— If, — LATER STAGES: PLEURONECTIDS 



southern corner of Hi-riiMto's southern area. Wafxace's samples in the intermediate area 

 between Lat. 52° 30' N. and Lat. 53° 40' N. also gave negative evidence of spawning, and 

 he concludes that in this area are chiefly feeding grounds. It will be seen that, so far 

 as they go, these results are completely in agreement. There are added to the chart the 

 loci of plankton observations by Redi:ki-: and Van Bremen during January and February, 

 1905 and 1906, and by German investigations in varions years up to 1909. The comparative 

 prevalence of plaice eggs in each haul is indicated by three sizes of circles. The large 

 circles representing over 100 plaice eggs to a square metre of surface are all confined 

 to the spawning area in the Flemish Bight. The second grade of 11 — 100 eggs per 

 square metre is found inshore from this, towards the Dutch coast, on the Flamborough 

 ground and east of Lat. 3° E. extending northwards from the Flemish Bight parallel to the 

 Dutch coast. These results may be partly explained by an absolutely greater intensity 

 of spawning in the Flemish Bight, and perhaps partly by a difference in time of spawning 

 as between the northern and southern races. 



So far, therefore, as the present observations of independent workers go, it would 

 appear that (a) there is one principal spawning ground of the plaice occupying the centre 

 of the Flemish Bight approximately from Long. 2° E. to 3° E. and from Lat. 50" 10' N. to 52° 

 30' N. This triangular area lies between Lowestoft, Ymuiden and Calais, and the boundary 

 line runs at least 15 miles from the Continental coast and a little more from the English 

 coast. On the west side it is separated from the more northerly spawning grounds by 

 the feeding grounds of the Leman Bank etc., but on the east there are some indications 

 that spawning takes place off Helder and other parts, possibly forming a more or less 

 continuous spawning area with those further north. 



At present our knowledge with regard to the northerly spawning grounds is more 

 meagre. There does not appear to be any such great spawning aggregation as in the 

 south but the grounds as outlined by Heffobd and Lee, and partly by Wallace, extend 

 as a great belt west, south and east of the Dogger over Ci and C2 areas of the inter- 

 national plaice areas, and partly into B4. The southern area includes almost the whole 

 of C3, so that practically the whole area of the North Sea between the depth of 40 to 60 

 metres is included in the spawning grounds. There are also indications that spawning 

 may extend into the shallower water up to about 30 metres. As further negative evidence 

 Johansen finds that the areas A3, A4, and shallower parts of B4 and B5 are in no sense 

 spawning grounds for the plaice and must be regarded as nurseries of immature stages. 

 These results derived from his study of the proportion of mature fish in catches landed 

 in Esbjerg market agree also with the negative results of the research vessels as regards 

 the occurrence of pelagic eggs of the plaice (see Chart). 



Intimately connected with questions of maturity and spawning grounds is that of 

 fecundity, or the no. of eggs produced by a single individual. It has been known e. g. 

 from the research of Fulton ' that in a general way the no. of eggs or fecundity increases 

 with the size of the individual. 



Franz (No. 5) has published data concerning the no. of eggs found in 45 plaice from 

 the North Sea and 11 from the Baltic, as an addition to those previously published. The 



I The comparative fecundity of sea fishes. 9th. Ann. Report: Fishery Board for Scotland for 1890. 

 Edintiurgh 1891. 



