250 
PACIFIC SCIENCE, VoL XIII, July 1959 
schauinslandi) is similar to the Weddell seal 
{Leptonychotes weddelli) in several aspects of 
behavior. The molt is epidermal, similar to 
that of elephant seals {Mirounga) . Monk seals 
more nearly resemble the Lobodontinae and 
Cystophorinae than the Phocinae. It is sug- 
gested that the Hawaiian monk seal may be 
only racially distinct from the Caribbean 
monk seal {M. tropicalis). 
2. The Hawaiian monk seal breeds only in 
the Leeward Chain of the Hawaiian Islands, 
on Kure Atoll, Midway Atoll, Pearl and 
Hermes Reef, Lisianski Island, Laysan Island, 
and French Frigate Shoals. They have occa- 
sionally been reported from Maro Reef and 
Nihoa Island. In the main Hawaiian Islands, 
they are rarely seen. Sightings are recorded 
from Hawaii, Oahu, Kauai, and Lehua. 
3. Monk seals appear to have few obvious 
adaptations to their tropical or subtropical 
environment. Like phocids of cooler regions, 
they are covered by a thick layer of blubber. 
A body temperature (35.5°C.), lower than 
temperatures recorded from seals inhabiting 
cooler climates, the black skin and black 
pelage of the pup may have significance in 
this respect. 
4. Habitat requirements include shallow 
waters (usually near coral reefs) for feeding, 
sandspits and beaches for hauling grounds, 
and permanent islets or beaches above high 
tide for pupping areas. 
5. Hawaiian monk seals were nearly ex- 
terminated during the nineteenth century, 
but have now successfully repopulated their 
former range. Aerial censuses and ground 
counts in 1956-57 placed the minimum pop- 
ulation at 1,013 in the summer of 1957. This 
included 94 pups, but the count of pups was 
incomplete at some atolls. Other uncounted 
seals were undoubtedly at sea. 
6. Sex was ascertained in a sample of 154 
animals including all age groups. Of these 
animals, 75 were males and 79 females. 
7. The annual reproductive rate (births per 
100 animals older than pups) is rather low: 
about 22 per cent at uninhabited Kure Atoll, 
and 8 per cent at Midway Atoll where the 
seals are subject to human disturbance. Field 
observations suggest that many adult fe- 
males miss pregnancy each year. 
8. Natural mortality among monk seals, 
both juvenile and adult, appears to be low. 
At Midway Atoll, six yearling seals were 
tagged and five pups were born in 1957, sug- 
gesting a high survival rate during the first 
year. A few monk seals carried large scars on 
their bodies; one apparently died of wounds 
inflicted by sharks. 
9. At Midway Atoll, results of tagging in- 
dicate that all of the seals range widely in the 
lagoon, and share a common home range. 
Seasonally, seals are most numerous on land 
during winter months. Daily, they are most 
numerous on land during the afternoon. 
10. While swimming, monk seals regularly 
use their front flippers, although their hind 
flippers and fishlike undulation of the body 
provide the chief means of propulsion. 
11. Two distinct vocal sounds are uttered: 
a deep-throated, soft, bubbling sound (often 
with mouth closed), and various bellowing 
sounds. 
12. Monk seals are genetically tame, but 
display threat behavior when closely ap- 
proached or annoyed, both on land and in 
the water. 
13. No marked social organization was ob- 
served. The seals are apparently sexually pro- 
miscuous. Courtship behavior was observed 
from early March to early July. 
14. The most important food items in the 
contents of two seal stomachs were conger 
eels {Ariosoma) and moray eels {Echidna and 
Gymnothorax)\ other items included flatfish 
(Bothus) and cephalopods (octopi.^). Appar- 
ently the monk seal is primarily a nocturnal 
bottom feeder, at least while frequenting 
atolls. 
15. The single young is born sometime be- 
tween late December or January and late June 
or early July, the majority during April and 
May. When newly born pups were observed, 
birth had taken place at night or early morn- 
