72 



but the distribution of the dab points to another factor being 

 at work. 



The Northumberland plaice therefore during the years of 

 immaturity remain in or near the territorial waters, partially 

 migrating inshore and offshore according to season. They do not 

 leave the district, but the figures in detail indicate that they are 

 liable to be joined by others from deeper water. We have not 

 enquired carefully as to the age when maturity takes place. The 

 majority of the plaice marked during the summer of various years 

 ranged from 13 to 30 cm., but the most only 20 to 24 cm.. The 

 majority would therefore be of Groups II. and III., with a few 

 of IV. and V. The smallest female which migrated from the 

 district for spawning measured 29 cm., and probably belonged 

 therefore to Group IV. It was not until the following season, 

 and the second season after that of the marking, that the plaice 

 had grown sufficiently to become mature. Such measured 30 

 to 34 cm. (females), and 33 to 45 cm. (males). The examples 

 are not numerous, but they point to maturity arriving when the 

 fish are in Groups IV. and VI. Wallace found from an examina- 

 tion of the plaice of the Channel and the southern North Sea up 

 to and including the Dogger Bank that the age at maturity 

 increased with latitude, that of the Channel being three years 

 (males) and four years (females), southern North Sea five years 

 (males) and six years (females), and of the north-east part of the 

 Dogger six years (males) and seven years (females). At the time 

 of spawning the Northumberland school would probably range 

 from four to six years, and are thus more like the plaice of the 

 southern North Sea. It may be found that the plaice of the 

 northern current present a similar succession as that shown by 

 the Channel plaice and those of the southern North Sea. 



Maturity brings about a conspicuous migration differing 

 totally from that of the immature. Many of the Northumber- 

 land plaice join the spawning assemblage off the Forth, but some 

 migrate as far contranatantly as the Moray Firth. Fulton has 

 shown in his account of the marking experiments on the coast 

 of Scotland that the Moray Firth plaice may migrate to the 

 Atlantic. It is evident therefore that if originally the products 

 of the spawning grounds are liable to be carried beyond the limits 

 of the school the migrations of the mature are not necessarily 

 confined to the school. 



