SCIENCE AND THE SEA FISHERIES 231 



because in the case of the Copepoda and the moUusca the car- 

 bohydrates must be to some extent contained in the ahmentary 

 canal ; the shells and carapaces ot the molluscs and Crustacea are 

 not included . For albumen the Copepoda closely rese mble the oyster 

 and mussel, while for fat, Copepoda, crabs, lobsters, oysters and 

 mussels all come close together. 



Since it is possible to estimate the amount ot plankton produced 

 for a given area of the sea by the volumetric or gravimetric deter- 

 minations of the catches of the Hensen vertical plankton net, and 

 since it is also possible to express this plankton in terms of food- 

 stuffs, we can institute a comparison between the productivity of 

 the sea and the land. According to Hensen the total annual pro- 

 duction of plankton per square metre of the Baltic is 150 grams, 

 while Biebahn and Rodewald estimate the productivity of cultivated 

 land as equivalent to 179 grms. of dry organic substance per annum. 

 The fertility of the sea is according to this estimate about 20 per 

 cent below that of cultivated land. But when one considers what 

 an enormous extent of land is incapable of cultivation it may be 

 reasonable to assume that the produce of the sea in organic sub- 

 stance compares favourably with the land. The yield of the sea 

 may be vastly different in different latitudes. On land it is well 

 known that the tropics produce far more luxuriant vegetation than 

 the frigid zone. He who has to force a path through the dense 

 vegetation of a primeval tropical forest, and subsequently sees the 

 stunted vegetation of Spitsbergen barely emerging from the soil, 

 is easily convinced of the contrast. 



In the sea it is exactly opposite. While it is true that there is a 

 greater variety of form and colour among marine plants and animals 

 in the tropics, there can be no question that the amount of life is 

 greatest in the colder seas. All the great fisheries of the world 

 have been prosecuted in cold and temperate seas ; the banks of 

 Newfoundland, the cod fisheries of Norway, and the great trawling 

 grounds of the North Sea are examples that will occur to everyone. 

 But the absence of fisheries in the tropics might conceivably be 

 due to the apathy, indolence and lack of courage of tropical man. 

 There is, however, definite scientific evidence that the productivity 

 of tropical seas is less than that of Arctic seas. Hensen 's method 

 has been tried in the waters of Greenland and the Mediterranean, 

 in various parts of the Atlantic Ocean by the Plankton Expedition 

 of 1889, by the author in the Bay of Bengal, and in aumerous other 

 localities ; in all cases larger hauls of marine organisms are made 

 in the cooler waters. The largest on record are those of Vanhoffen 

 in Karajak-Fiord, Greenland, while of numerous hauls made in 

 the Baltic during the years 1889-93 only one was as small as the 



