SEA-FISHERIES LABORATORY. 125 
January and February. 
The in-shore migration to the coasts of Lancashire and 
Cheshire continues. So also does the off-shore migration 
to the north-east of Isle of Man. But the westerly migration 
into North Wales area ceases very suddenly in January. 
(6) Length of Fish, and Migration paths. 
We must now note the characteristic sizes of the plaice 
taking part in these migrations. The plaice that migrate 
into the Lancashire and Cheshire shallow waters in the winter 
are “ small,” that is, 50 per cent. are between 214 and 25 cms. 
The fish that migrate into the North Wales area deeper 
waters may be called “medium”: 50 per cent. of them are 
between 23 and 26 cms. 
The fish that migrate towards the north-east of Isle of Man 
are “large”: 50 per cent. are between 25 and 284 cms. 
(7) Seasonal, Feeding and Spawning Migrations. 
These are the kinds of migration exhibited by plaice 
in the Lancashire off-shore area. 
Seasonal migrations are undoubtedly determined by the 
change of temperature of the sea-water during the year. 
It would take too long to elaborate this point, which is, however, 
quite clear and certain from our accumulated observations. 
Feeding migrations are brought about by local aggregations 
of food on the sea bottom, as, for instance, the formation 
of a bed of growing mussels (see the instance given by Scott 
in the Quarterly Report for October, 1913). These are not 
migrations in the strict sense, but rather local and temporary 
ageregations of plaice. 
Spawning migrations have little importance in the 
Lancashire area, as the plaice are mostly immature. The 
larger fish that migrate towards the north-east of Isle of Man 
do so in order to spawn there. The larger plaice found off 
the coasts of North Wales in the months of November and 
