236 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



just outside the territorial limits in Liverpool Bay (Col. 1 of 

 Table 26), and these fish also were unusually small. Now 

 these grounds were not worked in the corresponding months of 

 any of the previous years, and so (just because of this difference 

 in the sampling methods) the size of plaice on the " North-west 

 Coast region " would have appeared to have diminished in 

 1920 as compared with previous years. Therefore we must 

 distinguish, to a rather fine degree, between the various grounds, 

 and we must compare, with each other, only rather small areas. 

 Even then there are " accidental " variations that might 

 mislead us. Thus a good breeze of wind may make a 

 perceptible difference in the kind of plaice found on a ground 

 in the course of a few days. We have seen, however, 

 that it is not the difference in the rate of growth that 

 makes the fish on a ground appear to be bigger in some 

 years than in others, but rather the varying proportions of 

 older and younger plaice. That means, then, that more fish 

 are spawned, transformed, and reared (one or all) in some 

 years than in others, which means, again, that some years are 

 more productive than others. So there is a good deal to be 

 made out of the length measurements— if we are critical. 

 If only we had had good series of plaice measurements in 1889 

 (when the regulation began in Lancashire) the questions pro- 

 pounded now would have been more easily answered. Perhaps 

 this is the most convincing argument for the future utility of 

 the series of measurements recorded in this report. 



Is there an " Accumulated Stock " ? Does Increased Fishing 

 tend to make the Fish run smaller? 

 An " accumulated stock " of plaice means that the fish 

 grow old more rapidly than they are caught. There is no 

 accumulated stock in Liverpool Bay because the plaice migrate 

 out from this region as they grow old. But even if the natural 

 conditions were such that plaice of five or more years of age 



