PART I 



SUMMARY AND DISCUSSION OF RESULTS 



General Statistics 



In the first Report on Pleuronectidae (1909) the English fishery statistics were 

 taken as a basis for determination of certain points in the topographical and bathymétrie 

 distribution of each of the more important species of Pletironectidae. 



The potentialities and limitations of general statistics for such a purpose were 

 discussed. Two series of ratios were employed, namely, percentage proportion by weight 

 of each species to the total catch (or K) and the catch of each species per day's fishing 

 (or Ki). It was shewn that each of these ratios has considerable sources of error but 

 that for broad general deductions, covering large areas, they may be employed advantage- 

 ously for general indications of distribution, especially when compared with each other. 



During the period now under review the English report for 1908 has appeared and 

 the data thus made available have rendered it possible to attempt an investigation into 

 the seasonal distribution of the more abundant Pleuronectidae of the North Sea. To 

 this end the catch per diem (K 2 ) for each area of the North Sea has been taken and has 

 been divided up into monthly periods. The scope of the figures has in this way not 

 only been reduced to t \- L jûa., but owing to inequalities of fishing, has in some months 

 suffered a still further reduction. To minimise the effect of this and to eliminate annual 

 fluctuations, the figures for the four years (1906—9) have been combined, by taking the 

 mean average for each month. Even then, the monthly series are by no means com- 

 plete and it has been necessary to omit for the present the consideration of certain of 

 the more rarely occurring species, such as flounder and halibut. The best results are 

 obtained from the plaice, dab, sole, and turbot, which are indigenous shallow water types, 

 though indications of seasonal changes are obtained for the deep-water species, the witch 

 and megrim. 



In the First Report, the sources of error in the figures of catch per diem (or per 

 day's absence from port) as a basis for showing quantitative distribution were indicated. 

 The principal of these is the variation in distance of each area from the various ports of 

 landing, resulting in a different length of voyage and probably a different number of 

 hours' fishing per days' absence from port. In studying the monthly changes in catch 

 per diem for each area separately this error is greatly reduced shough it cannot be said 

 to be altogether absent. 



