246 
TABLE 10 
Weights and Lengths of Living 
Hawaiian Monk Seals 
DATE, 
SEX 
AGE 
weight 
length^ 
1957 
(lbs.) 
(cm.) 
April 2 
cT' 
1 day 
36 
■ 97.5 
April 2 
c7 
1 day 
38 
95.0 
March 27 ... . 
c7 
4 days 
44 
102.5 
March 27 ... . 
c7 
4 days 
46 
100.0 
Mean for newly born pups . . . 
41 
98.75 
January 14. . . . 
c7 
yearling 
112 
128.0 
March 5 
9 
yearling 
69 
114.0 
March 5 
c7 
yearling 
102 
129.0 
March 5 
9 
yearling 
92 
130.0 
March 5 
9 
yearling 
111 
145.0 
March 5 
c7 
yearling 
108 
136.0 
Mean for yearlings 
99 
130.3 
^ Straight line, tip of nose to tip of tail, animals lying on 
their bellies. 
probably may be attributed to an error in 
reading the scales.) Considerable observation 
will be necessary to ascertain when the pup 
begins to maintain itself by feeding. 
The mean weight of six yearlings was 99 
pounds, and their mean leiigth 130.3 cm. 
(Table 10). It is interesting to note that the 
length of yearlings increases little over that 
of the newly weaned pup and that newly 
weaned pups usually weigh considerably more 
than yearlings. Similar conditions have been 
shown in other pinnipeds (Scheffer and Wilke, 
1953). This indicates that the adjustment 
from nursing to an independent existence, 
when the animal must obtain its own food, 
is strenuous. The substantial store of blubber 
is undoubtedly a valuable store of nourish- 
ment during early attempts to find food. 
SUBADULTS AND ADULTS: A young seal, 
judged to be a yearling, weighed 119 pounds 
on July 21, 1957, shortly after capture. On 
September 2, 1957, it weighed 134 pounds 
and on February 5, 1958, 200 ^ 25 pounds, 
estimated (G. H. Pournelle, m lit.). If a curve 
is projected on the basis of these weights, it 
appears possible that the monk seal may ap- 
PACIFIC SCIENCE, Vol. XIII, July 1959 
proach adult size in its third year. A rapid 
growth rate might be expected, since related 
forms, the Weddell and crabeater seals, are 
believed to attain adult size in 1 year (Ber- 
tram, 1940). 
On February 2, 1957, four adult male monk 
seals were examined as they lay sleeping on a 
small islet at Midway. All were about the 
same size. The one estimated to be slightly 
largest was shot (now BDM 490). It was cut 
up and weighed in sections on a 100-pound 
capacity spring scale. Measurements and 
weights are recorded below. 
Measurements: 
Total length^ 2,142 mm. 
(7 ft. Vk in.) 
Front flippers^ 369 mm. 
Hind flippers^ 342 mm. 
Tail 170 mm. 
(approx.) 
Rectum to penile opening. . . 380 mm. 
Girth behind flippers 1,300 mm, 
Large intestine, length 1,410 mm. 
Small intestine, length 2,200 cm. 
(64 ft. 8 in.) 
Thickness of blubber, 
mid-belly region: 
outer layer 27-29 mm. 
inner layer 15-16 mm. 
Total 42-45 mm. 
Weights (pounds): 
Stomach and contents 8.5 
Liver and gall bladder 11.5 
Intestines 19.5 
Kidneys 2.5 
Heart 1.6 
Remainder of carcass 336.4 
Total 380.0 
^ Tip of nose to tip of tail, animal lying on its back. 
2 Flippers held at right angle to body, measured 
along anterior margin. 
No adult females were collected. The length 
of a large living female measured as it lay flat 
on its belly on a smooth sand beach, was 
7 feet 8 inches; her weight was estimated at 
600 pounds. Fully adult females, in general, 
appeared larger than males. Pregnant and 
newly postpartum females are far more obese 
than any male seen. One large female was 
estimated to weigh about 575 pounds im- 
mediately after the birth of her pup. This 
