecting samples of the sea bottom and of the 

 surface plankton, making observations of the temperature and 

 salinity, and of the chemical constituents of the water at various 

 depths, collecting eggs and larvae, and releasing special driit 

 bottles which, when subsequently recovered, serve f measure 

 the movements of the water under the influence of tides and 

 currents. Back in the laboratory, the water samples are 

 analysed, the physical and chemical data tabulated, the 

 plankton and bottom samples studied with the lens and 

 microscope, the scales and otoliths read, and the thousand and 

 one tasks connected with fishery research are constantly being 

 carried out. Each specialist working on his own particular 

 subject contributes his quota to the solution of the general 

 problems involved. "What, then, are these general Problems? 

 writes Dr. Russell in an account of the work of the laboratory 

 at Lowestoft. "Apart from the general acquisition of knowledge, 

 which has a remarkable way of turning out in the long run to 



