CAUSES OF IMPOVERISHMENT 57 



volume of sea ; a limit is therefore set to the number 

 of fish in that volume of water. Professor Hensen 

 and Professor Brandt, of Kiel, have shown that a 

 square metre of the Baltic produces an average of 

 1 50 grammes of dry organic material in the shape of 

 diatoms, copepods, and other floating organisms. A 

 similar area of land produces 180 grammes of ultimate 

 food-substance. The productivity of the sea is judged 

 on this basis to be about 20 per cent, less than that of 

 the land. The actual amount is of less importance 

 than the consequences it entails. If the methods of 

 fishing are more destructive of one species than 

 another, comparatively worthless species may become 

 dominant in areas where they were formerly scarce, 

 and thus consume the food which should be reserved 

 for their betters. It is commonly reported that the 

 dab has tended to usurp the position formerly taken 

 by the plaice, not only in the Scottish firths, but on the 

 Dogger Bank, in the Devonshire bays, and in other 

 localities. Dr. Garstang, of the Marine Biological 

 Association, tells us that small plaice transplanted to 

 the Dogger Bank in 1904 grew three times as much in 

 weight as did their fellows on the coastal banks ; but 

 in the following year they grew only twice as much, 

 owing to the presence of vast quantities of small 

 haddocks, which ate the plaice's food and were never- 

 theless too small and worthless themselves to be 

 landed by the fishermen. Yet formerly the Dogger 

 teemed with large plaice and haddock. It was stated 

 to the Royal Commission in 1863 that the fishermen 

 avoided the Bank as causing gluts of fish and deprecia- 

 tion of price ; and witnesses from Yarmouth and Hull 

 assured the Commission that between two and three 

 tons of fish, chiefly haddock and plaice, were fre- 

 quently taken by smacks in a three hours' haul. As 

 small plaice are confined to the coastal banks, and 

 large plaice are now scarce, it follows that the great 



