of the Fishery Board for Scotland. 



257 



below, was much under the supply in former years. Under present 

 circumstances it is not possible to get supplies of living adult plaice 

 from the ordinary commercial trawlers working in the North Sea. As 

 a rule the quantity of plaice obtained by them from near- grounds in 

 any single voyage is small, and it would require many expeditions to 

 obtain a sufficient number for the hatchery ; and the fish would, more- 

 over, have to be purchased at their market value, and the cost of this 

 can scarcely be borne by the present vote for scientific investigations. 

 It is only within the sandy bays near the shore that large quantities of 

 plaice can be secured. 



The eggs were first observed in the spawning pond last year at the 

 beginning of February, which is later than usual, owing to the smaller 

 number of adult fishes in the pond. The spawning gradually increased 

 towards the end of the month, and, as usual, was greatest in March and 

 in the early part of April, declining towards the end of the latter 

 month, and ceasing in the early part of May, a few eggs being obtained 

 on the 13th. The number of eggs obtained in each of the months was 

 estimated to be February, 796,000 ; March, 3,320,000 ; April, 

 3,290,000 ; May, 80,000, making a total of 7,486,000. In the previous 

 year the estimated number was 40,110,000, so that the decrease, for the 

 reason mentioned, has been considerable. 



The estimated number of fry which were hatched out and put into 

 the sea was 4,406,000, the death-rate being thus equivalent to about 41 

 per cent., which is unusually high. The principal cause of this was the 

 impurity of the water and a scarcely adequate supply, especially towards 

 the end of March and the early part of April. Owing to the stormy 

 weather there was sometimes difficulty in filtering the water properly ; 

 and it was found that the arrangement of the filtering apparatus in the 

 re-built hatchery was defective, and the " head " of water was insufficient 

 to furnish a plentiful supply. The fry were put into the sea off 

 Girdleness and Aberdeen on five occasions — in March, April, and May, 

 the last lot being set free on the 23rd of the latter month. 



The temperature of the water varied from 1*5 C. (34*7 F.) to 10-7 0. 

 (51-3 F.) during the hatching season. It was lowest in the early part 

 of March. The specific gravity was under 27 on only six occasions; 

 it was usually about 27*5-27-8, and the lowest was 26'6. 



The number of the eggs of the plaice collected from the spawning 

 pond and the number of fry hatched out are as follows in the different 

 years at Bay of Nigg : — 





Eggs Collected. 



Fry Hatched. 



1900, 



43,290,000 



31,305,000 



1901, 



63,370,000 



51,800,000 



1902, 



72,410,000 



55,700,000 



1903, 



65,940,000 



53,600,000 



1904, 



39,600,000 



34,780,000 



1905, 



40,110,000 



15,790,000 



1906, 



7,486,000 



4,406,000 





332,206,000 



247,381,000 



It may be mentioned that the expense in connection with the 

 hatching work is comparatively small, since it is carried on in con- 

 junction with the Marine Laboratory, and without any additional staff. 

 The total expenditure for extra coals, food for the fishes, etc., is 

 estimated at under £80. 



During the season the hatchery was visited by delegations of fisher- 

 men from the counties of Argyll, Bute, Caithness, and Elgin, under 

 arrangements made with the various County Councils. 



