54 



Thirty-ninth Annual Report 



North Sea Current Investigations. 



The effects of sea currents on the conditions which influence the 

 development and growth of fishes and their migration and dis- 

 tribution are of much interest and importance, and have for many 

 years been the subject of investigation by the Board. 



In continuation of the former investigations and in accordance 

 with the scheme prepared by the International Council a large 

 number of drift-bottles were put away during the year, chiefly at 

 five stations, viz., at the Bell Eock ; at Smith Bank, in the Moray 

 Firth ; off Buchannesa ; at Fair Isle ; and at Balta Island at the 

 north of the Shetlands. At the Bell Eock the liberation of the 

 bottles was, through the courtesy of the Northern Lighthouse Board, 

 carried out by the Lighthouse keeper. 



The bottles consisted of ordinary soda-water bottles, and were of 

 two types, viz., one so poised as to float at the surface of the sea to 

 show the surface currents, and . the other weighted so as to drift 

 along the bottom to determine the bottom currents. The bottles of 

 the latter type were provided with a wire " tail," about two feet in 

 length, to keep them off the bottom. Each bottle contained a 

 printed post-card, with directions, in five languages, to the finder to 

 insert the place and date of recovery, and to post the card to the 

 Board's Scientific Superintendent, Aberdeen. 



During the year 2400 bottles were liberated, comprising 1100 

 surface and 1300 bottom drifters. The number recovered up to 31st 

 December 1920 was 140 surface and 150 bottom drifters. This 

 investigation is still in the initial stage, but it may be mentioned 

 that by far the greater number of the surface drifters recovered 

 drifted northwards, many of them having been found off the coast of 

 Norway. In previous experiments the direction taken by the drift- 

 bottles was to the south along the Scottish and English coasts. The 

 reversal of the movement in the autumn and winter of 1920 was 

 probably due to the marked prevalence of southerly winds. 



The Hatching of Plaice. 



Although the stock of adult plaice in the spawning-pond at the 

 Hatchery, Bay of Nigg, Aberdeen, has not been renewed or added to 

 since the year 1913, about one hundred of the fish still remain. Some 

 of these are of small size, and have been bred in the pond. The 

 adults spawned as usual in the early months of the year. It is 

 estimated that fully 2,000,000 fertilised eggs were taken from the 

 pond, rather more, it would appear, than in the previous year, 

 between the beginning of February and the middle of April. 

 Over 1,500,000 of the plaice fry which were obtained were liberated 

 in the sea in the neighbourhood of Aberdeen. 



Since the hatching of the plaice was begun at Aberdeen the 

 number of eggs which has been dealt with is about 450,000,000, and 

 over 350,000,000 fry have been placed in the sea. To what extent 

 this liberation of fry affects the stock is uncertain. The work is 

 carried on in conjunction with the other work of the Marine 

 Station, and involves practically no special expenditure. 



