53 



And the proprietors of such fisheries, throughout the coun- 

 try, may expect, that as the district is improved, the pro- 

 duce of their fisheries will diminish. 



In connection with this part of the subject, and as a 

 striking illustration of what has been said, the case of the 

 Cocket, a small river in England, may be noticed. The 

 produce of the Salmon-fisheries in the Cocket, was at 

 one time very considerable. But, all at once, it was found 

 that the fish had deserted the river. This at first excited 

 some surprize ; but it was soon discovered that the change 

 was occasioned by the operations and ingredients used at 

 one single tin manufactory in the upper part of the river. 

 The water had in consequence become impregnated with 

 deleterious matter ; and hence, although a coarse species 

 of trout still frequented the river, not a Salmon would 

 enter it. * 



It is clear, therefore, that, any diminution in the pro- 

 duce in particular rivers, may be accounted for from causes 

 very different from a decrease in the number of the fish. If 

 the Thames, the Cocket, &c. were restored to their former 

 state of purity, the Salmon would again frequent them. 

 But so long as they continue in their present state of pol- 

 lution, Salmon will not enter, unless compelled by disease, 

 or some such cause. The fish naturally seek more salubri- 

 ous waters, and, according as these become insalubrious, 

 they will desert them. 



If, indeed, it could be shewn, that, in rivers not affected 

 by any noxious change, there has been an unequivocal fal- 



* This is stated on the authority of a highly respectable and 

 intelligent fisher, who visited the Cocket almost immediately 

 after the change took place. 



