240 



Pari III. — Seventeenth Annual Report 



female plaice appears to be 19-20 inches. These figures, however, are to a 

 certain extent influenced by the amount of fishing, or rather over-fishing, 

 that has taken place at the different places. He found males and 

 females in a ripe condition about seven inches long, and as the minimum 

 size at maturity may be considered a measure in regard to the size of the 

 race it is concluded that the plaice living in these Danish waters belong 

 to a smaller race than the one existing on the Scottish east coast, where Dr. 

 Fulton has found the minimum size of the male at maturity to be 

 about thirteen inches, and of the female about fifteen inches.* 



In a series of Tables Petersen has illustrated the results of a great 

 number of hauls made with several kinds of gear in different localities 

 and at various times of the year, and the several groups of plaice shown 

 in the Tables have been marked by him according to the age he considered 

 them to be. From this classification it will appear that the growth- 

 rate of the plaice in these waters should be considerable. Petersen has, 

 for instance, suggested that the smallest spawning fishes are in their 

 second or in their third year (page 3). But if it is taken as proved that 

 the plaice in the Kattegat belongs to a smaller race, then there is strong 

 reason for believing that the growth-rate per year should also be less than 

 on the Scottish east coast. In that case, however, the groups formed by 

 the fishes captured by Petersen cannot always represent the natural 

 annual series, but must be somewhat artificially produced combinations, 

 and therefore misleading. Petersen himself seems to have had a feeling 

 of this kind in one case (page 17), when he suggests that the different 

 ways in which the investigations were sometimes conducted might have 

 had some influence in this respect. I think that this may be proved in 

 several cases from his Tables. And not only the kind of gear will 

 influence the size of fishes captured, but also the depth of water and the 

 extent of bottom area examined at the various depths. Petersen's ideal 

 mode of illustrating the various annual groups appears to be (page 18) 

 to capture, if possible, an equal number of each of them, thus getting 

 rid of undue influence by the greater range of growth shown by the groups 

 comprising the greatest number of fish. This method would certainly 

 give an excellent result if it was known beforehand where the greater 

 mass of each group was located. 



But as this is not and cannot be known with accuracy until the fishing 

 has been conducted and the results examined, the choice of the fishing- 

 places will mostly be a mere matter of guess. Petersen has generally 

 investigated certain selected depths only, sometimes miles apart, and the 

 grand total of a number of hauls made, nay even each individual haul, 

 cannot claim to be a true representation of distinct annual series ; they 

 may or may not be so ; under normal conditions there is no reason why 

 they ought to be. The correctness of this statement is evident from the 

 following : — 



[Table. 



Tenth Annual Report Fishery Board for Scotland, Part III., p. 239, A. \ 



* " Race " is not here meant to imply distinction between the Plaice in the Kattegat 



and on the East Coast of Scotland further than differences in growth rate, which may be 



due to more or less favourable conditions of growth only. 



