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APPENDIX A : PETTERSSON 



and plankton variations therein. The tendency of these changes is for the plankton of 

 the Skager Rak to assume an arctic character in spring, an atlantic in autumn. 



The periodicity of the plankton-variations is, hovirever, more pronounced in the 

 west of the North Atlantic and Norwegian Sea. Early in the year an excessive develop- 

 ment of vegetal planktonlife takes place in these parts. It is preceded by a period of 

 sterility, the winter. In the borderregion of Atlantic and Arctic water, the former being 

 richer in animal, comparatively poor in vegetal plankton, an exuberance of planktonlife 

 developes during summer, in which a few wellrepresented species of large Copepoda 

 predominate affording ample nourishment for cod, herring a. o. fish. Nor is this plankton- 

 wealth confined to the surface-layer. The layer subjacent to the Atlantic current and 

 separating it from the cold bottom-layer displayes similar characteristics. The abundance 

 of nourishment occasions the big summer fisheries ofl" the coasts of Iceland, Shetland 

 and the Faroes. 



In the following I will try to trace from an hydrographie point of view the corre- 

 spondency between the periodic and unperiodic changes in the state of the Ocean and 

 the fish migrations. 



The fish-species that predominate in the borderregion are here 

 mentioned as "North-fishes". 



The species, that inhabit the Atlantic current proper, are here men- 

 tioned as "South-fishes". 



The arctic water proper is not inhabited by food-fishes^, conse- 

 quently there are no fisheries. 



The term "South-fish" is not synonymous with tropic fish, nor does "North-fish" 

 imply arctic fish such as the arctic cod or the "Lodde". . Nor do I propose to use this 

 classification in the same sense as once Moebius and Heincke, who thus nominated fish- 

 species appearing as casual visitors to our seas, neither residing nor spawning there. 



The geographic distribution of the "South-fish" is in the temperate Atlantic. That 

 of the "North-fish" is in the Norwegian Sea and surroundings of Iceland and Fc-eroes, 

 i.e. every place where Arctic and Atlantic water comes into contact. It follows, that 

 both categories of fish are found at such places as for instance the sea around Iceland, 

 the North Sea and Skager Rak, where enter the ramifications of the Atlantic current, 

 forming a commixture with diö"erent local sorts of seawater. 



The category "North-fish" comprises many of our common food-fishes, f inst. the 

 ling, the cod, the winter-herring, the haddock a. o. The abundance of these in the 

 North Sea and on the coast-banks of Scandinavia occasions the big winter-fisheries of 

 cod, herring etc. The classification into "North-fish" and "South-fish" however is of 

 necessity a relative one. 



As already stated the "North-fish" mostly inhabit the borderregion of the Atlantic 

 water. We know, however, that the Atlantic current is subject to annual periodicity as 

 well as to unperiodic changes, the eff'ect of which is to cause shiftings in the position of 

 the borderarea. These shiftings have connection with the fish-migrations. The field of 



I Food-fish is inclusive only of such fish as is used for human nutriment. The arctic water is 

 inhabited bv a fish the "Lodde", which as food for cods, coalfishes etc. plays a part of the greatest impor- 

 tance in the economy of the seas. 



North-fishes 



and 

 South-fishes 



The 

 North-fishes 



