324 FOUNDEHS OF OCEANOGRAPHY 



under different conditions. The work will have to be done 

 in each great area, such as the North Sea, the English 

 Channel, and the Irish Sea, independently. This is a necessary 

 investigation, both biological and physical, which lies before 

 the oceanographers of the future, upon the results of which 

 the future preservation and further cultivation of our national 

 sea-fisheries may depend. 



It has been shown by Johnstone and others that the 

 common edible animals of the shore may exist in such 

 abundance that an area of the sea may be more productive 

 of food for man than a similar area of pastm'e or crops 

 on land. A Lancashire mussel-bed has been shown to have 

 as many as 16,000 young mussels per square foot, and it is 

 estimated that in the shallow waters of Liverpool Bay there 

 are from 20 to 200 animals of sizes varying from an 

 amphipod to a plaice on each square metre of the bottom. 

 Shelf ord, in America, states that 4 square feet of the sea will 

 support one human life. 



From these and similar data which can be readily obtained, 

 it is not difficult to calculate totals by estimating the 

 number of square yards in areas of similar character between 

 tide-marks or in shallow water. And from weighings of 

 samples some approximation to the number of tons of 

 available food may be computed. But one must not go 

 too far. Let all the figures be based upon actual observa- 

 tion. Imagination is necessary in science, but in calculating 

 a population of even a very limited area it is best to believe 

 only what one can see and measure. 



Countings and weighings, however, do not give us all 

 the information we need. It is something to know even 

 approximately the number of millions of animals on a mile 

 of shore and the number of millions of tons of possible food 

 in a sea-area, but that is not sufficient. All food-fishes are 

 not equally nourishing to man, and all plankton and bottom 

 invertebrata are not equally nourishing to a fish. At this 

 point the biologist requires the assistance of the physiologist 



