RAPPORTS. XIV: MASTERMAN - 20 — 



nets. The question of mesh regulations for plaice is largely influenced by the presence 

 of soles and by the high value of the young soles, as emphasised by the authors. Young 

 soles of 17 to 18 cms. pass readily through the ordinary otter trawls but the same-sized 

 fish and even smaller are retained by the beam trawl of the sailing vessels. This con- 

 sideration is of even greater import in England than in Holland on account of the large 

 (both absolute and relative) quantities of soles caught by the sailing trawlers of Lowes- 

 toft and Ramsgate. Until ichthyometric data similar to, or more extensive than these 

 Dutch observations are obtained for the English ports the scope of the sole problem will 

 not be evident. 



C. Biological. 

 Age of plaice. 



Another contribution upon the age of Plaice in the North Sea and English Channel 

 has recently been published (2 b). 



The author relies, as in former work, upon the determination of age of otoliths. This 

 method is indeed the only one which is practically available for age determination of 

 plaice on any large scale, and so much has it been employed that its value and its limi- 

 tations are now fairly sharply defined. 



The material employed was almost exclusively provided by the S. S. Huxley and 

 consisted of over 20,000 individuals. They were obtained from the parts of the North 

 Sea lying southward of a line from Flamborough to the Naze, or the A, B and C, 

 statistical areas, and from the English Channel off the Devon coast. 



It is shown that the prédominent age-group varies from I in the Devon Bays to V 

 in certain parts of the Flamborough Off and Eastern Deep Grounds. In the inshore 

 grounds along the East Coast of England, (Lincoln and Norfolk) along the Dutch coast 

 and off the Devon coast (in Great West Bay) the II group predominates. In the offshore 

 grounds contiguous to these, such as the Leman Ground, Brown Bank, Gabbard Deep 

 and Horn Reef Outer, the III group is predominant, whilst in the central parts of the 

 North Sea, including the Dogger Bank, Clay Deep, Flamborough Off and Eastern Deep, 

 the IV and in some cases the V Group predominates. There is a general agreement 

 between these results and those obtained from the returns of commercial trawlers, in so 

 far as the areas investigated are similar. 



Each research of this nature adds to the accumulative evidence for (1) the distribution 

 of the plaice of the North Sea, in belts of each age group extending seawards, (2) the 

 decreasing density of this species as the central grounds are reached and (3) the general 

 inference that the North Sea plaice brought to market are chiefly three to five-year-olds. 

 The earlier hauls of the "Huxley" appear to have been distributed over the southern 

 North Sea without any definite plan or scheme of distribution. A consideration of the 

 distribution of plaice seawards, according to age, but more intimately according to size, 

 shows that the earlier attempts to determine the average growth of plaice on a given 

 ground must necessarily be fallacious when based upon the comparison of the average 

 size of different age-groups, unless the area investigated is sufficiently extensive to include 

 the whole extent of the age-belt investigated. In recognition of this fact the "Huxley" 

 made, in September 1905 and again in May IQ06, a series of hauls along a line running 

 N. W. from the Texel in a direction intersecting the known belts of II, III, IV and V 



