486 SOME RESULTS OF THE TXTEKNATIOXAL FISHERY INVESTIGATIONS. 



the connexion of the cod fisheries with the hydrographic changes. In 

 the winter of 1902-3 the Atlantic stream in the Norwegian sea 

 attained its niaxinmm much later than usual. That is, the stream 

 had a greater volume than usual in this winter, and much more warm 

 Atlantic water entered the northern ocean than in previous years. 

 Many climatic phenomena accompanied this greater accumulation of 

 warm water; the ice border everywhere receded to the north and east. 

 Barometric depressions and cyclonic storms were more numerous than 

 usual, and the weather was wild and stormy. Biological phenomena 

 were also occasioned ; Atlantic plankton was found as far north as 

 70° N., even among the drifting ice floes near Jan Mayen. The spawn- 

 ing period of the cod was greatly postponed, and the Lofoten cod 

 fishery (which depends on spawning fish) was delayed for two months, 

 and was a partial failure. The winter herring fisheries at Bergen and 

 in the Skagerak also failed. 



Quite recently too Schmidt has made some interesting observations 

 on the cod fisheries off the coasts of Iceland. The island is surrounded 

 by cold Arctic water, but on the south the Atlantic stream approaches 

 it and flows, as the Irminger Current, along the north-west coasts. The 

 cod spawns at the south of Iceland in the border region of the warm 

 Atlantic stream and the cold littoral water, and the eggs are only found 

 where the temperature of the water is over 5° C. Having spawned, the 

 cod go west and north-west, following the Atlantic stream, and in 

 the summer there is a general movement of cod, herring, and fish fry 

 along the north and east coasts of Iceland; the fisheries take the same 

 course, always in the border region of the Atlantic and Arctic waters. 



More instances of hydrographic-biological phenomena might be quoted 

 from the International publications, but we have noticed the more 

 striking cases. The question why this connexion exists must be left 

 for future investigation, and will certainly only be solved by very 

 laborious researches. One wonders that the minute differences of 

 salinity such as exist in tlie sea, and the comparatively small temperature 

 differences, should affect so notably the migrations of fishes. It is 

 perhaps a possible explanation that it is the food of the fishes that is 

 affected in some such manner as we have discussed in relation to 

 the varying abundance of diatoms in the plankton, but it is also 

 probable that the metabolic processes of the fishes themselves are affected 

 by even these small variations in the watery medium in which they live. 

 After all, climatic differences affecting ourselves are sometimes very 

 subtle, and when expressed by the readings of meteorological instru- 

 ments are just as small as those which we have been considering. 



