34 
BULLETIN OF THE BUREAU OF FISHERIES 
been due to a difference in fecundity rather than to the number of mature females 
present. 
The highest degree of fertility for all broods on hand or used at one time or another 
in the many experiments conducted has almost consistently occurred among wild 
terrapins (Table 8) that have been confined for breeding purposes. The product of 
all wild animals is considered together here for convenience, although these terrapins 
have been separated into smaller lots at various times. To give a record of each lot 
separately would require much space. When last enumerated (1926) there were on 
hand 39 males and 72 females belonging to this “wild stock,” and this ratio has not 
varied greatly for several years. Fertility among the wild terrapins, or the “orignal 
brood stock,” during the period 1912 to 1926 was lowest in 1912, which was the first 
year of confinement for the majority of these animals, when 83.9 per cent of the eggs 
hatched. Two years later (1914) it was the highest that it has ever been, namely, 
97.9 per cent. The average fertility for the entire period was 94.4 per cent. 
In the case of a few groups of animals the results with respect to fertility, as 
related to sex ratio, are contrary to the more general rule stated in a preceding 
paragraph, namely, that a large proportionate number of males tends to bring about 
a high percentage of fertile eggs. The 1910 brood (Table 10), for example, was 
divided into two lots. One lot was fed the first winter, the other being allowed to 
hibernate. The first-mentioned lot has one male to nine females and an average 
percentage of fertility for the entire period during which eggs have been produced 
(1915 to 1926) of 85.2 per cent; whereas in the hibernating lot, in which there is a 
ratio of one male to 7.8 females, the percentage of fertility during the period (1916 
to 1926) in which eggs have been produced is only 71.8 per cent. 
It is evident from the foregoing discussion that the reason or reasons for the 
great fluctuations in fertility among the various lots and broods and even within 
a single lot and brood are not understood, and that sufficient data are not yet at 
hand from which specific recommendations relative to the proper sex ratio that 
should be maintained for breeding purposes may be made. This question is further 
complicated by the fact that females appear to produce a high percentage of fertile 
eggs for at least two years without recopulation. Thereafter, fertility apparently 
drops rapidly. This conclusion is based upon the results obtained from penning 10 
old females without males. During the first season following separation from males 
these 10 females laid 124 eggs, and only 1 failed to hatch; during the second summer 
116 eggs were produced and 14 failed to hatch; during the third summer 130 eggs 
were laid and 91 failed to hatch; and during the fourth summer 108 eggs were pro- 
duced and only 4 hatched. Thereupon, seven old males were introduced, and in the 
next season 145 eggs were laid, of which only 4 failed to hatch. The results of this 
experiment would indicate that annual copulations are not necessary, and that very 
few males would suffice for breeding purposes. The combined records for all adult 
terrapins on hand appear to show, however, that the highest rate of fertility is 
obtained when the males are fairly numerous. The indications are that for breeding 
purposes a ratio of about 1 male to 5 females should be maintained. 
