6 Part III. — Twenty -eighth Annual Report 



In the Firth of Clyde, and in particular in Loch Fyne, the investi- 

 gation into the herring fishery which has been in progress for 

 the last few years was continued, and observations on the tempera- 

 ture of the water and the relative abundance of plankton were made 

 as frequently and regularly as circumstances allowed. This subject 

 is dealt with more fully below. 



Among the researches in progress, but not yet completed, may be 

 mentioned the relation between the salmon fishery and the herring 

 fishery in Loch Fyne, the destruction of immature herrings by sea 

 birds, and the reproduction of fishes. 



The Hatching of Plaice. 



During the season of 1909 the hatching- work was continued at 

 the Bay of Nigg as in previous years. The methods employed have 

 been fully described in some previous Reports, the essential features 

 being the retention of the adult fishes in a large tidal pond, where 

 the eggs are shed and fertilised in a natural way during the spawning- 

 season ; the collection of the floating eggs from the pond and their 

 transference to the hatching apparatus, where also the larval fishes 

 are kept for some time after hatching occurs. 



In the course of the previous autumn considerable numbers of live 

 plaice were obtained by the " Goldseeker " in the Moray Firth and 

 added to the stock already existing in the spawning pond. In con- 

 sequence of the increased supply of spawners, the number of eggs 

 collected in the coarse of the season was larger than in the previous 

 year, amounting to about 19,749,000, as compared with 15,332,000 in 

 1908 — the increase thus being about 4,417,000. The first eggs were 

 collected on 21st January, and collections were made thereafter 

 almost daily till 26th May, when a few thousands were obtained. The 

 spawning in the pond thus extended over eighteen weeks, but, as usual, 

 by far the greater proportion of the eggs were shed in March, and 

 particularly just after the middle of the month. The number of eggs 

 obtained in each month of the season, and the percentages, were as 

 follows : — 



Number of Eggs. Percentage. 

 January, - 87,000 0'44 



February, - - 2,890,000 14-6 



March, - 10,860,000 55'0 



April, - 5,387,000 27'2 



May, .... 525,000 26 



The number of dead eggs which were removed from the hatching 

 apparatus was estimated at 3,134.000, or a little under 16 per cent., 

 which is a lower proportion than usual. The specific gravity of the 

 water during the season varied from 26*2 to 27'4. and the tempera- 

 ture from 2-6° C. to 11 4° C. 



The number of living fry of the plaice obtained from the hatching 

 apparatus in the course of the season was estimated at about 

 16,615,000, as compared with 12,296,000 in the previous year — an 

 increase of 4,31 9,000. They were liberated in the sea in nine lots, 

 between 25th February and 12th June. About half of them were 



