SEA-FISHERIES LABORATORY. 293 



along the line of Stations 1 to 4 is abont 5° to 8°; that 

 from Nelson Buoy to BahamaBank is about 4° to 7° ; while 

 that from Nelson Buoy to Red Wharf Bay is about the 

 same. Off the Estuaries of the Ribble, Dee, and Mersey, 

 the gradient is steeper still : this is the coldest part of 

 the whole Irish Sea in winter, with the exception of the 

 upper reaches of the Solway Firth. Centrally the 

 gradients are small, and the temperature is very uniform 

 over a wide area. So much can be deduced from the 

 incomplete observations of February, and the general 

 trend of the isotherms, while subject, no doubt, to slight 

 alterations, will probably remain the same when all the 

 observations are obtained. 



The period of maximum temperature is represented 

 by Chart IV, which represents the conditions on 

 15th August, 1912. The highest temperatures, about 

 16° to 17°, are now found close in-shore, and the lowest 

 in the central sea-area south from Isle of Man. The 

 gradients are fairly steep, and lines drawn normal to the 

 isotherms would run approximately at right angles to the 

 general trend of the coast line, since the isotherms run 

 roughly parallel to the latter. So far as the latter 

 indicate the direction of inflowing water, this appears to 

 be more towards the sea between Isle of Man and North 

 Lancashire, than round Anglesey into Liverpool Bay. 



III.— Temperature Conditions and Fish Migrations. 



The general conditions existing in the Irish Sea 

 during the summer of 1912, and the winter of 1912-13 

 are represented in the Tables and Charts which have been 

 discussed. Summarising them, it may be stated that the 

 differences in temperature in different parts of this area 

 are relatively considerable at two periods of the year, 

 (1) the months December to February, when the sea is 



