APPENDIX H'; REDEKE — 4 — 



of the plaice on our coast depends very closely on its mode of life and can only be 

 understood by a detailed study of the phenomena accompanying its growth. 



The plaice of our region, of the North Sea south of the 54° of latitude, has many 

 years ago been shown to be a distinct race by Holt, Cunningham, Kyle, Duncker 

 and others. This race is distinguished in general from the plaice of the northern North 

 Sea by its smaller dimensions. It was to be expected beforehand, therefore, that our 

 plaice do not pass beyond the southern part of the North Sea but remain there during 

 their whole life, in other words, that this part of the sea forms their "dweUing-place", 

 and that there must be a close connection between the habits of our plaice and 

 the special biological and physical conditions of this dwelling-place. 



So far as investigations extending over two years entitle one to form conclusions, 

 this seems actually to be the case. 

 Eggs and iarv£E As everywhere else, the plaice in our region spawns in winter. It is impossible, 



however, to state the exact limits of the spawning period as yet, especially as the 

 principal spawning time falls in diiferent months in the different years. Nevertheless, 

 most of the plaice eggs were obtained in February and March of both years and chiefly 

 in the southern part of the region under survey. We have never taken them in very 

 great quantities, however, nor have we succeeded as yet in finding very large shoals of 

 spawning plaice. It appears as if the fish do not seek out any true spawning-places, but 

 spawn their eggs more or less in scattered fashion, preferring in this the most southerly 

 part of the southern North Sea as far as the entrance to the English Channel. 



The eggs spawned here develop in the relatively warm (7° — 8°) and sahne (> 35 °/oo) 



water coming from the Channel into the North Sea and are carried slowly by the stream 



in a north north-westerly direction a considerable distance along the Dutch coast. As soon as 



they reach the bottom-stage, the larv« must consequently fall to the bottom for the 



most part in relatively deep water (25 to 35 m.) some distance from the coast (30 to 



éo miles). 



First It is generally beUeved, that the small plaice reaching the bottom in such depths and 



ottom-stages ^^ ^^^ ^^.^^_^_^ ^^^ coast niust perish, because they are never found on such grounds, even 



during their first year, and because it is considered impossible for the quite small fish 



to be able to travel actively the wide distance which divides them from the littoral zone. 



It is certain, however, that this does not quite hold for the southern North Sea, at least, in 



its eastern portion. Firstly, because we have taken (September 1904 and again in November) 



small, first year's plaice, 70 to 80 mm., in water of 30 m. depth at 50 to éo miles from the 



coast. These were doubtless born and had grown in this deep water. Secondly, the 



small plaice on our coast must certainly travel great distances, as they are found in 



quantities, for example, in the innermost parts of the Zuydersee where the plaice never 



spawn, and where no current exists which could carry them there. 



The plaice of Jn the brackish water here, the little fish do not all seem to find favourable condi- 



ihe first year ^^^^^ j-^^. ^.^^j^ growth, as they grow but slowly. 



Their average size in July amounts to about 50 mm. and only about 60 mm. at the 

 end of January. This small increase in growth may however be in part due to the fact, 

 that the largest of these plaice in their first year, i. e. of the O-group, as it is usually 

 called, find their way out of the Zuydersee towards the end of summer, and betake 



