CONSIDERATION OF INDIVIDUAL FISH 57 



attained, but there is no positive evidence of it. The spawning 

 period of the plaice has been very well determined for various 

 parts of the North Sea.'^ On the east coast of Scotland it extends 

 from the end of December in some years, but more usually from the 

 early part or middle of January, to the early part or middle of May, 

 the chief spawning taking place in March. The commencement 

 and duration of the spawning season vary in Northern European 

 waters. In the Danish seas it begins in November, attains a maxi- 

 mum in January and February, and ends in April. 



According to Buchanan-WoUaston^ there are three separate 

 spawning areas for plaice in the southern North Sea ; off Flam- 

 borough, east of the " Dogger " and the Flemish Bight. Of these 

 the last is much the most important, being supplied with fish from 

 distant portions of the North Sea, as proved by the marking experi- 

 ments. The centre of the Flemish Bight area lies to the eastward 

 of the Gabbard and Galloper Lightships. The area seems a well- 

 defined one, the greatest number of pelagic eggs being found near 

 the centres of highest salinity and temperature. 



In Loch Fyne in the Firth of Clyde no plaice eggs were found in 

 1898 until the middle of February, and there were none left after 

 June. In the Irish Sea the writer has taken the eggs of the plaice 

 in mid December in Cardigan Bay, but the main spawning season 

 is in March. From a quarter to a half a jnillion eggs are produced 

 by a female plaice, this being a considerably smaller number than 

 that of some of its near relatives. The turbot produces on an 

 average over 8| millions, the flounder about a million, and the sole 

 about 570,000 eggs. The eggs are naturally not extruded at once, 

 the process of spawning being a gradual one. This is a physical 

 necessity, since the female cannot hold all the eggs at the size they 

 attain when mature, and they must ripen gradually and in succession. 



It is evident that during the spawning season an immense number 

 of fish eggs must be present in the seas round the spawning grounds, 

 and efforts have been made to determine the numbers approxi- 

 mately. Reference is made below to the estimates made by Hensen^ 

 in the Baltic to determine the number of cod and plaice eggs in a 

 certain area (p. 234). In a similar manner, Williamson* determined 

 the number of plaice eggs in Loch Fyne in the spawning season of 

 1898 to be 483 millions. 



• Wemyss Fulton, " On the Spawning and Fecundity of the Plaice," 24^/1 Ann. 

 Kept. Scots. Fish. Bd., Part III, 1906. 



^ H. J. Buchanan- WoUaston, Report on the Spawning-grounds of the Plaice in the 

 North Sea. Board of Agriculture and Fisheries. Fishery Investigations. Series II. 

 Sea Fisheries, Vol. II, No. 4. London, 1915. - 



' Hensen und Apstein, Wiss. Meeresuntersuch. Kiel Commission. Bd. 2, N.F. 

 Heft 2, p. 71, 1897. 



* lyth Ann. Rept. Scots. Fish. Bd., p. 79, 1898. 



