APPENDIX H: GARSTANG _ 22 — 



abundance dui-ing the July to September quarter. Taking again as an example the series of 

 grounds from Horn Reef to the Dogger Bank, and proceeding from east to west, the catch 

 per hour of the small plaice during the J^t quarter on the four grounds numbered 30 to 33 

 inclusive is 75, 2, 1, and 0'6 respectively. Even the frequency of. the larger plaice is rela- 

 tively insignificant, being 18, 3, 2, and 2 on the same four grounds in succession. These 

 figures contrast markedly with the abundance of the small plaice on the same grounds during 

 the summer quarter, when the catch per hour of the plaice below 30 cm. is 906, 664, 63 

 and 32 on the same four grounds. Other instances of the same character are to be found 

 in the charts, and the explanation clearly resides in the offshore migrations of the small plaice 

 during the summer months, as previously displayed in the description of the experiments upon 

 marked plaice. 



Another point which is clearly revealed by the figures upon the charts is the far greater 

 abundance of small plaice, even in the same depth of water, in the eastern than in the western 

 parts of the North Sea. If the areas numbered 55, 56, 67, 68 and 69 be taken into con- 

 sideration it will be noticed tliat not only is the percentage of tlie smallest plaice higher off 

 the Dutch coast than off the English coast, but the actual abundance of the plaice below 30 

 cm. is still more strikingly in excess on the eastern than on the western grounds under con- 

 sideration. These results are also in entire agreement with the results of the marking experi- 

 ments previously described, from which it was apparent that the plaice on the Leman Ground 

 and Leman Shoals (nos. 68 and 69 on the charts) were largely derived by emigration from 

 the Dutch nursery grounds. 



The figures in fact, so far as they are based on a sufficient number of hauls, are so 

 consistent with one another and with the experimental data previously discussed, that there 

 can be little doubt as to the great progress already made towards a correct representation of 

 the conditions which prevail upon the more important North Sea trawling grounds. These 

 results are limited to the data yielded by the scientific experiments during the year 

 and a half prior to June, 1904. It may be reasonably expected that the gaps which 

 exist on a certain number of the grounds will be filled up in the further course of the 

 investigations. 



In order to facilitate a comparison between the average figures sliown in the charts and 

 the separate figures resulting from individual hauls of the trawl, two groups of sections have 

 been provided upon which the characters selected have been separately displayed for each haul 

 of the trawl and for each of the four quarters of the year. Tlie sections follow two lines : 

 (1) From the north part of the Dogger to the Horn Eeef Grounds (Eig. 2 — 5, p. 20) and (2) 

 Prom the English coast north of the Wash to the Dutch coast south of Helder (Eig. 6 — 9, 

 p. 21). These sections have the advantage of showing more graplücally the relation which exists 

 between the average size as well as the abundance of small plaice and depth and distance 

 from shore. 



In any future edition of charts concerning the trawling investigations it would be 

 exceedingly instructive to add also figures showing the average weight of fish per hour 

 and the average weight per fish in each of the areas finally adopted. As, however, the 

 material on this point, at present placed at my disposal, is limited to the weight determined 

 during the Dutch and English experiments, it has not appeared profitable to place these figures 



