of the Fish ery Board for Scotland, 199 



Table III. 



Showing the Relative Proportions of the Immature ami Mature Plaice at 

 Different Sizes, from the Northerly Portion of the North Sea. 



Sex. 



Condition of 

 Reproduc- 

 tive Organs. 



Size in Millimetres. 





260-280 



3280-300 



300-320 



320-340 



340-360 



360-380 



380-400 



400-420 



Males 



Immature 



12 



25 



23 



7 



1 



0 



0 







Mature 



9 





15 





12 



LV 



a 

 O 





Do. inpec- 

 centage 



Immature 

 Mature 



86 

 14 



83 

 17 



61 



39 



24 

 76 



8 

 92 



0 



100 



0 

 100 





Females 



Immature 



9 



21 



24 





1 



0 



; 



0 





Mature 



0 



0 



3 



3 



4 



12 





7 



Do. in per- 

 centage 



Immature 

 Mature 



100 



0 



100 



0 



89 

 11 



70 



30 



20 

 80 



0 

 100 



29 

 71 



0 

 100 



From these curves it is seen that the point of crossing lies very close to 

 320cm. (about 12'5in.). The lower limit of the mature specimens 

 begins lower than 26'Ocm. (lOin. approximately), whilst the upper limit 

 of the immature is about 37cm. (14'5in.). The range of variation does 

 not seem to be so great therefore for the northerly specimens as for the 

 southerly, but this may arise from the smaller number of specimens 

 examined. If the distance between the average sizes of the males and 

 females at maturity which was observed in the specimens from the 

 southerly North Sea — viz., 7*0cm. (about 3in.) — be utilised fcr those from 

 the northerly North Sea, then the average size, when the female plaice of 

 the latter region become ripe for the first time, is about 39 '6cm. or 

 15-5in. 



The average size at first-maturity for the male plaice of the southerly 

 North Sea was found to be about 26-0cm., a difference of 6cm., or more 

 than 2in., from that of the northerly North Sea. Whether this difference 

 means that the plaice of the latter region become mature at a later age — 

 i.e., a year later, than those of the former it is impossible at present to 

 say. It may be that they grow much faster and spawn at the same 

 average age ; but this question can only be satisfactorily determined when 

 the ages at different sizes can be ascertained. 



On the east coast of Scotland, Fulton* has investigated the sizes at 

 which the plaice becomes mature, the relative proportions of males to 

 females, and their average as well as maximum sizes, The average size 

 at first-maturity was not specially sought for, and it is consequently 

 impossible to compare his results and my own with any definiteness. 

 The limit between immaturity and maturity — i.e., the commencement of 

 maturity — is placed about 12-1 3in. This agrees exactly with what has 

 been recorded here for the females, but it has been shown that the males 

 may be mature at llin. and even lower. 



A comparison may be drawn between the average sizes at maturity of 

 the North Sea plaice and those of the Kattegat and Baltic. Petersen states 



* Fulton, T. W. : Eighth Rep., Scot. Fish. Board.??. 161,162 ; Tenth Rep., Scot. Fish, 

 Board, pp. 239 et seq. ; Twelfth Rep., Scot. Fish. Board, p. 307. 



