186 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



ten- and twenty-fathoms' contour lines. From regions (1) 

 and (2) the plaice are still moving closer inshore, and from 

 (3) they are moving down into the Ked Wharf-Beaumaris Bay 

 area. A new path is clearly indicated — that from the grounds 

 just offshore from the original area of liberation up to the 

 banks offshore from Ramsey Bay, in Isle of Man. 



The Autumn and Winter Migrations. 



We may now summarise the results obtained so far : these 

 are represented in Fig. 14 in a very general way. Each arrow, 

 tipped with a black dot, represents the approximate position 

 of an actually-recaptured marked plaice, while some other, 

 untipped arrows on the chart merely suggest the general 

 directions of the migrations. All the marked fish recorded as 

 recaptured in this chart were liberated in the region indicated 

 as the " area of liberation " in Figs. 8 to 13 : this is the 

 region in Fig. 14 where the tipped arrows are most densely 

 crowded. 



First, then, we have the summer offshore migration. 

 The plaice, of sizes about 20 to 25 cms., stream outwards from 

 the Lancashire coast to the S.W., W., and N.W., and by the 

 end of August they have come to occupy a region of sea, just 

 outside the ten-fathom contour line and extending from about 

 Morecambe Bay Light Vessel down to Liverpool N.W. Light 

 Vessel. There is an active plaice fishery all over this region, 

 while outside it and up to the N. and N.W. there is also an 

 active fishery for soles. This offshore migration, then, is the 

 first half of the total migratory movement of Lancashire shore 

 plaice. 



Next, there is a retrograde movement, and this reversal 

 occurs about the time when the temperature of the sea, having 

 attained its annual maximum, is now beginning to decrease 

 again. The retrogression is indicated by the successive contour 

 lines — " September- October," " November-December," and 

 " January-February." Each of these lines is a boundary, 



