SEA- FISHERIES LABORATORY. 191 



is only indicated approximately by the differences in length, 

 for there is a considerable variation in the sizes (or ages) at 

 which plaice become mature. The meaning of these differences 

 in the migration paths taken by the fish is therefore this : the 

 plaice that are approaching the stage of sexual maturity move 

 offshore, into deeper water, and towards the spawning grounds 

 in St. George's Channel and in the Solway, while those which 

 are still in the immature condition migrate back again to the 

 nursery grounds. 



(2) The Red Wharf-Beaumaris Bay Experiments. 



Looking at the results of the marking experiments con- 

 sidered so far we see two rather singular things : (1) Year 

 after year a certain fraction of the plaice that have migrated 

 offshore from the nursery grounds in the summer return there 

 again in the autumn and winter months ; (2) Year after year 

 a certain fraction of the plaice that have migrated from the 

 nursery grounds into the Red Wharf-Beaumaris Bays region 

 also return in the winter months. What becomes of the plaice 

 that do not so return ? This question was investigated by 

 marking and liberating several lots of fish on the grounds 

 near Red Wharf Bay during the course of the back-end fishery. 

 These experiments were : — 



12th Nov., 1904 42 plaice. 



Do. 49 „ 



24th Oct., 1907 120 „ 



20th Nov., 1913 220 „ 



Total ... ... 4)31 plaice. 



First, we take the experiments made in October and 

 November: 431 plaice were liberated, and 106 of these were 

 reported as recaptured on the same grounds as those on which 

 they were Liberated — that is, within a line drawn straight from 



