APPENDIX H: GAESTANü 



24 — 



portionately to the cube of the length, so that in mixed hauls of fishes on the offshore grounds 

 where the average size represents the mean between the sizes of fish of very different weight, 

 the average weight deviates increasingly from the individual curve. 



Increased data wil render the curve shown in the present diagram more smooth and 

 reliable. As an example of the use to which this curve of average weight may be put, I 

 may refer to the question previously raised as to the possibility of drawing an approximate 

 estimate concerning the population of any given area. 



The statistics recently published by Dr. Eedeke^ concerning the catches of Dutch steam 

 trawlers during the last year, include figures showing the weight of plaice per hour captured 

 by tlie commercial fishermen on the different fishing grounds in the different months of the 

 year (Table IX). Converting Dr. Eedeke's monthly averages to the quarterly averages adopted 



Table IX, showing the average weight of Plaice caught per hour on the Dogger Bank by Dutch 

 steam trawlers, the average size on ground 53, the average weight per fish, and the resultant average 

 number of Plaice per hour, together with the average number per hour based on 

 the trawling experiments, for each quarter of the year 



in the present report, we find that on the Dogger Banli tlie commercial catch of plaice per 

 hour in the four quarters of the year was 1,5 kilos., 3.6 kilos., 9.0 kilos., and 4.4 kilos, 

 respectively. Taking tlie average size of plaice on the south part of tlie Dogger Bank 

 Table VIII, ground 53) as representative, we find the average size to be 35.0 cm., 35.5 cm., 

 42.0 cm., and 36,0 cm. in the same quarters respectively. The average weight of fish corre- 

 sponding to catches of these different average sizes may be found from the curve just described 

 to be 510, 560, 1,000 and 600 gr. respectively. Dividing now the weight of plaice per hour, 

 as shown by the Dutch statistics, by the corresponding average weights per fish, we can con- 

 vert the catch per hour of fish from the weight units of the Dutch statistics into their ap- 

 proximate equivalents in numbers caught for each quarter in succession. These numbers are 

 3, 6, 9. and 7 successively. Tbe figures resulting from the scientific investigations are 9, 8, 

 17 and 27 respectively. In each case the average catch per liour of the scientific steamers 

 was apparently greater than that of the commercial trawlers, a result which is probably due 

 to the fact that the Dogger Bank in the Dutch statistics included the entire area covered bj'' 

 grounds 46 and 52 as well as that numbered 53 on the present charts. The abundance of 

 plaice on the northern part of the Dogger Bank can be seen on inspection to be distinctlj' 



North Sea, the probable result of which is a greater loss of weight during the winter in tliis area than 

 elsewhere. This, combined with the slower rate of growth in summer, caused by over-population, may very 

 probably explain the marked defleiencies in the average weight of fishes from this area, as shown by 

 Archer's investigations. 



' Vangstatistieken van Hollandsche ytoomtrawlers, 1903-4. Medodeeliugen over Visscherij, XI, 1904. 



