INTERNATIONAL FISHERY INVESTIGATIONS. 387 



experiments on the Dogger Bank in the spring of 1904 resulted in the 

 recapture of more than 40 per cent of the Plaice exceeding 25 centi- 

 metres (10 inches) in less than twelve mouths. From this result it 

 seems clear that the total annual catch of the fishermen no longer forms 

 an insignificant proportion of the total stock of Plaice. 



Trawling experiments in the area under investigation with an otter- 

 aud a beam-trawl of the ordinary commercial patterns have given 

 extensive information as to the distribution of fishes of different sizes, 

 and the results obtained, when combined with those of the marking 

 experiments, have done much towards furnishing a preliminary view of 

 the natural history of the fishes in the southern half of the North Sea, 

 and of the Plaice in particular, its distribution at different sizes, and 

 the seasonal movements which it undertakes. 



A Series of experiments on the transplantation of small Plaice from 

 the inshore nurseries to the open waters of the Dogger Bank in the 

 middle of the North Sea, carried out in 1904, has thrown much new 

 light upon the condition of the fishing grounds. The increase of weight 

 of small plaice marked and transplanted in early spring from the 

 crowded inshore grounds to the Dogger Bank was found in the following 

 winter to be six times the normal increase of marked fishes of the same 

 size left on the inshore grounds. Such a result suggests that the central 

 grounds of the North Sea possess a larger food supply suitable for the 

 nourishment of the Plaice than is at present made use of, and that they 

 may therefore be capable of maintaining a much larger population 

 of Plaice than now exists upon them, whilst on the nursery grounds 

 owing to undue competition for the food available the Plaice are unable 

 to attain their maximum rate of growth. Whether transplantation on 

 a commercial scale from the small-fish grounds to the Dogger Bank or 

 other suitable localities would be a practical method of increasing the 

 total weight of Plaice available for capture in the North Sea is a 

 problem concerning wliicii further information and experiment will 

 be required. Quite apart from this question, such a result as that 

 already indicated is of the greatest significance for the proper under- 

 standing of the condition of the Plaice fishery and of the methods 

 proposed for improving it by the prevention of the capture of immature 

 fish. 



Particular attention has been paid to the study of the age of fishes 

 of particular sizes and to their rate of growth. It has now been shown 

 that by an examination of the otoliths or car-stones a precise estimate 

 of the age of individual fishes can be arrived at, the ott)liths showing 

 alternate white and dark rings, the white rings formed in spring and 

 early summer, the dark in late summer and autumn. This method has 

 been applied in detail to a considerable number of Plaice from fishing 



