84 BULLETIN OF THE BUREAU OF FISHERIES. 



able situation. Distribution by currents presumably has little practical effect, except, 

 perhaps, in the case of such a thin-shelled species as Anodonia imhecUlis. 



DENSITY OF POPULATION. 



Strange stories are heard of the density of mussels in beds. It has been said that 

 the living mussels in certain beds were in a layer 2 feet deep. Such stories, persistent 

 among clammers, are, of course, based upon faulty reasoning. A bed is gone over 

 repeatedly with crowfoot bars, and with continuing success, but the fact is overlooked 

 that the appliance takes mussels only at random. A layer of mussels is not moved at 

 each drag. A particular bed in the Mississippi River, more than a quarter of a mile 

 long and 100 yards wide, was insistently described as being uniformly 2 feet deep in 

 mussels. Further inquiry elicited the informat'ion that the bed was virtuallv cleaned 

 up in a season and that about a half dozen carloads of shells were obtained. A simple 

 calculation showed that, had the bed been as described, at least 30 trains of 100 cars 

 each would have been required to move the shells obtained. Other stories relate to 

 such observations as the taking of mussels by suction dredges after excavating deep 

 holes in the bottom, no consideration being given to the possibility of a mussel falling 

 in with the caving sand from above. 



In planting operations and in experiments involving the retention of mussels for 

 considerable periods, if normal health and growth are desired it is important to know 

 how closely mussels may be crowded. The following observations are therefore offered. 



The place of densest mussel growth observed by the senior author in the Grand 

 River, Mich., in 1909, yielded 52 living mussels of 6 species from a space 6 feet long by 

 3 feet wide, giving a density of about 3 mussels per square foot. Clark and Wilson 

 (191 2, p. 20) found a most favorable place for observ'ations of density in the Feeder 

 Canal, near Fort Wayne, Ind., which had been recently drained. The bottom of the 

 canal had been abundantly populated with mussels and from i square meter they took 

 81 mussels of 8 species, or about 7K per square foot. At the place of greatest observed 

 density in the Clinch River, Tenn., J. F. Boepple took 66 mussels of 10 species from an 

 area which he estimated to be 4 square feet; if his estimate was correct, the density 

 was 16^ per square foot. 



At all of these places mentioned, mussels occurred in such striking and unusual 

 abundance as to suggest to experienced observers the desirability of making actual 

 counts. It is fair to assume, then, that the natural occurrence of more than three or 

 four mussels per square foot over any considerable area is unusual and that plantings 

 of large mussels in greater density are warranted only where the conditions are shown 

 to be particularly favorable. 



Very small juveniles may safely be planted more closely. Howard reared for a 

 season 217 juveniles in a floating crate 18 by 24 inches, but the rate of growth among 

 them was very variable. (Pl.V, fig. 3.) In other rearing experiments at Fairport (con- 

 ducted by F. H. Reuling) 2,006 juvenile sand-shells were obtained from a trough 14 

 feet long and i foot wide, a density of 143.3 per square foot. In another trough of the 

 same size, 3,016 juvenile Lake Pepin muckets were reared, a density of 215.4 P^r square 

 foot. It is not to be assumed, however, that the young mussels would have lived long 

 and grown normally while crowded so closely as were these. 



