MARINE ZOOLOGY 



both the Ribble and Wyre, and the fresh water carried down by these rivers 

 was, even a week later, floating at the surface of the sea in admixture with 

 normal sea water. 



The characteristic marine fauna of the Lancashire inshore waters is the 

 result of these physical conditions — the shallow depths, the extensive sand and 

 mud deposits, the rapid tidal streams and the great rise and fall of the tides, 

 and the somewhat low salinity due to river water. While these conditions 

 produce a fauna which to the marine zoologist is somewhat lacking in variety, 

 and may be described as commonplace, they have at the same time made the 

 Lancashire inshore waters and the foreshore between tide marks one of the 

 most valuable inshore fishing grounds round the British Islands, and one 

 which presents many features of interest. 



Shellfish beds are thickly distributed over the whole of the Lancashire 

 coast, and the cockle fishery of Morecambe Bay is without exception the 

 most valuable round the British Islands, while some parts of the coast yield 

 mussel fisheries not much less important. Practically the whole of the northern 

 part of Morecambe Bay consists of cockle-bearing sands. Here and there over 

 this extensive area, and also at the mouth of the Ribble estuary and out from 

 the Mersey along the Lancashire coast from Liverpool to Formby Point, cockle 

 beds are abundantly distributed. The exact positions of these beds are always 

 changing, for the formation of such a shell-fish bed depends on the deposit of 

 the cockle ' spat ' or ' seed ' — that is the minute free swimming larvas of the 

 mollusc. During the spring of the year the cockle spawns, and after a week 

 or two the eggs so produced develop into larv£e provided with ciliated 

 swimming organs. These larvae are borne in the water by the tides and 

 currents, and the place where they settle down depends on the winds, tides, and 

 other conditions. When they do settle down in the sand a cockle bed is pro- 

 duced and sometimes an incredible abundance of these shellfish results, so that 

 the moUuscs may actually smother each other. In a few months these shell- 

 fish may grow from half an inch in diameter to nearly twice that size and 

 become big enough to be taken by the fishermen. Walking over a cockle bed 

 one does not at first see many signs of the presence of these bivalves, for they 

 are buried in the top layer of the sand with only the tops of their siphons pro- 

 jecting, presenting the appearance of a pair of small dark holes (the ' eyes ' of 

 the cockles). Sometimes a tuft of algae attached to the posterior end of the 

 shell betrays the presence of the mollusc, and the appearance of the ' groats ' (a 

 north Lancashire term) also indicates where a cockle lies hidden. The 

 ' groats ' are the extruded strings of fascal matter lying on the surface of the 

 sand. Few people have any idea of the value of this humble mollusc to the 

 Lancashire fishermen, and it will surprise most to learn that from five to 

 ten thousand tons of cockles may be taken annually from the Lancashire 

 foreshores. 



The habitat of the mussel is somewhat different from that of the cockle. 

 While the latter mollusc lies buried in the sand and unattached to any sub- 

 stance, the mussel lives above the surface and is attached to stones, etc., by 

 means of its byssus. In almost every case a deep deposit of mud, sometimes 

 several feet thick, may be formed between the layer of mussels and the solid 

 substratum of stones or gravel, etc. (the mussel 'skear'), to which the molluscs 

 are attached, this process being accompanied by the gradual lengthening of the 



I 89 12 



