CHAPTER VI 



LIFE-HISTOEY OF THE PLAICE 



The discussion of the plaice problem has been immensely 

 obscured by a tendency to confuse two totally different things — 

 symptoms and remedies. 



It is proposed here to try to keep the two quite distinct. 



Spmvning 



Plaice in the North Sea are believed to spawn chiefly in water 

 between 20 and 30 fathoms in depth. Spawning areas have 

 been located at those depths (in areas which marine biologists 

 classify as ' C ' areas) off the Firth of Forth, the Moray Firth, 

 outside Flamborough Head, in the middle of the Flemish 

 Bight, and in the ' Clay Deeps ' between the Dogger and the 

 eastern shore of the North Sea. 



Spawning takes place chiefly in January, February, and March.^ 

 The eggs measure about one-twelfth inch in diameter ; ^ they 

 float at the surface so long as they remain in sea water of normal 

 buoyancy. They hatch out in a period said to vary from 

 a fortnight to a month, according as the temperature is com- 

 paratively high or low (about 50° F. to about 41° F.). During 

 this period the eggs naturally drift ' downstream ' of any 

 current in which they find themselves. From the eggs emerge 

 the larvae — about two-sevenths of an inch long. 



TJie Larval Period 

 To each of these larval fish is attached a ' yolk-sac ', which 

 contains a supply of food. The little creatures live, at first 

 entirely, and afterwards partially, on the contents of this 

 yolk-sac until it is absorbed. All this time they are perfectly 

 helpless ; they can make spasmodic and uncontrolled move- 

 ments, but have little controlled ' poise ' in the water, and 

 apparently no sense of direction. It follows that they, like 

 the eggs, will move downstream. They have no power to avoid 

 a predaceous attack, and are more likely than the eggs to be 

 destroyed by enemies, for in the sea, as ashore, immobihty 

 is the best form of protection, and the larvae, by their 



^ The extreme limits are December to May. Jovrn. M.B.A., vol. xii, No. 2, 

 p. 194. 



- I. e. about 200,000 eggs to the fluid quart. 



