68 JOHAN HJORT. M.-N. Kl. 



It will be understood that all this fry must be dependent on the 

 ocean currents, which quite mechanically must carry them away with 

 them. The question may, howev^er, be raised as to whether the currents 

 in any other manner, through the action of the temperature, their saline- 

 ness etc., have any influence on the life of the young fish. Of these 

 conditions, which, naturally, are of the greatest importance to the life 

 of the fish, very little is known. 



The person who has studied these questions with the best result, 

 Dr. C. G. Joh. Petersen, made his investigations on board the Danish 

 floating Biological Station at Fænøsund. In Chap. Ill, in describing the 

 Plankton investigations, I have stated that Petersen discovered that, 

 during the spawning time of Flounders, eggs were onh' caught in the 

 Plankton net when the current was running southwards, whilst a lasting 

 north-going current (out of the Baltic) carried off all the eggs (out to 

 the Cattegat and beyond it). When one knows that according to Pe- 

 tersens calculation, 750000000 can drift through the small sound in the 

 course of a night, one can understand that such conditions play a ver)- 

 great part. It is of ver}- great interest that Petersen concludes, on the 

 basis of his investigations, that most of the eggs of the Plaice are swept 

 through the sounds into the Cattegat, and, possibly, beyond it. By this 

 millions are lost each year, as the bulk of the young fry cannot reach the 

 coast again, and only those that save themselves by reaching the shores, 

 can survive. On our West Coast I found the eggs of the Cod drifting 

 about, many miles to the westward of the land, and it will thus be 

 understood how dependent the fry must be on the flow of the currents 

 along the coast during those months it lives its dependent pelagic life. 

 We here encounter a condition which may, possibly, have at least as 

 great an influence on our fisheries as the currents have during the in- 

 fluxions, as the fry return at some time or other to the coast as 

 mature fish. 



Mensen ' and Petersen - made attempts to discover the specific 

 weight of the eggs, and found that most of them sank in a glass filled 

 with comparatively fresh sea-water, and required water of a great amount 

 of salinenes in order to remain suspended in it On making similar ex- 

 periments, during the past Winter, with the eggs of the Cod, I arrived 



\ 



I 



1 Vierter Bericlit der Commission zur wiss. Unlers. der deutschen Meere. VII— XI Jahrg. 

 1S84. 



2 Beretning til indenrigsm. fra den danske bioL st. IV, 1893. (Report to the Minister 

 of the Interior, from the Danish Biological Station No. IV. 1893). 



i 



