PROGRESS IN BIOLOGICAL INQUIRIES. 1937 g^ 



with concentrations of 521, 482, and 310 adults per pound, respec- 

 tively. 



The best results were obtained when 310 adult terrapins were con- 

 fined in a pen 60 feet square, at a ratio of 1 male to (> females. This 

 lot produced a total of 2,511 young. Two recent collections of wild 

 stock, aggregating 342 invididuals, show that when tlie terrapin con- 

 gregate at the natural breeding areas there is a sex ratio of approxi- 

 mately 1 to 6. Of further interest in this connection is the fact that 

 terrapin previously reared from the egg to sexual maturity at the 

 Beaufort station show a ratio of 1 male to 6.4 females. 



Studies were also made in the early summer to determine whether 

 a portion of the brood stock, consisting of rather old females, wer^ 

 "boarders" and incapable of eg^ production. Examination of several 

 marked specimens from the original brood stock which has been in 

 captivity since 1909, showed that each contained from 7 to 9 com- 

 pletely formed eggs and approximately 3 times this number of de- 

 veloping ova of various sizes. The mature eggs taken from these 

 animals were placed in the sand beds used for incubation and showed 

 a hatch of over 85 percent. Tliese observations indicate that dia- 

 mond-back terrapins are capable of producing a good supply of 

 eggs and young until they are at least 40 years of age. 



UtUhation of marsh areas for oi/ster and mullet propagation. — In 

 many parts of the world improved marsh areas and tidal flats ar-^ 

 successfully used for fish and shellfish propagation. In cooperation 

 with the Works Progress Administration a project was undertaken 

 to construct a series of marsh ponds in the vicinity of the Beaufort 

 laboratory to determine the value of such structures for increasing 

 the production of oysters, mullet, and possibly other marine animals 

 in the South Atlantic and Gulf i-egion. 



The construction of one large tidal pond. 2i/2 acres in extent, and 

 several smaller ponds, 20 by 40 feet, is virtually completed and will 

 be ready for experiments in 1938. A substantial dike 800 feet long 

 separates the large pond from adjacent waters but permits a regular 

 exchange of sea water by means of two tide gates. Each gate is 

 supplied with 9 wire screens of 3 different mesh sizes to retain the 

 young mullet that are to be placed in the pond in the early summer. 

 The general plan is to rear the mullet to marketable size in this ex- 

 perimental pond from which they may be harvested at any time of 

 the year, and to determine from its operation the most satisfactory 

 and practical procedure for producing these fish in commercial 

 quantities in larger ponds or controlled tidal bays. A considerable 

 area of hard bottom, created in the pond by deepening and leveling 

 operations, is suitable for giowing oysters and clams and will be 

 stocked with these shellfish. The shells of the oysters generally sup- 

 port a good growth of plant life which serves as a natural food 

 supply for the mullet. 



The series of smaller ponds which will be used primarily for oyster 

 culture experiments haA^e been excavated in a representative salt 

 marsh area Avith adjustable gates for controlling the depth and flow 

 of water. Ordinarily if seed oysters were planted at ])ond level so 

 as to be exposed to air at times of low water they would produce in- 

 ferior market stock because of attachment and crowding of subse- 

 quent generations. However, by maintaining a minimum depth of 



