6 FISHES AND FISHERIES OF THE IRISH SEA. 
3. Rivers AND ESTUARIES. 
The chief rivers entering the Irish Sea are :—The Nith, the Annan, the Esk, and the 
Eden, falling into the Solway Firth ; the Derwent, and the Duddon, in Cumberland ; the Lune, 
the Kent, the Leven, and the Wyre, entering Morecambe Bay; the Ribble, at Preston ; the 
Mersey, at Liverpool; the Dee, at Chester ; the Clwyd and the Conway, in North Wales ; 
the Dovey and the Teify, in Cardigan Bay; and the Slaney, the Liffey, and the Boyne, 
on the east coast of Ireland. All of these, and some smaller ones (23 in all in our Sea 
Fisheries District) are salmon rivers; and the Ribble, the Mersey, and the Dee form 
important estuaries in Liverpool Bay. 
None of these rivers are, however, of very large size, no great volume of fresh 
water enters the area, and consequently the specific gravity, except actually in the estuaries 
and at the mouths of the streams, is relatively high, being generally at least 17025. 
4. TEMPERATURE. 
The temperature of the sea-water, of course, varies much in the district, according 
to the depth, the locality, and the season. The temperatures of air and sea-water have 
been taken with regularity twice a day for years at the Marine Biological Station—at first 
on Puffin Island, and for the last 10 years at Port Erin. 
The lowest temperature recorded in winter is 37° F. in February, 1898 and 1goo, and the 
records show clearly how, during the greater part of spring and summer, before the maximum 
has been reached, the temperature of the sea lags behind that of the air, until, in September, the 
air approximates to, and then begins to be colder than the sea. The highest temperature 
we have recorded in-summer is 72° F. on August 15th, 1893, but that was exceptionally 
high. The following summer the highest record was 62° F. These records are for the 
open bay. Of course, in shallow water on the shore, on some days, the temperature is 
higher than the above. On several occasions in front of the Laboratory it has reached 76” F. 
During March and April, while fish hatching was going on, the water in the hatching- 
boxes at Port Erin was found to range from 50 to 53 F., with a specific gravity of 
from 1°0265 to 1°0270; while at Piel, in the Barrow Channel, at the same time of year, 
the records are from 39° to 41° F., with a specific gravity of 170258 to 1°0268. 
In the year 1898, at Port Erin, the temperature of the sea in January was nearly 
uniformly 2° F. higher than that of the air, while in February it averaged 4° to 5° F. higher. 
In March it was about 3° higher, and in April the difference was reduced tor F. From 
May onwards, the air is occasionally as high as or even higher than the sea, and in August 
and September they generally average the same. Then the air temperature begins to fall 
again below that of the sea. 
5.—SPECIFIC GRAVITY. 
The average specific gravity at Port Erin is about 1.0260. 
The following samples were taken in different parts of the district, in October and 
November, 1gor1, and were examined in the Zoological Laboratory, at University College, 
by Mr. Alfred Holt, jun., who is preparing a detailed paper upon these and other 
samples, which will be published in the Fisheries Laboratory Report for 1901. The value 
of the last place of decimals may be altered in some cases in that fuller paper. 
