THE COD FISHERIES NEAR THE LOFFODEN ISLANDS. (;51 



not in a directly easterly direction, and that it is just the coast from tbe- 

 ledges of Cbristianssund to Stavanger which is visited by the spring 

 herring, can I think be explained by purely meteorological reasons, 

 among which the temperature of the sea seems to play an important part. 

 Through the indefatigable exertions of Professor Mohn, a large num- 

 ber of observations on the temperature of the sea-water near our coast, 

 talvcu at different seasons, and extending over many years, have been col- 

 lected ; and some of these observations were taken at a considerable dis- 

 tance from the coast. In the pamphlet published by him in French, in 

 1870, entitled Temiierature de la mer cntre Vlslande, VEcosse et la Noricege. 

 these observations are given, and on the accompanying maps isothermal 

 lines drawn for the different seasons give a very clear idea of the pecu- 

 liar conditions of temperature in that portion of the sea. What imme- 

 diately strikes us is the remarkable change which the isothermal lines 

 undergo during the greater portion of the year as soon as they come 

 nearer to the coast of Norway. Instead of running in-a northeasterly 

 direction, as before, they here suddenly bend toward the southeast, fol- 

 lowing more or less the coast. 



It will also be seen that the extent of coast from the ledges of Cbris- 

 tianssund to Stavanger, therefore the spring-herring district proper, is- 

 during winter distinguished above every other part of the coast by the 

 remarkably uniform temperature of the sea-water. This temperature 

 (41° F. to 430 F.) is, therefore, the very temperature which is considered 

 most favorable to the hatching of young herring. Both these favorable 

 conditions of temperature near the coast and the curving of the isother- 

 mal lines out in the ocean seem thus to furnish quite a natural expla- 

 nation of the fact that the spring-herring, although it probably lives 

 originally under more northern latitudes, always seeks this portion of 

 the coast, and not, as might be expected, the one immediately north of 

 it. From the map which shows the condition of the temperature in the 

 middle of winter, therefore at the very time when the coming in of the 

 spring-herrings begins, it will be seen that the herrings, in order to reach 

 the coast near the ledges of Trondhjem, would have to pass no less 

 than 3-4 isothermal lines, or from a temperature of 6° to one of less than 

 20 1^430 j^. to 35^'^ F.), while by taking a southeasterly direction they 

 would have the same temperature (43° F.)- nearly all the time. And as 

 it is well known that the fish are very sensible of changes of tempera- 

 ture, we seem justified in drawing the conclusion that the migrations of 

 the herring, both when approaching the coast and when leaving it, are 

 chiefly governed by the temperature, and will, therefore, naturally follow 

 the above-mentioned direction. 



By this theory, which differs very much both from the older theories 

 and from more recent ones, e.f/., that of Professor Nilsson, I think I am 

 able to explain in a natural manner many hitherto entirely inexplicable 

 lihenomena in connection with the spring-herring fisheries. In order 

 that I may not be misunderstood, I must state expressly that it is bj no 



