238 THE SEA FISHERIES 



the approach ot sexual maturity forces them to make the long 

 migration to their native place. 



Flounder marking experiments have been carried on in the 

 Baltic mainly by German and Dutch observers. Off the island of 

 Bornholm there is a fishing ground which in winter and spring is 

 stocked with flounders, either spawning or about to spawn. The 

 male fish predominates largely, forming about 70 per cent of the 

 catch. The male flounder, like the plaice, is appreciably smaller 

 than the female, the smallest ripe male observed was only 5| in. in 

 length, the smallest female being 6| in. On this Bornholm ground 

 770 marked flounders were liberated by Strodtmann^ in February 

 and May, 1905. During the following summer nearly 5 per cent 

 of these fish were recaptured, and in all cases near the coast in 

 shallow water. The records show that the shoreward migration 

 only commenced at the close of the spawning season, and then 

 proceeded with considerable rapidity. One flounder travelled 

 40 miles in 13 days, another 70 miles in 18 days, that is on the 

 average from 3 to 4 mUes a day. It was not found possible to 

 establish a migration along the coast during the summer months. 

 In the Baltic, therefore, the flounder migrates from the rivers and 

 estuaries in winter to the open sea, and in the late spring and 

 summer makes the return journey. During its stay in the sea it 

 spawns, and the larvae are hatched there. In the winter the young 

 and immature fish are met in the coastal waters. On the North 

 Sea coast the complement to the above experiment was undertaken 

 by Ehrenbaum,'' who at the end of the autumn flounder fishery in 

 the Elbe in 1905 and 1906 marked altogether 753 fish ; and of 

 these 35 were recaptured in the Elbe and 29 beyond it, together 

 about 8^ per cent. 



Of the sixty-five fish returned, four were recaptured from other 

 rivers than the Elbe, namely two irom the Ems and two from the 

 Weser. From this it is suggested that the flounder, unlike the 

 salmon, does not confine itself to one river. This may be due to 

 the fact that the river is the native place of the salmon, whereas 

 the flounder is hatched in the sea. Some of the other flounders, 

 which were recaptured in coastal waters, had wandered so far from 

 the mouth of the Elbe as to render it highly improbable that they 

 would have re-entered that river. Fourteen were recaptured off 

 the coast of Holland, indicating a tendency for a general migration 

 in a westerly direction. Probably the conditions for the spawning 

 of the flounder, as well as for the plaice, are far more favourable 



1 Zur Biologie der Ostseefische von S. Strodtmann. Mitteilungen des Deutschen 

 See Fisherei Vereins. Bd. 22, 1906. ji \ ,„., 



» Versuche mit gezeichneten Flundern oder Elbbutt {Plettronectes flesus) von 

 E. Ehrenbaum. Mitteilungen des Deutschen See Fischerei Vereins. Bd. 23, i907' 



