RECENT HYDROBIOLOGICAL INVESTIGATIONS 619 



date of their appearance at Lofoten. It would follow from 

 this argument that a season characterised by an unusually large 

 number of eggs in the sea would be followed by a season, 

 some seven years later, during which an unusually large num- 

 ber of adult cod would be caught. There are no determina- 

 tions of the number of cod-eggs per unit of sea surface, but 

 the mass of roe taken in the course of a fishery is a rough 

 measure of the fecundity of the fishes, for only a proportion of 

 all the cod actually present on the fishing-grounds are caught 

 by the fishermen. It is interesting then to note that, on the 

 whole, curves showing the quantity of roe taken and the total 

 numbers of cod taken can be superposed so that they show 

 similar phases, if the curve of fish taken is pushed forward 

 seven years in advance of the curve of roe taken. There are 

 obviously many sources of error in such a comparison, but the 

 relation is distinctly indicated by the statistics available. 



Summary and Conclusions 



Certain conclusions appear to emerge from a consideration 

 of the data referring to the fisheries and harvests of Norway, 

 when compared with the records of sea-temperatures and 

 salinities in extreme northern seas. The air-temperatures on the 

 land, and other climatic phenomena ; phenological events, such 

 as the dates of flowering of certain plants; the relative growth 

 of certain trees ; and the productivity of some harvest crops, — 

 are directly related to certain physical conditions in the sea. 

 A strong Gulf Stream flow in northern latitudes is to be 

 associated with mild and boisterous weather; with high sea- 

 temperatures, and a relative freedom from ice in Polar waters; 

 and also with an earlier seed-time, and a more abundant harvest 

 than usual. Further, the flooding of northern seas with the 

 relatively warm water of the Gulf Stream drift is a somewhat 

 tardy process : this water streams to the north-east very slowly, 

 so that it can be foretold a year or two in advance what the 

 conditions of the sea off the coasts of Scandinavia are likely 

 to be. The effect of the sea-temperature on the fisheries appears 

 to be the opposite to that produced in the case of the harvests. 

 In the latter case a strong Gulf Stream flow leads to a good 

 harvest ; but a strong Gulf Stream flow is apparently produc- 

 tive of a bad fishery. This applies not only to the Lofoten 



