SCIENCE AND THE SEA FISHERIES 241 



The marking experiments also give some indication of the great 

 intensity of fishing on the North Sea grounds. Owing to the fact 

 that many of the fish are injured in the trawl when they are caught, 

 and hence do not survive after they have been marked and liberated 

 and also to the fact that the labels used for marking appear to drop 

 off the fish after about two years, the estimate of the intensity of 

 fishing yielded by the experiments is a minimum one. 



In some of the experiments in which special precautions were 

 taken to mark only healthy and vigorous fish, the percentage 

 returned within one year of liberation has reached 50 per cent. 



In their Irish Sea experiments the Lancashire Committee en- 

 deavoured to obtain information on three points ; the migration 

 of the plaice, their rate of growth, and the intensity of fishing on 

 the different grounds. In the case of individual fish remarkable 

 journeys were performed. Of a batch of fish liberated off Blackpool 

 two were recaptured on the east coast of Ireland, one in Courtown 

 Bay the other at the La5rton Coastguard Station. These fish must 

 have travelled at least 130 miles in six months. In the case of 

 another batch of fish marked and liberated in October in Beaumaris 

 Bay, one was recaptured by an Ostend steam trawler, the Jules 

 Henri, in 48 fathoms water near the coast of Waterford the follow- 

 ing May, and another in the entrance to the English Channel by 

 the Fleetwood steam trawler Eulalia the following September. 

 In one case a fish was caught three times in a few months. It was 

 first caught, marked and liberated near Morecambe Bay Lightship. 

 Ten weeks later it was again caught by one of the Lancashire 

 Committee's cutters in Barrow Channel, and returned to the sea 

 alive. Hardly a month elapsed before it was again caught, this 

 time by a Fleetwood fisherman. The intensity of fishing in certain 

 areas off the Lancashire coast must be extremely high. On the 

 other hand, some fish have only been recaptured after two years. 

 A plaice marked and liberated off Walney Island was caught over 

 two years later, eight miles south-east of the Bahama Lightship 

 (off Ramsey Bay, Isle of Man). In another case a plaice marked 

 and liberated off Llanrhystyd, in Cardigan Bay, was found two yean, 

 afterwards only a few miles away at Llanon. In a third instance 

 a plaice marked and liberated off Penkilan, in the county of Car- 

 narvon, was recaptured after two years 3 miles west by north of the 

 Barrels Lightship, Wexford. 



In spite of many remarkable journeys, the plaice of the Irish 

 Sea must be regarded as, on the whole, sedentary creatures. The 

 Irish Sea is really comparable to a large lake with an indigenous 

 fish population ; and probably derives little by immigration from 

 other waters, except in the case of certain pelagic species, such as 



