SEA-FISHERIES LABORATORY. 459 



the channel near Lytham; and a bed in the Pibble 

 channel close to the training wall and nearly opposite 

 Ansdell. The cockle beds are very numerous and 

 important. They occur over a great part of the lower 

 part of Horse Bank sloping down Pinfold channel, 

 on the "Brow," that is. They also occur over a great 

 part of Salter's Bank, mainly to the east of the New Gut 

 Channel. These cockle beds vary greatly in their precise 

 position from year to year. Spat falls and new beds of 

 small cockles are formed, and are fished when the shell- 

 fish attain legal size. Also old beds become sanded up 

 by the shifting of the banks and channels, or by heavy 

 seas. 



The pollution of the shellfish is not so great as might 

 be expected, considering the enormous volume of sewage 

 which enters the estuary. This is partly due to the 

 enormous dilution which the sewage undergoes, and 

 partly to the fact that the greater part of this — the 

 Preston, Southport and Birkdale sewage — is treated 

 before entering the sea. " Our general impression," say 

 the Royal Commissioners on Sewage Disposal, "of the 

 whole Pibble estuary was very favourable. In spite of 

 the extensive and populous district draining into it, and 

 the varied industries contributing their trade effluents, no 

 marked indications are to be found, even a few miles 

 below Preston, while at Lytham all signs have dis- 

 appeared." (Report V., Appdx. VI. [cd. 4284]. 1908.) 

 We see here, as also in the case of the mussel beds at 

 Morecambe, the conditions that obtain when even an 

 enormous volume of sewage enters a wide estuary, almost 

 an open sea area, in contrast with the conditions that 

 are exhibited when a very much smaller volume of sewage 

 enters a narrow estuary, as in the case of Barmouth, 

 Aberdovey and Conway, in Wales, and the Lune, in 

 FF 



