Distribution of Plaice and Plaice Eyys. 51 



No doubt the time of .spawning is influenced by the temperature, 

 as it has been observed that in the Moray Firth area spawning occurs 

 later and later in an easterly direction. 



A study of the distribution of the main spawning areas in the 

 Northern North Sea and the influence of the prevailing currents on the 

 passive eggs and helpless larvae suggests that there is probably little 

 or no interchange between the stock of plaice on the Scottish Coast 

 and that of the Southern North Sea. Even in statistical areas XXIX. 

 and XXX., where the depths are not excessive, small plaice are but 

 poorly represented since the south-westerly branch of the main 

 current tends to carry coastwise eggs spawned within or to the north 

 of these areas. 



The selection of such definite spawning places ; the influence of 

 the prevailing currents on the plankton stages ; the gradual off- 

 shore movement of the young plaice with increasing age and size ; 

 the compensatory northerly movement of adult plaice ; all tend to 

 show that the stock of plaice on the Scottish coast is practically 

 a self-contained one. The life-cycle from egg to adult is passed 

 through within the area. If such be so, problems concerning the 

 maintenance of the stock are much simplified. 



The present contribution does not deal with the entire spawning 

 period on the Scottish Coast, but it is desirable even at this stage to 

 review the facts already elucidated for a part of the season and to con- 

 sider their bearing. So often has the problem been attacked by in- 

 vestigators, more particularly by Scottish workers, and so numerous 

 have their publications been that it is almost impossible to acknowledge 

 briefly one's indebtedness to individual writers. Special reference must 

 be made to contributions on this subject by Dr. Fulton, especially 

 to his work on the relation of the currents of the North Sea and their 

 bearing on the spawning of the common food fishes. 



SPECIAL REFERENCES. 



Numerous papers published in the Annual Reports of the Fishery 

 Board for Scotland by the following : — Fulton, Masterman, M'Intosh, 

 Kyle, Williamson, Dannevig. 

 1899. Heincke, Fr., and Ehrenbaum, E., " Eier und Larven von Fischen 



der Deutschen Bucht " ; Biolog. Anst. auf Helgoland. 

 1909. Ehrenbaum, E., "Eier und Larven von Fischen" ; Nordisches 



Plankton. 

 1909. Brown, Captain C. H., " Report on the Deep Currents of the 

 North Sea as ascertained by Experiments with Drift 

 Bottles " ; 



Fourth Report (Northern Ai'ea), on Fishery and Hydro- 



gTaphical Investigations in the North Sea and 



adjacent waters. 



1913. Thompson, Prof. D'Arcy W., " Observations on the Plaice " ; 



Fifth Report (Northern Area), Fishery Board for Scotland. 



1913. Fulton, Dr. T. Wemyss, " Report on the distribution and 



seasonal abundance of flat-fishes {Pleuronectidae) in the 



North Sea, and the fluctuation in their abundance during the 



years 1901-1910 " ; 



Fifth Report(Northern Area), Fishery Board for Scotland. 



