— 7 — LATER STAGES: I'LEURONECTIDS 



The steady decline noticed in the average catch of the selected Lowestoft trawlers 

 (last column) finds its counterpart in that of the total quantity of fish landed from 1903—6, 

 but the catch per diem does not form quite so close a parallel. A comparison of the 

 more recent figures will be full of interest, as illustrating how far special statistics on a 

 small scale can be taken as representative of the whole fishery. 



C. Biological. 



Sex. 



Several important Reports dealing with the sexes and sexual phenomena in the plaice 

 have appeared during the past year. Specific reference may be here made to those of 

 Wallace (2 b), Hefford (3), and Johansen (4). The first of these observers reports on 

 observations of size and stage of maturity in 13,302 plaice, in 4,107 of which the age 

 also was determined (otoliths). They represent thirty-nine separate samples which can 

 be grouped into five main regions — The Dogger Region, lying on or near a line from 

 Flamborough Head to Esbjerg; the Inner Dowsing of the Wash; the Lenian Region from 

 from Lat. 53° 30' N. to Lat. 52° 30° N. ; the Southern Bight, in the North Sea south of the 

 Lat. 52° 30° N. ; and the Western part of the English Channel. The samples were spread 

 over 1904—7 inclusive, and were taken from September to March, during which period 

 alone it is possible to distinguish the maturity and the degrees of ripeness. Of the latter 

 the author defines three stages in the female which are found sufficient for the scale of 

 the samples, namely, Ripening, Ripe and Spent. 



The results are in the first instance applied for location of spawning shoals or spaw- 

 ning grounds. This problem has already been faced in the special statistics, and it has 

 also been approached by Hefford (above) in a study of the proportionate distribution of 

 the sexes of plaice. For the present we may remark that the latter finds a high propor- 

 tionate catch of males to be characteristic of spawning grounds. Wallace accepts this 

 conclusion, and proceeds to locate spawning areas by the two criteria of (a) a high per- 

 centage of males and (b) a high proportion of mature specimens of both sexes. Judged 

 by these standards, the Flamborough Off ground is marked out as a spawning area in 

 contradistinction to the Dogger Bank further offshore. Again "the facts point to an accu- 

 mulation of spawning plaice towards the southern end of the North Sea, and it seems 

 clear that plaice do not spawn in any appreciable numbers in the Leman Region". The 

 accompanying chart shows the locus of each sample by square dots and the grounds 

 indicated (a; as spawning grounds of the plaice (black) and (b) as feeding grounds (white). 

 The Author's samples for the Outer Dowsing and Leman grounds (Nos 13—25) are 

 all included in the groups of three northern areas (A. B. C.) mentioned in the report on 

 special Lowestoft statistics, or are just to the south of the dividing line between them 

 and the intermediate groups. The southern samples (Nr. 3. 26 — 34) are all included in 

 the groups of two southern areas (H. M.) As already pointed out , Lee finds that the 

 areas H and M (black lines on chart) are frequented by spawning plaice in considerable 

 numbers, as shewn by direct evidence of the fishermen, who recorded the presence of 

 spawning individuals. Further, the maximum catch of plaice (as represented by the catch 

 per 6 hours' fishing) occurred in these areas during the winter or spawning months. As 



