240 THE SEA FISHERIES 



so. There is some reason for believing that off the Cumberland 

 coast some of the inshore trawlers, thinking that the experiments 

 had for their object the imposition of further restrictions on fishing, 

 did not return marked plaice caught in their nets. In the early 

 days of the investigations the labels were frequently returned 

 without the fish, and in one case the label bore unmistakable evi- 

 dence of having been in the frying pan. 



The liberation of marked plaice in various parts of the North 

 Sea was commenced in 1902, and continued each year until 1909. 

 The results of the experiments made in the years 1904 to 1908 con- 

 firm and extend the eailier experiments ; and as a result the main 

 lines of migration of the plaice in the southern part of the North 

 Sea may be regarded as established. The most marked move- 

 ments are : (i) The migration of mature fish from the north to 

 the spawning grounds in the southern part of the North Sea, where 

 they assemble in December, January and February in the neigh- 

 bourhood of Sandettie Bank and the Hinder, east and south of the 

 mouth of the Thames, and (2) the return northwards of these 

 fish during the spring and summer to the feeding grounds in the 

 central parts of the North Saa. 



The southward autumn spawning migration is taken part in by 

 young mature fish, especially males, from the nursery grounds off 

 the Dutch coast , by similar fish from the shallow water of the German 

 Bight, as well as by larger fish from the central parts of the North 

 Sea, especially from the Leman Banks and Leman Ground, and 

 the region west, south and east of the Dogger Bank. A gradual 

 movement of the larger immature plaice from the nursery gro\mds 

 of the Dutch and German coast during the early summer into 

 deeper waters to the west and north seems also to be established 

 beyond doubt, whilst the English experiments off the Danish coast 

 have confirmed the conclusions arrived at by Danish and German 

 investigators, that a similar offshore movement of the immature fish 

 takes place in summer, and further that there is a return migration 

 of these fish in the following spring to shallow inshore grounds.^ 



It seems fairly certain that smaU plaice undertake comparatively 

 short migrations, and are generally retaken at no great distances 

 from the place where they have been marked and liberated, whereas 

 plaice of larger sizes often travel very long distances in a com- 

 paratively short time. There are isolated instances of large plaice 

 having travelled from the central areas of .the North Sea to the 

 western part of the English Channel. 



'■ For a bibliography of papers on the plaice marking experiments see Report on 

 the English plaice-marking experiments, 1906-08, by G. T. Atkinson. International 

 Fishery Investigations. Fourth Report (Southern Area). Cd. 6135, London, 1912. 



