president's address. 29 



waters has become smaller, although the total number of plaice landed 

 had continued to increase up to the year of the outbreak of war. Since 

 then, from 1914 to 1919, there has of necessity been what may be 

 described as the most gigantic experiment ever seen in the closing of 

 extensive fishing grounds. It is still too early to say with any certainty 

 exactly what the results of that experiment have been, although some 

 indications of an increase of the fish population in certain areas have 

 been recorded. For example, the Danes, A. C. Johansen and Kirstine 

 Smith, find that large plaice landed in Denmark are now more abun- 

 dant, and they attribute this to a reversal of the pre-war tendency, 

 due to less intensive fishing. But Dr. James Johnstone has pointed out 

 that there is some evidence of a natural periodicity in abundance of such 

 fish and that the results noticed may represent phases in a cyclic change. 

 If the periodicity noted in Liverpool Bay=' holds good for other 

 grounds it will be necessary in any comparison of pre-war and post- 

 war statistics to take this natural variation in abundance into very 

 careful consideration. 



In the application of oceanographic investigations to sea-fisheries 

 problems, one ultimate aim, whether frankly admitted or not, must 

 be to obtain some kind of a rough approximation to a census or valua- 

 tion of the sea — of the fishes that form the food of man, of the lower 

 animals of the sea-bottom on which many of the fishes feed, and of 

 the planktonic contents of the upper waters which form the ultimate 

 organised food of the sea — and many attempts have been made in 

 different ways to attain the desired end. 



Our knowledge of the number of animals living in different regions 

 of the sea is for the most part relative only. "We know that one haul 

 of the dredge is larger than another, or that one locality seems richer 

 than another, but we have very little information as to the actual 

 numbers of any kind of animal per square foot or per acre in the sea. 

 Hensen, as we have seen, attempted to estimate the number of food- 

 fishes in the North Sea from the number of their eggs caught in a 

 comparatively small series of hauls of the tow-net, but the data were 

 probably quite insufficient and the conclusions may be erroneous. It 

 is an interesting speculation to which we cannot attach any economic 

 importance. Heincke says of it : ' This method appears theoretically 

 feasible, but presents in practice so many serious difficulties that no 

 positive results of real value have as yet been obtained.' 



All biologists must agree that to determine even approximately the 

 number of individuals of any particular species living in a known area 

 is a contribution to knowledge which may be of great economic value 



" See Johnstone, Rfport Lanes. Sea-Fish Lub. for 1917, p. 60; and Daniel, 

 Report for 1919, p. 51. 



