_ 25 — APPENDIX H: GARSTANG 



less than on the south part of the Dogger Bank. It is interesting-, however, to observe that 

 botli methods of enquiry lead to the conclusion that the abundance of plaice on the Dogger 

 Bank is greater in the six last months of the year than in the first six. 



An otter trawl of 90 foot headline is usually considered to have a spread of about 60 feet ^ 

 and thus covers about 1/40*^^» of a square sea-mile or about l/12th of a square kilometre per hour, 

 assuming the rate of towing to be 2'/2 sea-miles per hour. Taking the average catch of 

 plaice per hour on the Shoal of the Dogger at about 15 fish and the area of the south part 

 of the Dogger at about eight thousand square kilometres, it thus appears that the whole of 



this area, if once trawled over, would yield ^, = 1,440,000 fish. We do not at 



present know either the total quantity of fish which is landed from the Dogger Bank for any 

 portion of the year, or the total number of voyages which are made by fishing boats to the 

 same region ; but if we assume that three or four millions of plaice represent the maximum 

 total catch of plaice on the south part of the Dogger Bank, in the course of a year, we shall 

 obtain a figure which, though exceedingly rough, will probably serve for our present purpose. 

 The intensity of fishing on the Dogger Bank as shown by the Dutch marking experiments 

 (See table 2) was 13.9 per cent, per annum, say 14 per cent, or V?*'' of the total population. 

 Taking '/s''' as probably more closely approximating to the real intensity we may conclude that 

 the total population of plaice on the south part ot the Dogger Bank is not more than 15 or 

 20 millions. The annual addition of 5 or 10 million plaice by transplantation to the Dogger 

 Bank would thus appreciably increase the catches of the fishermen on tliat ground, and would 

 enable the transplanted fish to attain marketable size and weight far sooner than on the in 

 shore grounds where their growth is arrested by the great density of the population. 



E. The protection of undersized fish 



Though not expressly stated in the preceding sections of this report, it must be apparent 

 that the investigations in progress have been devised very largely in order to throw light 

 on the various biological factors necessary for the scientific treatment of the "undersized fish 

 question". Before it is possible to recommend a special size-limit, or even to admit the pro- 

 tective value of size-limits at all in the case of trawlers, it is necessary that we should be 

 sufficiently informed upon the following points concerning the life-histoi'y of the plaice: 



(1) the localities where small plaice are particularly abundant; 



(2) the extent and position of the offshore areas supplied from these "nursery" grounds: 



(3) the size, age and seasons at wliich the small fish migrate from the inshore grounds; 



(4) the rate of growth on the inshore grounds; 



(5) the rate of growth on the various offshore grounds. 



' cf. Fulton, XX th Annual Report Sbottish Fishery Board, p. 118 et seq 



Appondix il 4 



