115 



The following explanation will serve for this, and the 

 other charts illustrating the migrations. Each recapture is 

 indicated by a black dot, and the number underneath the latter 

 gives the length of the fish, as recaptured, in centimetres. 

 The area where the fish were liberated is outlined by a broken 

 line enclosing the words " area of liberation." An irregularly- 

 curved contour line, marked " June and July," is drawn round 

 the places of recaptures in these two months so that we may 

 understand that the fish liberated have spread out, in all 

 directions, from the " area of liberation " to the area enclosed 

 by the " June-July " boundary line. During June and July, 

 plaice previously inhabiting the shallow-water region 

 immediately offshore are migrating out to the West, North-west, 

 and South-west from shallower into deeper water, and from a 

 warmer into a colder region of sea. 



Certain temperature contour lines are drawn on the chart, 

 but these will be explained later on. 



The August Migrations. 



It is fair to assume that all the plaice caught and liberated 

 on the " area of liberation " in June and July have now left 

 that region and have migrated outwards as just explained. 

 No recaptures are reported from the " area of liberation " in 

 August, though there was plenty of fishing going on there, 

 and this means that during June, July, and August there is a 

 continual streaming out of plaice from the Ribble Estuary, 

 and all the adjacent nursery grounds. As the plaice grow up 

 to about 20 cms., or thereabouts, in the summer months, they 

 abandon the nurseries for the more open sea offshore. The 

 chart shows an irregular area marked by the dotted line 

 " June- July " : this was the region where the marked fish 

 were recaptured in those months. A number of black dots 

 are seen in this area and to North and South of it, and 

 these are the positions of recaptures in August. Therefore the 

 plaice, which were within the " June- July " boundary in those 



