SEA- FISHERIES LABORATORY. 235 



of late (except during the war years). The number of steam 

 vessels working from Fleetwood has increased, and though 

 most of these vessels fish outside the Irish Sea region it is 

 likely that much about the same fraction of all of them trawl 

 on these grounds each year. The number of smacks working 

 from Fleetwood and Hoylake has steadily decreased since about 

 1890, and there are no indications that the number of half- 

 decked sailing boats has increased. But the increase in 

 number of the steamers probably makes up for the decrease 

 in the smacks and the decrease ("if any ") in the small boats. 

 Probably, then, the catching power is approximately uniform 

 or has increased. 



So far as the commercial statistics go they show that 

 there are marked ups and downs in the quantities of plaice 

 landed from the Irish Sea. There was a maximum in 1911, 

 a minimum about 1915, and another maximum about 1920. 

 Thus there is no definite tendency one way or the other, so 

 far as these data enable us to discuss the question. 



So far as the experimental trawlings go the same conclusion 

 is to be made. There are ups and downs, and these are nearly 

 the same as the changes revealed by the commercial statistics. 

 In fact these two series of data support each other to a certain 

 extent and indicate that there have been actual changes in the 

 natural productivity of the Irish Sea grounds during the period 

 1908-1920. 



When we deal with the measurements of lengths of plaice 

 caught on the fishing vessels (steamers and smacks) and caught 

 experimentally there is rather more trouble, because there are 

 so many ways of going wrong in our deductions. " Lumping " 

 of the various grounds in even such a small region as the Irish 

 Sea is fatal. In the winter of 1920, for instance, a fairly large 

 number of plaice were measured on the Sol way grounds and 

 these were all rather small fish (see Tables 26, 27). Also 

 2,275 plaice were measured on board a steam trawler working 



