60 TJ. S. BUREAU OF FISHERIES. 



The Florida hard clam (Venus mercenaria mortoni) bears a close 

 resemblance to the New England quahaug (V. mercenaria). It 

 is difficult to separate the two varieties when comparing specimens 

 3 or 3^ inches in length, but in general the southern clam attains a 

 larger size and has a thicker and heavier shell. It is not unusual to 

 find these clams weighing more than 2 pounds each. About 125 

 clams of average size fill a 5-peck basket, and as a full basket weighs 

 about 125 pounds the average weight of a clam is 1 pound. 



The clams may be divided into three types, although they all be- 

 long to one species. There is a thick-lipped type, a thin-lipped type, 

 and an intermediate type. The thick-lipped clams are sometimes 

 known as " bullnose," and are said to be somewhat inferior to the 

 thinner-lipped variety. The shell of the thin-lipped clam is some- 

 what lighter than that of the " bullnose," but it is heavier than the 

 shell of the northern quahaug. It is probable that the thickness of 

 the shell at the lips is due to some extent to age and retarded growth, 

 but the fact remains that small thick-lipped clams may be found in 

 places where the clams are scattered, and large thin-lipped ones are 

 found where clams of all three types are exceedingly abundant. The 

 relative abundance of each type, judged by the averages obtained 

 from numerous examinations made in various parts of the great clam 

 bed, is as follows: Thick-lipped, 50 per cent; thin-lipped, 30 per 

 cent ; and intermediate, 20 per cent. The average size of 50 thick- 

 lipped and 50 thin-lipped clams selected at random was 3| inches 

 for the former and 3^ inches for the latter variety. Measurements 

 were taken with calipers, the points of which touched the hinge liga- 

 ment and the farthest opposite point. Measured in this way about 

 95 per cent of the clams, whether dug by hand pickers or dredge, 

 ranged between 2^ and 5 inches in length. 



Dead clamshells are found almost everywhere on the clam beds. 

 In some places they are very abundant, while in others they are 

 occasional. It is said that the clam dredge kills many of the clams, 

 but this is improbable for the following reasons: (a) The dead 

 shells are found over almost the entire bar; (b) the dredge has 

 worked over but a small portion of the clam bar and only in two or 

 three restricted localities: (c) nearly all the shells are unbroken, 

 while many of them would likely be mutilated had the dredge been 

 responsible; ((I) the writer dug several hundred clams in a locality 

 where the dredge certainly never had operated and found many dead 

 shells; and (e) sometimes a single valve was lying flat on the bottom 

 and sometimes the two valves were intact and filled with mud but 

 were buried in the same position as when living. 



It is but natural that many clams should die where their numbers 

 are vast and when they live in a region almost untouched by man. 

 Like all living things, clams must die at some time of old age, if 

 for no other reason, and this may be responsible for the presence of 

 many dead shells. Sudden changes in the salinity of the water may 

 also cause a part of the mortality. Fresh water supplied by the 

 numerous small rivers of the Ten Thousand Islands lowers the 

 density of the water on the clam bar, particularly during the rainy 

 season. This brackish condition of the water is especially suitable 

 for the growth of the clams. During the winter, however, when rains 

 are very infrequent, the density of the water increases until it is 

 equal to that of Key West or other points not affected by fresh water. 



