230 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



that and 1914 is only a very short period. The conditions, then, 

 that have been observed in the North Sea are consistent with 

 the belief in a natural fluctuation as capable of explaining, 

 to a certain extent, the variability, from year to year, in the 

 productivity of the fishery. 



" To a certain extent " only, we may add. Probably the 

 Irish Sea is a more productive area, as far as plaice is concerned, 

 than the North Sea. The " productivity " depends on the 

 existence of the shallow- water nurseries. Just because the area 

 of such grounds is greater in the Irish Sea, relative to the 

 total area of sea, so we expect a greater production of plaice. 

 Probably the exploitation of the North Sea, that is, the amount 

 of trawling per square mile, per year, is greater than it is in the 

 Irish Sea. If that is so then the natural fluctuations that we 

 are assuming would be more easily noticeable in the eastern 

 than in the western region, particularly if, as may be assumed, 

 the exploitation in the North Sea is pressing closely on the 

 recuperative power of the nurseries. 



It is quite unlikely that the data exist which would enable 

 us to answer the questions suggested above. The fishery 

 statistics are too imperfect prior to 1908 ; the work of com- 

 parison of the productivity of the fishing grounds before and 

 immediately after the cessation of war was not thorough enough, 

 in any British fishing ground ; we have no available knowledge 

 of the extent to which military restrictions actually prevented 

 fishing in the various regions ; no detailed classification of the 

 " plaice fishing grounds " that is of much use, and, of course, 

 not nearly enough knowledge of the life-history of our species 

 of fish. It is regrettable that the opportunity for studying 

 the very remarkable conditions that the war-restrictions 

 afforded was not taken full advantage of in 1918 and 1919 

 by any European fishery authority. 



