_ 5 — LATKK STAGIvS: I'F.Kl IRONECTIDS 



Report the data are used fur determination of the occurrence and distribution of the two 

 comnnon and important species of Pieuronectïdae, the plaice and the sole. With regard 

 to the plaice, the conclusion is obtained that there has been a marked and steady "de- 

 cline in the average amoLint of tish taken during the period". The nature of this decline 

 and the evidence of its presence can he observed from the accompanying table (p. 6), the 

 last column of which is extracted from the report. The cause of this decline and how 

 far it represents a real reduction in the. natural supply of plaice on the grounds is not 

 at present clear. 



In the case of soles, there is no such clear evidence of a continuous decline 

 though the figures for 1903 are higher than those for any succeeding year. For this 

 species, the figures represent numbers of fish and not weights, so that a possible de- 

 cline in total weight might be masked by a decrease in average size. But of this there is no 

 evidence. 



As regards distribution, a few general conclusions are drawn. 



"Plaice are very scarce on the shallow grounds off the English coasts — they in- 

 crease as we move eastwards, and they are most numerous on the grounds nearest the 

 continental coasts, the quantities caught decreasing as we proceed northwards and away 

 from the coast". Soles are found in greatest abundance on the English side and increase 

 in numbers from East to West. These conclusions on the distribution of plaice and soles 

 are in agreement with those which can be derived from the general statistics (as shewn 

 in last year's report) and the fact that these special statistics do not provide a more de- 

 finite quantitative expression of the phenomena is due to the small scale upon which they 

 have been collected. 



By combining the sub-areas into three groups, northern, interniediate and southern, 

 it is possible to obtain evidence of periodic or seasonal changes in abundance of plaice. 

 The northern zone showing a maximum catch in summer, the southern zone in winter 

 and the intermediate zone with two maxima, in spring and autumn respectively.. It is 

 possible these facts may be due to periodic migrations from one part to the other, but 

 more evidence is required. 



Certain data were also obtained upon the occurrence of spawning plaice and soles, 

 but these are incomplete. So far as they go they confirm previous work upon the same 

 subject but by other methods. Importance may be attached to this Report not so much 

 because of its definite conclusions but because it illustrates the possibilities of such spe- 

 cial records as an economical and. reliable method, when used on a larger scale, for deter- 

 mining leading facts in the occurrence and distribution of economically important fish. 

 The areas in which the smallest category is most prevalent may be taken as the nur- 

 sery of the species ; those in which aggregations of the largest category take place are 

 indicated by the spawning areas; and seasonal changes in density in contiguous areas 

 or sub-areas are a prime indication of migratory movements. The first requires to be 

 confirmed by special steamer work on the sizes below the minimum size of capture 

 by the trawl, the second requires steamer experiments upon the distribution of the 

 eggs and larvae, and the third requires fish-marking experiments to determine the dyna- 

 mic features or actual movements of the fish. The indications in this Report point to 

 a southern spawning area for the plaice of the Flemish Bight not unlike that shown by 

 the Dutch and German observers by research on the eggs and larvae (see later). This 



