38 LIFE-HISTOEY OF THE PLAICE 



These ' nursery grounds ' inside the 10-fathom Hne are known 

 to scientists as the A 1 , A 2, and A 3 areas ; and fishermen call 

 the latter, and grounds immediately west of it, as far as the 

 20-fathom line, the ' Small Plaice Grounds '. Young plaice 

 at the end of their first summer average 3 J inches in length,, 

 and run twelve to the ounce in weight ; a year later they 

 average 5f inches and weigh about one ounce ; and in the third 

 autumn they are SJ inches long and weigh about three ounces. 

 During this period the tendency seems to be to spend the 

 summer inshore, and to move out into deeper and warmer 

 water up to 20 fathoms in the winter ; and as the fish grow 

 they naturally come a little less close inshore each summer. 

 Meanwhile the food is gradually changing from the ' fry food ' — 

 worms and small Crustacea — to the adult food, chiefly cockles 

 and young mussels, which live respectively buried under about 

 half an inch of sand and in more or less brackish water on clean 

 bottoms. 



Maturity 



Generally speaking, male plaice are mature at the end of the 

 fourth summer, and females at the end of the fifth. The size 

 of the fish will by this time vary enormously according as it has 

 frequented grounds w^here food is more or less plentiful, and 

 according as it has lived in deep or shallow w^ater. 



* Eange ' has been shown by Borley to be a most important 

 feature in determining the growth of fish, as it is in the case of 

 mammals ; and the rule ' Big Waters — Big Fish ' seems to be 

 as generally true as the mountain shooter's rule ' Big Hills — 

 Big Heads ', provided always that the deep-sea valleys or the 

 big mountain ranges are not barren of the food of the species — 

 as is the case in the Barents Sea. 



The minimum sizes at Avhich plaice have been found to be 

 mature by Hefford in the southern North Sea in 1910-11 were : 



Males . . .14 centimetres (o| inches) 



Females . . .19 centimetres (7^ inches) 



But most of his ' milters ' were 7-8 inches to 9-4 inches in length, 

 and, while there was a considerable number of mature females 

 between 91 inches and 12 J inches in length, it was apparent 

 that a comparatively small percentage spawned before they 

 reached 10|- inches. 



On the Dutch and German coasts, it is beHeved, most males 

 are four, and most females five years old before they spawn. 

 In the north of the North Sea maturity in each sex is probably 

 a year later. 



A very large female plaice may contain as many as half 



