— 25 — 



million plaice from 15 to 76 cm. in length and from 37 to 4477 g. in weight. The 

 average length of all plaice landed is about 29 cm., the average weight calculated 

 empirically (from weighings of partly cleaned, partly entire fish) 258 g., calculated 

 theoretically {k = I) 271 g. ; the former is 0.952 of the latter. 



The interval with the highest number of specimens (mode or D) is 25 cm. The 

 part of the series below this length (ascending arm of the curve) is subject to a market- 

 selection; that is, of the small plaice actually caught up to a length of 24 cm. not the 

 whole catch but only a portion is landed; on the other hand — apart from chance loss 

 — all the plaice caught above 25 cm. in length are brought to market. The plaice 

 only partly landed up to and including those at 24 cm. in length, which we may con- 

 veniently call "undersized" plaice, have an average age of 2, 3 to 3V3 years. The 

 quantities of these brought to market compose about Vsrd (32 Vo) of the number and 

 about V7th (14 "/o) of the weight of the total landings. The percentage of undersized 

 plaice discarded by the market-selection increases, the smaller the plaice are and in a 

 very rapid manner. Thus, the plaice below 23 cm. (up to and including 22 cm.) 

 compose only 14 "/o by number, only 5 ''/o by weight of the landings, those below 20 

 cm. (up to and including 19 cm.) only i "/o and 0.2%; those below 18 cm. only o.oi Vo 

 by number and 0.0015% by weight of all landings. 18 cm. is the size-limit used 

 consciously in practice, though not imposed by law, and we can see how the first-class 

 vessels keep well above it. Of the 112.5 million plaice landed only 11,250 approxi- 

 mately are below this size-limit. The plaice below 29 cm. in length have been called 

 here generally "small" plaice; this has been done, after examination had shown, that 

 the quantity of these plaice by number and weight in our measurement series (about 

 63% and 40^/0) agree well with the corresponding quantities in the landings; though 

 the market-class "small" admittedly contains a number of plaice which are larger than 



28 cm., yet their number is fairly well counterbalanced by the number of plaice below 



29 cm., which are included in the market-class "medium". In the same way, we may 

 call the plaice over 35 cm. "large", the plaice between 29 and 35 cm. in length thus 

 forming the group "medium". The proportions of these three groups small, medium 

 and large are, by number, 63 : 27 : lO; by weight 37 : 32 : 31; or, again, by number 

 7 : 3 : I ; by weight almost 1:1:1. The "small" plaice are on an average 2 to 4 

 years old, the "medium" 4 to 5 years, the "large" 5 to 25 and more years. Among 

 the small plaice almost all the males, but very few females are mature; among the 

 medium all the males and about Vsrd of the females, among the large almost all the 

 females also. 



The length above and below which 50 Vo of the number of all plaice in the Eng- 

 lish landings lie, i. e. the central or median value of the number series, is 27 cm. The 

 two lengths, between which half the number of all plaice lie, i. e. the two quartiles, are 

 24 and 31 cm. This interval is thus the predominant range of the series; it contains 

 plaice at an average age of 3V2 to 4 years; 10% of these are undersized, 40 "/o small 

 and loVo medium plaice. 



The length, above and below which 50% of all the plaice by weight lie, i. e. tJie 

 median or central value of the weight series, is 3 1 cm. ; the corresponding quartiles about 

 26.5 and 38.5 cm.; between these lie 50 Vo of all plaice by weight; they form the 

 predominant range of the weight series, including abt. i 5 "/o of small, 30 "/o of medium 

 and 5 Vo of large. 4 



