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evidently the cod fish had swallowed the clams five and six 

 at the time, digested off the contents, and the shells had 

 been piled up in this way in their stomachs for compact- 

 ness of stowage and ejected. These clam-shells had been 

 picked up by 100 bushels at the time ; but the fishermen 

 also watched the food of the mackerel, and followed them 

 along the coast very largely in advance of their movements. 

 This was principally crustaceae. They followed the crus- 

 taceae along the coast, not so much by seeing it, because it 

 was too small to be readily seen, but by watching small 

 birds, sea geese as they called them, which fed on these 

 crustacese, whenever they noticed them they knew that if 

 they set their bait for mackerel they would be likely to be 

 successful. An interesting point which arose from the 

 observations of fishermen was the relation which different 

 kinds of fish had to each other, and the changes in the 

 distribution of different species depending on this question of 

 food. About twenty years ago mackerel was very abundant 

 in Massachusetts Bay, but suddenly there appeared great 

 shoals of blue fish, fish of, say, 16 to 20 Ibs., exceedingly 

 predaceous, which destroyed all other fish in great numbers. 

 That fish which had been absent from the coast for many 

 years made its appearance suddenly round Cape Cod, and 

 before this the mackerel vanished, and the mackerel fishery 

 decreased exceedingly ; but at the same time there was a 

 corresponding increase in the lobster fishery. No one 

 knew what to make of it until a very acute old fisherman, 

 Captain Attwood, went to work and studied the subject, 

 and he demonstrated pretty plainly that the absence of the 

 mackerel had had the effect of increasing the number of 

 lobsters, because the mackerel were in the habit of feeding 

 on lobster eggs. The blue fish destroyed the mackerel, 

 and that gave the lobsters a chance to breed. Now the 



