ig 



LATER STAGES: PLKIRONKCTIDS 



We arc now in a position to estimate with some degree of exactness the extent of 

 the error in the general statistics due to a variation in length of voyage. As an example 

 the figures for the catch per diem for soles in 190(3—7 are given here with corrected 

 ligures below them. 



B. Ichthyometric. 



lchthyometric work upon market material of soles has been done in Holland in the 

 years 1905—1909, covering about 3500 individuals — 2296 at Ijmuiden and the remain- 

 der at Helder. 



In this country the soles are sold by numbers and in three trade-categories, of "large" 

 "medium" and small. 



The category "large" (Ijmuiden) was found to vary from 30 to 50 cm. 

 „ "medium" (both parts) „ „ „ „ 25 to 40 — 



"small" „ „ „ „ 20 to 36 — 



The fish at Helder are on an average smaller than those at Ijmuiden, the smallest 

 category at the latter corresponding, on the whole, with the "medium" at the former. The 

 category "small" at Ijmuiden has about 5% under 26 cms. in length whereas the same 

 category at Helder has more than 50% under this length. These and other differences 

 are apparently due to the fact that the Ijmuiden trawlers are steam-vessels whereas those 

 at Helder are sailing vessels working nearer inshore and with a smaller mesh. 



It is demonstrated that the value of "small" soles in Dutch ports is greater weight 

 for weight, than that of either "large" or "medium". The fishermen therefore have a 

 great incentive to the capture of small immature soles, and the imposition of a size limit 

 would entail an immediate sacrifice on their part which is not so much in evidence in the 

 case of the plaice. At present "small" soles constitute about 40% of the catch, so 

 far as Holland is concerned. The Dutch experiments form a basis for a determination 

 of standards for different trade-categories of this species, as follows: — 

 A "Large" sole weighs, on an average, -5 kg. 



"Medium" „ „ „ -3 „ (Ijmuiden) 



"Small" „ „ „ -25 „ (other Dutch ports) 



"Small" „ „ „ -l „ 



These figures and conclusions are alone sufficient to show that the problem of ade- 

 quate protection for soles although in its nature of the same kind as that of the plaice, 

 differs from it in several important practical and even biological respects. A further in- 

 stance of this may be evoked by reference to the fact that the sole is a comparatively 

 elongated fish and has various tortuous methods of overcoming the difficulties of trawl- 



