RAPPORTS, XIII C 4 : MASTERMAN — 22 — 



our information. Abundant evidence is to hand to indicate the comparatively deep water 

 in the central part of the Flemish Bight as an intense spawning ground for the plaice, 

 and it now seems necessary that in the light of this fact, a thorough survey of this 

 area should be made. 



(a) Intensive plankton observations should be taken at close intervals over the grounds 

 and the area off Flamborough Head, as indicated in this Report, to determine the exact 

 spawning areas and duration of spawning with special regard to the stage of development 

 of the eggs. 



(b) Floating-bottle experiments on a large scale should be instituted for determination 

 of the direction and extent of the pelagic drift to the littoral region. 



(c) Further a large no. of length, weight, age and sex-determinations should be made, 

 from samples extending over the whole area covered by the English and Dutch sailing 

 trawlers. The extensive ichthyometric data cover this area to a large extent but they 

 require to be supplemented by age and sex-determinations of the same nature as those 

 already prosecuted further north. Especially, research under these three heads would be 

 calculated to throw light upon the possible existence of a small race of plaice inhabi- 

 ting the southern portion of the North Sea and its exact relationship to the northern race. 



(4) In the previous Report several recommendations with regard to statistics were 

 made. Sufficient time has not yet elapsed for these to come into force but it is known 

 that in various directions steps have been taken to give effect to them, as far as is 

 possible. . , 



At present there are large accumulations of statistical and other data (such as the 

 returns of the "Huxley") extending over six or seven years which will require digestion 

 and tabulation, in various directions for specific questions. As each report upon this 

 material is published and the results are fitted into their proper place with the knowledge 

 already attained a clear conception will be gradually obtained of the natural phenomena 

 regulating the occurrence of pleuronectids in the North Sea and the effect of man's 

 operations. 



Explanation of chart. 



Black lines enclose areas denoted by Lee as containing the most important spaw- 

 ning grounds. 



In the Flemish Bight the space enclosed constitutes her "H" and "M" areas. 

 "Report on Lowestoft Sailing Trawler Records", 2nd. Report Part II. North Sea In- 

 vestigations (Southern Area) p. 104 and chart. 



The Areas inclosed 5W. and E. of the Dogger consist of her areas X. I. J. N. Report 

 on Grimsby Steam Trawler Records, 1Q04— 7 (now in the press) in which is stated that 

 Area X 1 Flamborough Off) as a spawning area and that both maturing and spawning 

 plaice are present regularly in the central areas J. N. and I. in which the depths are all 

 over 20 fathoms. Miss Lee adds that the Southern Area however shows more definite 

 accumulations of spawning plaice than any of the areas in the central region. 



The broken lines demarcate those areas which Hefford ("The Proportionate Dis- 

 tribution of the Sexes of Plaice in the North Sea", Rapp. et Proc. Verbaux, Vol. XI 

 p. 135) found contained the chief spawning grounds in this part of the North Sea. The 



