REPORT OF THE COMMISSIONER OF FISHERIES. 83 



Some of the females lay a batch of eggs before or while going south, 

 but probably the greater number lay no eggs until the following sea- 

 son. A certam small percentage of the young do not migrate up the 

 bay but remam to develop and mate in the lower waters. 



At the approach of cold weather the crabs settle to the bottom and 

 are usually supposed to bury there, but it is probable that they 

 simply he dormant and occasionally move slowly over the bottom. 

 Practically all females dredged during the winter, whether or not they 

 had spawned previously, were found to contain eggs and the live sperm 

 with wliich to fertilize them. There is no evident northward migra- 

 tion of such crabs m the spring. Most of the females die shortly 

 after the last batch of eggs is laid. Crabs mature in about a year, 

 growing in size by successive moltings. Mating occurs only at the 

 last molt of the female, when the abdomen changes from the tri- 

 angular to the apron form. The length of life is apparently two or 

 three years. 



An investigation of the spiny lobster, an important crustacean and 

 excellent article of food in the waters of southern Florida, was under- 

 taken about the middle of the fiscal year, and satisfactory progress 

 is being made. 



PROGRESS IN CULTURE OF DIAMOND-BACK TERRAPIN. 



The results of the continued experiments in diamond-back terrapin 

 culture at the Beaufort (N. C.) laboratory were given at some length 

 in the last annual report. The progress during the past year has 

 been gratifying, especially in the rapid growth of the yomig terrapin 

 hatched in the summer of 1916. The largest individual kept in a 

 warm house and fed during the winter was more than three inches 

 (80 mm.) in length of bottom shell. This is behaved to be a new 

 record for the growth of diamond-back terrapin in the first year of 

 life, and gives further encouragement to terrapin culture as a com- 

 mercial enterprise. 



STUDIES OF ANADROMOUS FISHES. 



At the beginning of the fiscal year, two particularly important 

 investigations were in progress relating to fishes which, though not 

 alike in structure or appearance, have the same intepesting and sig- 

 nificant habit of leaving the ocean and ascending streams for the pur- 

 pose of giving rise to a new generation. This habit is of particular 

 practical importance because essentially all the mature individuals 

 of the species are periodically assembled in definite runs in restricted 

 localities, when they are easy of capture on the one hand and available 

 for purposes of artificial propagation on the other. It is most de- 

 sirable that there should be available specific and reasonably complete 

 knowledge of the migrations of the shads and the salmons and of the 

 conditions to be met in protective measures and in practices of arti- 

 ficial propagation. 



Progress was made in the analyses of the data accumulated during 

 the field studies on the principal shad streams from St. Johns River, 

 Fla., to the St. Croix River, Me., and New Brunswick, but probably no 

 stage of completion can be reported until, with a change of conditions, 

 it becomes again possible to give the careful attention to the elaborate 

 measurements, comparisons, and analyses which the subject requires. 



