90 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



this work in May of 1921, when the sole spawning season 

 occurs. 



I have made a report on these results and have incorporated 

 in it a summary oi the Irish Sea plaice investigations carried 

 on by the Committee during the years 1908-1913. This enables 

 one to make a comparison between the post-war year 1920 

 and the pre-war period. When that has been done it becomes 

 evident that the marked increase in the abundance of large 

 plaice which characterises the Irish Sea no less than the North 

 Sea grounds need not be due to the partial cessation of trawling 

 brought about during 1913-18 by the wartime restrictions. 

 In last year's report Mr. Daniel summarised the results of the 

 very valuable series of trawling experiments made during the 

 years 1890-1920 by Captain G. Eccles. These relate to a very 

 typical " small-plaice " fishery ground, that off the Mersey 

 Estuary, and they show an evident periodicity hi the abundance 

 of plaice in this region. During the years 1895-6 plaice were 

 very abundant, and the same was the case during the years 

 1909-10. Again plaice were relatively very scarce during the 

 years 1905-6 and 1915-16, so that during the time in which 

 the Committee has been in existence there have been two. 

 cycles of abundance and poverty of plaice. I have shown, 

 also, that there are very marked differences from year to year 

 in respect of the proportion of baby plaice of six to twelve 

 months old that are taken in the shrimp trawl-nets. This 

 means that in some years great numbers of the plaice fry that 

 have hatched out in the Irish Sea die — probably because there 

 is, in tnose years, insufficient planktonic food in the water about 

 the time when the fry are pelagic — that is, before they sink 

 down to the sea-bottom as completely formed little flat-fish. 



So when one allows for this periodicity in the abundance 

 of plaice on the fishing grounds it is not at all certain that the 

 effect of the wartime restrictions on trawling was to increase 

 the natural stock of the larger sizes of plaice. It may merely 





