202 BULLETIN OF THE BUREAU OF FISHERIES. 



Table 2. — Rate op Growth op Mussels on Wharf Pile, Woods Hole, Mass., in Millimeters. 



Table 3 indicates the rate of growth of mussels on a mud bottom at the mouth of 

 Menemsha Pond, Marthas Vineyard, Mass. A rather strong tidal current of water, 

 rich in food matter, swept back and forth over them with but a few minutes of slack 

 water prevailing at each turn of the tide. They were exposed only when the tides 

 were extremely low. Alga and eelgrass grew about them to considerable extent, but 

 they were at no time covered with the vegetation. In this situation growth took place 

 at about three times the rate of that in the Pine Island mussels. 



Table 3. — Rate of Growth of Mussels in Menemsha Pond, 



in Millimeters. 



Marthas Vineyard, Mass., 



Comparison of these results with those of Williamson (1907) show that they are 

 almost identical. The least amount of growth observed, 4 mm. or one-seventh inch, 

 compares favorably with Williamson's one-eighth inch minimum increase, while the 

 10.5 mm., or nearly seven-sixteenths inch, compares well with his three-eighths inch 

 maximum growth. 



These results, however, should not be taken to mean that the rate of growth of the 

 sea mussel is from one-fourth to one-half inch per annum, for specimens are often found 

 which show an annual growth of 1 inch or more. It is not uncommon to find mus- 

 sels 3 inches long on beds which are from three to four years old. Orton (1914) reports 

 that the Plymouth (England) mussels attain a length of from if to 2 inches the first 

 year and when 18 months old average 2 inches long. In France, where they are culti- 

 vated on wooden frames, the mussels attain a length of from \% to 2 inches in from 12 

 to 15 months. At Woods Hole, Mass., ropes on fish traps put out in April and taken in 

 the last of August were found covered with young mussels, many of which were nearly 

 three-fourths of an inch long and which could not have been more than 4 months old 

 (fig. 189). Less rapid growth has been found to occur in the older shellfish. Wright 

 (1917), after careful examination, has shown for the mussels of Cardigan Bay that the 



