SCIENCE AND THE SEA FISHERIES 239 



in the south-western part of the North Sea than in the south-eastern, 

 there being a greater depth of water and a higher salinity and 

 temperature in the former region. Another interesting fact estab- 

 lished by these experiments is that the flounder when on its seaward 

 migration for spawning purposes takes no food, but utilises the 

 material stored up in its tissues for the development of its repro- 

 ductive organs, so that when the spawning period is over there is 

 a decrease in weight of from one-fifth (in the males) to two-fifths 

 (in females). The German results have been confirmed by the 

 observations of Redeke^ in the Zuyder Zee. Here no less than 

 514 flounders were marked and liberated ; of these 284, or about 

 55 per cent, were recaptured. This high percentage is due for the 

 most part to the fact that these investigations were carried out at 

 the time when the local fishery was most active. As a rule the 

 flounders marked by Redeke, hke those of the Elbe, did not return 

 to their original locality, one of the Zuyder Zee specimens wandering 

 to the Meuse and another to the Seine. The general tendency was 

 to the south-west. Up to the time these experiments were com- 

 pleted a far more satisfactory case for seasonal migration was made 

 out for the flounder than for the plaice. 



A considerable number of plaice have been marked and liberated 

 in the North and Irish Seas. The label in general use consists of 

 three parts, a bone button, an elliptical numbered brass disc, and a 

 silver wire, and is af&xed to the fish in the following manner : — 



The fish is pierced through the fleshy part of the body, midway 

 between the head and the tail, by means of a steel needle, the 

 perforation being a little below the base of the dorsal fin ; the 

 wire bearing the bone button at one end is then pushed through 

 the fish, the label is put on and a small loop made by means of 

 round-nosed pliers and turned down on the label. The whole 

 operation which sounds rather alarming, takes less than a minute ; 

 no blood is drawn and the fish apparently suffers no pain or incon- 

 venience. The marked fish are kept for a time in tanks on board 

 the investigating steamer, until they are seen to be in a thoroughly 

 healthy condition. The mortality among marked fish prior to 

 liberation is extremely small, certainly much less than i per cent. 

 The co-operation of the fishermen, which is essential to the success 

 of the experiments, is secured by offering a small reward for the 

 return of a marked fish together with particulars of the date and 

 place of recapture. As a general rule the fishermen return the 

 marked fish willingly, but in some cases they are reluctant to do 



' Rapport over onderzoskingen betrefjende de visscherij in de Zuiderzee ingest, i.d.j. 

 1905 en 1906. H. C. Redeke. S'-Gravenhage (1907) Bijlage III, m. pi. 36 en i, 

 Kaartje. 



