358 Part III. — Twentieth Annual Report 



varies considerably, not only for ditterent seas but for difterent parts 

 of the same sea— e.g., the North Sea.* 



The sizes and ranges given, even for regions nearly similar, do not 

 always agree, and it seems to me from a re -examination of the evidence 

 that the subject deserves further investigation on a larger scale than 

 hitherto. Holt, who investigated this point by the examination of a 

 large number of plaice landed at Grimsby, came to the conclusion that 

 seventeen inches represented the average size at which female fish 

 became mature in the North Sea,t but many were found matvire at 

 fifteen inches, and one at thirteen inches. It is not clear whether all 

 the fish came from the same part of the North Sea. Holt found a male 

 ripe when it was only six inches in length, an occurrence which he says 

 is probably altogether exceptional, fifteen inches appearing to be nearer 

 the usual size at which the male becomes mature, but he says he did not 

 pay very much attention to that sex during the spawning season. Cunn- 

 ingham found that at Plymouth the female may spawn at about ten or 

 even nine inches in length, and from the investigations made at 

 Grimsby he found that the size at maturity varied very much according 

 to the region from which the fish had been taken. Among plaice taken 

 in the neighbourhood of the Brown Ridges, for example, males were 

 found mature at sizes from nine to fourteen inches, and females f]"om 

 eleven to sixteen inches, and some caught ofl: the Hook of Holland had 

 a similar range of sizes. Among plaice taken about 15 miles north of 

 the island of Nordeney the limits were considerably higher, from 

 eleven to seventeen inches for the males, and while one female was 

 mature at eleven inches, 92 were immature between ten and fourteen 

 inches, one mature at eighteen and two at twenty inches. Among plaice 

 from the Leman Shoals, which is somewhat north of the Brown Ridges, 

 the limits were found to be mvich higher than at the latter place, 

 mature females ranging from thirteen to eighteen inches, corresponding 

 with the observations of Mr. Holt. Among others caught forty to 

 forty-five miles E.S.E. of Lowestoft, males were mature from eleven lo 

 sixteen inches, and females from twelve to eighteen inclies. In all 

 these cases the higher limit of the immature specimens in the same 

 collections, was usually about three inches or four inches above the lowei' 

 limit of the mature specimens. 



Kyle's inquiry places the average of first- maturity of the plaice in the 

 southern part of the North Sea between thirteen and fourteen inches for 

 the female and between ten and eleven inches for the male ; and for the 

 northern part of the North Sea at about fifteen inches for the female 

 and eleven or twelve inches for tlie male. Thirteen inches was fixed by 

 me as the lower limit of mature males, and about fifteen inches as the 

 lower limit for mature females. 



It will be seen from the curve of measurements of the plaice taken in 

 Aberdeen Bay on 6th November (PI. XIV.) that the males of Group IV., 

 which apparently range in size fi'om ten inches to fourteen inches, with 

 an average size of 1 2|- inches, and are about three years and six months 

 old, are mature. It might be held that many of these males may have 

 spawned in the previous spring when three years old, but in the group 

 as it is in November the curtailment of growth is not at all marked, 

 and this is not likely to occur until the reproductive elements have 

 matured. On the assumjDtion that the growth in summer amounts on 



* Holt, Pruc. lloif. JJnh. S(X\, ./oiirii. Mar. Jiiol. Asi<vr. ; Fulton, Eiijkth Ann. Re[i. 

 Fishery Boaid for Scotland, iii., p. 163, Tenth, ibid., 240; Cunningham, Jonrn. Mar. 

 Biol. Assoc, iv., 16, 100 ; Kyle, Seventeenth Ann. Report Flsheri/ Board for Seof., iii., 190; 

 Petersen, /or. cit. 



t Ihkh, ii.,374. 



