APPENDIX H: GARSTANG — 12 — 



(near Helgoland) from May, 1903 to May, 1904 mclusive, 97 were taken by sailing trawlers, 

 and only 11 by steam trawlers, i. e., 90 per cent, by the former, and 10 per cent, by the 

 latter class of vessel. The excess of captures by sailing boats would be seen to be still 

 greater if we were to omit from consideration those fishes which were recaptured outside the 

 20-meter contour line. 



A similar result is shown by the English records of marked fish recovered in the southern 

 part of the North Sea, between the coasts of England and Holland. 



In interpreting these figures some allowance must be made for the greater facility with 

 which marked plaice can be detected on small boats than on steam trawlers; but, whatever 

 allowance be made under this head, it is fairly clear that the sailing boats capture at least 

 as many small plaice as do tlie steam trawlers. 



Fuller details concerning the percentage of recoveries for all sizes of the fishes marked 

 are given in the accompanying table (Table III, p. 11). 



5. Rate of growtli 



So much diversity has been revealed by the international experiments in regard to the 

 rate of growth of plaice, not only of different size, but also on different grounds, that the full 

 treatment of this problem must be reserved for the definitive report of the Committee. A large 

 amount of additional information based on a study of otoliths and of frequency curves will then 

 be available in addition to the evidence of the marking experiments. 



In the English and Dutch areas, adjacent grounds show very marked differences in 

 regard to the rate of growth, and, as the fish migrate successively over the whole of this area, 

 the monthly averages of growth which have been calculated from the existing data show con- 

 siderable fluctuations. For plaice between 20 and 30 cm. in length the annual rate of growth 

 appears to be about 7 cm. 



On the eastern grounds of the North Sea the Danish experiments provide abundant 

 material for showing the normal rate of growth for marked fish of this size. The year's 

 growth on the Horn Reef Grounds lies between 4 and 5 cm., without making any allowance 

 for the normal shrinkage of the fish after recapture and death. 



In the Skager Eak the Danish experiments show a higher rate of growth than that on 

 the Horn Reef Grounds, the average growth appearing to be about 7 to 8 cni. in one year. 



B. Transplantation experiments 



In the spring of the present year (1904) the Danish and English investigators, taking 

 advantage of the differences in rate of growth already revealed, carried out special experiments 

 to determine the effect of transplanting a large number of small plaice from the coastal grounds 

 to the offshore waters. 



