Hawaiian Monk Seal — Kenyon and Rice 
223 
Fig. 2. Adult male monk seal, showing penile opening. When annoyed with a stick, a seal will usually roll on 
its side or back making definite recognition of sex possible. The distinct color difference along the side is not 
characteristic but is here the result primarily of the animal having rested on its belly. Midway Atoll, February 2, 
1957 (KWK 53-3-9). 
addition, 6 adults were tagged, 2 males, 3 
females, and 1 unidentified. 
On Green Island in Kure Atoll, we ob- 
served 11 adult males, 11 females with pups, 
15 additional females without pups, and 16 
adults of unknown sex. The observed sex 
ratio was strongly biased, of course, because 
of the large unsexed element and because 
animals with pups were obviously females. 
On the sandspits west of Green Island, 
Comdr. J. F. Reilly counted 8 females and 10 
males. The total for Kure was 21 males and 
34 females. 
Among 154 seals of all age classes, in which 
sex was determined, were 75 males and 79 
females. 
Sex ratio data on adult and subadult seals 
must be interpreted with caution because of 
the possibility of differences in hauling-out 
habits of the two sexes. 
Age at Sexual Maturity 
Monk seal pups and presumed yearlings 
were first marked with metal tags in 1957. 
Therefore, no positive data on growth rates 
and age at which reproduction takes place 
will be available for several years. According 
to Bertram (1940), the Weddell seal normally 
bears her first pup late in her third year and 
some crabeater seals {Lohodon carcinophagus) 
give birth at the age of 2 years. According to 
Laws (1956^), the southern elephant seal usu- 
