18 PROTECTION OF FRESH-WATER MUSSELS. 



nating every possibility of uncertainty or difference of opinion. Mus- 

 sels are sometimes measured in length or width or height, but on 

 account of the irregular form of mussel shells these dimensions are 

 not always interpreted in the same way. In testing the blank-making 

 capacity of a shell, commercial men sometimes measure the " width 

 on the face " ; that is, between the lateral hinge tooth and the lower 

 margin of the shell. This measure can of course only be taken from 

 an open shell, and therefore could not serve for our purpose. It is 

 worth while to call attention to the fact that a 2-inch shell as meas- 

 ured in greatest dimension would be a good deal smaller than a 

 2-inch shell in commercial measurement. 



An inspector would need to be equipped with an ordinary rectan- 

 gular caliper. If a shell should be found to measure more than 2 

 inches in any linear direction it would be considered as above the 

 size limit. 



CLOSED REGIONS— NECESSITY AND APPLICATION. 



In addition to the provision of size limits it is strongly recom- 

 mended that certain jDortions of the rivers be closed for rest periods 

 covering several years. It might be thought that in regions of ex- 

 treme depletion the operation of a size limit would, by making the 

 fishery less profitable, have the effect of causing a practical rest pe- 

 riod, but this can not be expected, for, stimulated by the high price 

 of shells and the ever-present hope of making a pearl find, the local 

 shellers will hardly ever desist entirely from the fishery. 



No better way of giving protection to mussels can be found than 

 that of entirely stopping the shelling upon a series of beds, although 

 the plan must be applied in such a way as not to reduce the supply of 

 mussels unduly and suddenly and with as careful regard as possible 

 to the established interest of communities. 



INJURY TO SPAWNING MUSSELS AND TO YOUNG. 



Some of the conditions that make a system of closed regions par- 

 ticularly advisable for the conservation of fresh-water mussels may 

 be briefly mentioned: 



1. It has been previously stated that some of the mussels are spawn- 

 ing, or with spawn, during any period of the year. Many of the 

 most important species are spawning during the late spring, early 

 and mid summer; other equally important species form their eggs 

 in the late summer, when they become fertilized and develop into the 

 glochidium stage, but the mother clam retains them in marsupial 

 pouches within her shell during the entire winter and even into the 

 summer. All species of mussels carry the eggs in the marsupial 

 pouches during the process of development to the glochidium stage 



