of the Fishery Board for Scotland, 



401 



2. OBSERVATIONS ON THE EAST COAST, 1891. 



Bell Rock Lighthouse. , 



This station is the only one at any distance from the land. Its 

 situation well out in the North Sea makes it of especial importance, as the 

 observations taken at it necessarily give a more accurate indication of 

 the physical conditions on the western side of that sea than those made 

 nearer land. By these observations an estimate can be made of the 

 physical conditions of the water in which the farther sailing fishermen 

 catch their fish. 



The observations for 1891 have been fairly regular, the readings of the 

 instruments having been occasionally interrupted owing to stormy weather. 

 There are fewer afternoon than forenoon observations. 



The hottest days of 1891 were the first three weeks of August, the 

 mean afternoon temperature being 16° "5 C. No record of air temperature 

 was given before May, so the coldest period recorded was naturally 

 December, with a 9 a.m. mean temperature of 5 o, 0 C, and an afternoon 

 mean temperature of 6°*7 C. 



The surface temperatures showed the same curve as the air tempera- 

 tures, but the maximum (12° '5) occurred a little later in the year, during 

 August (afternoon) and September (forenoon and afternoon) ; while the 

 water was coldest in March (4° "8 forenoon, 4° '9 afternoon) — a range of 

 7°'7 C. for forenoon and of 7°'6 C. for afternoon. 



During the first three months of 1891 the temperature of the surface 

 water remained fairly steady — from 5°*5 at the beginning of the year to 

 4° '5 in March — a regular rise then occurred until July, and the variation 

 was very slight, from 11°'5 to 12° 5, for three months ; thereafter a steady 

 fall happened until the end of the year. (PI. XVIII. %. 1.) 



The extreme range of temperature of surface water was from a minimum 

 of 4°-6 at 9 a.m. on January 21, 23, March 10, 23, 24, 26, and 30, to a 

 maximum of 13°'8 on the afternoon of July 27 — a range of 9 0, 2. 



The mean annual temperature of this water for 1891 was 8°*6 in the 

 morning, and 8°*7 for the afternoon, abaut half a degree lower than that 

 of 1890. 



The mean specific gravity of the water for 1891 was 1026"0 (or 3*37 per 

 cent, of total salts), the same as for the previous fifteen months. The mean 

 monthly density was greatest in August (1026 -3), and least in December 

 (1025-4). (PL XVIII. tig. 3.) The highest specific gravity was regis- 

 tered on August 5 at 9 a.m., and was 1026 - 7 ; the lowest was registered 

 on December 24 at 10 a.m., and was 1024*2. There is little daily 

 variation in salinity, the tides apparently not alfecting the proportion of 

 salts, and the river water evidently not reaching the Bell Rock. The 

 temperature also is practically the same morning and afternoon. 



The smallness of the range of variations of temperature and the con- 

 stancy of the proportion of salts in the waters around the Bell Rock are 

 of special importance, and should have an influence on the distribution and 

 movements of fish, possibly giving rise to less annual change in the amount 

 of the catch in that neighbourhood than nearer land. 



Abertay Light-Vessel 



This station, almost due west from the Bell Rock, is at the mouth of 

 the Tay, and consequently the temperature and the saltness of the water 

 are greatly modified by the neighbouring land and the variations of water 

 in the estuary. The observations from this station were discussed in 



