4o6 Garstang : The Disappearance of the Plaice. 



North Sea, 1409 have been caught and returned within twelve 

 months. In the years from 1903 to 1906 the recapture of the 

 marked fish was, of the very small, 11 per cent, per annum ; 

 from eight to nine inches, 21 per cent. ; ten to eleven inches^ 

 33 per cent. ; twelve inches, 35 per cent. ; fourteen inches, 

 40 per cent. ; larger fish, 24 per cent, or a percentage of 23 of 

 all sizes. Now if the fishermen caught 40 per cent, of the four- 

 teen-inch marked plaice within a year, it may be fairly estimated 

 that they caught 40 per cent, of the unmarked fourteen-inch 

 plaice. The trawling is evidently so intense that amongst the 

 fish of a marketable size the fishermen are catching from 33 

 to 40 per cent, in one year. If 1000 female plaice were placed 

 in the sea, say of eight or nine inches, and three years old, 20 

 per cent, would be caught in the first year, leaving 800 four 

 year olds. The fishermen would catch 30 per cent of these 

 in the following year, leaving 569 five year olds. At that age 

 the female plaice begin to breed, but only in a very small 

 proportion. One tenth (56) of these might be estimated as 

 breeders. The fishermen caught 40 per cent., leaving 336, of 

 which two-thirds (224) were breeders, and, after that time all 

 would be mature. The result is that from the 1000 fish there 

 would be only 728 breeding operations during the eight years 

 following the onset of maturity, which means that only about 

 three-quarters of the three year old stock would ever breed 

 once at all. In the unfished sea out of a thousand plaice the 

 total breeders, after allowing for depletion by natural enemies 

 such as sharks, would be 4841 in the same number of years 

 by the same table. The net result is more than interesting, 

 and is of vital importance. The fishing in the North Sea under 

 the present conditions gives only one breeder for every six or 

 seven that would have been secured in the unfished primitive 

 times. As a result of the intense fishing, the age of the spawners 

 or the age of breeding is reduced. In the unfished area the 

 average age that most fish start spawning is about eight years ; 

 in the North Sea now it is six years. This means that we are 

 putting a premium upon early breeding, and again this is a 

 matter for consideration whether we are not thereby lowering 

 the stamina of plaice, and encouraging a race of small plaice. 

 In the English Channel, where trawling is an old occupation, 

 they begin to breed at a very early age ; in the south of the 

 North Sea the}' begin breeding a year later, and in the north 

 of the North Sea a j'^ear later still, whilst in the White Sea 



Naturalist^ 



