SCIENCE AND THE SEA FISHERIES 235 



the present the greatest success has been obtained with the salmon, 

 the plaice, the eel and the flounder. The marking experiments with 

 eels^ have been for the most part carried on in the Baltic by Danish 

 investigators ; those with flounders in the same sea by German 

 scientists, but salmon and plaice marking has been extensively 

 carried on in Northern Europe. The results of marking eels in the 

 Baltic prove that the migration of the adult is a seaward one, 

 since in every case the recaptured fish were taken nearer the open 

 sea. The rate of migration was about 15 kilometres per day on the 

 average, and that for consecutive periods of from 17 to 30 days. 

 In individual cases eels moved 367 kilometres in 29 days, and up 

 to 1200 kilometres in 93 days, that is 745 miles in about three 

 months. This particular eel was liberated at Tvarminne, in Finland, 

 on the 15th August, 1905, and recaptured on the east coast of 

 Jutland, near Helgenaes, on the i6th November in the same year. 



The eel marking experiments were part of an extensive investi- 

 gation into the life history of this fish, undertaken mainly with the 

 object of solving the mystery of the spawning. 



It has been known for centuries that young eels — elvers — ^move 

 up the rivers of Western Europe in spring, and large adult eels 

 move down these rivers in autumn to the sea. These large eels 

 have a silvery appearance and are known, on the Continent, at 

 any rate, as silver eels. As soon as they get to sea they are lost 

 sight of ; they disappear entirely in the North Sea and off the 

 British coasts. In the Baltic, however, there is a regular fishery 

 for these eels, which are caught in basket -like traps. The fish move 

 parallel to the coast outwards through the Sound into the North 

 Sea. Unless the traps are set with the openings in a certain direc- 

 tion no eels are caught, the path of the eels migration is, therefore, 

 in the direction of the open sea. The marking experiments referred 

 to determined the rate of progress of this seaward migration. Adult 

 eels were never observed travelling in the reverse direction, so it 

 seems extremely probable that the eel spawns once only in its life, 

 and after spawning dies in the open sea. No one has ever captured 

 a ripe female eel, and there can be little doubt that the eel spawns 

 in the sea and only in the sea. In the spring enormous swarms of 

 young eels are seen ascending the rivers of Western Europe, and 

 these eels have the external characteristics of the adult. To get 

 into lakes and ponds which are shut off from running water there 

 is no doubt the eel makes short journeys over damp soil and grass. 

 UntU recently it was quite unknown in what part of the sea the 

 eel spawned, and there was a serious gap in our knowledge between 



• See " Contributions to the Life-History of the Eel," by Johs. Schmidt. Inter- 

 national Fishery Investigations. Rapports et ProUs-Verbaux, Vol. V, pp. 137-274. 



