COUNCIL - SEPT. 1912 — APPENDIX M — 144 — 



lies at 24 cm., that is to say this is the length class to which the greatest number 

 of plaice belong. Of this total quantity landed, 20 "/o in weight and 40^0 in num- 

 ber (about 81 million fish) are plaice under 25 cm. in length and less than S^/s 

 years old. Only 6 "/o of the number are over 35 cm. long and over 5 years old, 

 i. e. have passed the average age of maturity of the female plaice. The great 

 mass, the real stocli of the plaice landed , about 54 "/o of the weigth and 60 "/o 

 of the number, consists of plaice from 25 to 35 cm. long and from 3V2 to 5 years 

 old. The limit of possible age for North Sea plaice is 30 years or more. 



The essential part of the plaice landed by the fishery in the North Sea must 

 thus be regarded as "young fish" and only 10 "/o at the outside have produced 

 eggs before being captured^ i. e. have contributed to the maintenance of the stoclf. 



Far greater than the quantity of plaice landed by the fishery, and utihsed 

 in the market for human consumption, is the quantity annually caught, by 

 which the North Sea stock is reduced. Investigation has shown that in summer, 

 on the young fish grounds of the coast, from twice to five timas as many plaice 

 as there are landed, are thrown overboard again, for the most pai't dead, by first 

 class fishing vessels working with the trawl. Besides the 203 million plaice annu- 

 ally landed we have then also an estimated number of about 300 million small 

 fish of 24 cm. down to 10 cm. in length, which are uselessly destroyed, mak- 

 ing an annual total of abt. 500 plaice taken from the stock in the North Sea. 

 These figures are, moreover, without doubt too low, as the catches of the small 

 and very small coast fishing vessels still remain to be added. Of these 500 million 

 fish, three quarters of the number are under 25 cm. long, and only 2 "/o are over 

 35 cm. in length and 5 years of age. 



These figures clearly point to a destructive effect on the plaice stock caused 

 by the trawl fishery, proving, in any case, that an imprudent exploitation of the 

 same takes place. 



How far the annual removal of 500 million plaice must be regarded as really 

 disastrous to the stock in the North Sea depends on the absolute size of this stock. 

 There are several methods of determining this size of the stock. 1) Determi- 

 nation of the quantity of plaice eggs annually spawned in the North Sea, cal- 

 culating therefrom the number of females annually spawning, and finally arriving 

 at the total number of plaice to be found. 2) Calculation of the so-called 

 fishing -co efficient i. e. that percentage of the total stock, annually taken by 

 the fishery, by means of marked plaice. 3) Calculation of the catch- coeffici- 

 ent of the trawl generally employed, i. e. the percentage of the total number of 

 plaice actually present on a certain area of bottom which is taken by the trawl 



