Hawaiian Monk Seal — Kenyon and Rice 
TABLE 3 
Mean Air and Surface Water Temperatures 
(°F.) AT Midway Atoll 
MONTH 
AIR^ 
SURFACE 
WATERS 
Mean 
high 
Mean 
low 
Mean 
January 
70 
62 
66 
68.4 
February. 
69 
62 
66 
66.8 
March 
70 
63 
66 
66.4 
April 
72 
64 
68 
66.9 
May. . 
75 
68 
72 
69.5 
June 
80 
72 
76 
73.6 
July. 
82 
74 
78 
76.4 
August 
82 
75 
78 
77.5 
September. 
82 
75 
78 
78.1 
October. 
79 
73 
76 
75.8 
November . 
76 
69 
73 
73.2 
December 
73 
66 
69 
69.7 
ANNUAL MEAN. . . . 
76 
69 
72 
71.8 
1 Data from Aerology Unit, U. S. Naval Station, Midway 
Island, 1941—57. Highest on record, 92 °F.; lowest, 54°F. 
2 Data from Atlas of Climatic Charts of the Oceans, U. S. 
Weather Bureau, 1938, for the quadrat 175°— 180° W., 25°— 
30°N. 
hairs being only about 2-9 mm. long. The 
pelage of adult phocids can have little effect 
as a temperature regulator. However, in the 
young of cold-water seals which have not yet 
developed a blubber layer, the wooly natal 
pelage undoubtedly functions as an insulator. 
At birth, monk seals have a single-layered 
black pelage consisting of straight silky hairs 
6-10 mm. long. In this respect, they differ 
markedly from the young of arctic phocine 
seals and antarctic lobodontine seals, which 
possess a wooly coat about 15-25 mm. long. 
Pups of the southern elephant seal have a 
single-layered wooly pelage about 23 mm. 
long (Laws, 1954). The lack of pelage with 
marked insulating properties in young monk 
seals may be a climatic adaptation. In this 
connection, it is interesting to note that, in 
young harbor seals, the white wooly fur is 
retained for several weeks after birth in the 
northern Bering Sea but is lost in a prenatal 
molt in southern parts of the species’ range 
(Scheffer and Siipp, 1944). 
In addition to black pelage, the newborn 
monk seal has nearly black skin. It has been 
suggested that black pigment is a protective 
219 
shield against harmful insolation. Prior to 
weaning, the monk seal pup spends much 
time in intense sunlight on the white coral 
sand beaches. 
Habitat Requirements 
Certain features are characteristic of monk 
seal breeding sites, as follows. 
FEEDING AREAS: Seals occur regularly only 
on islands and atolls having extensive areas 
of shoal water. At Midway and elsewhere, we 
frequently saw seals swimming inside the reef 
but did not see them outside the lagoon, in 
deep water. That they do range in deep water, 
however, is evidenced by records far from the 
breeding grounds and by the fact that remote 
islands, such as Laysan, have been repopu- 
lated after local extermination took place dur- 
ing the 19th and early 20th centuries. Another 
indication that monk seals may spend con- 
siderable time at sea is the observation that 
certain individuals, when we saw them for the 
first time, exhibited a heavy growth of green 
algae in the hair on various parts of the body. 
The green tinge was lost after a number of 
days spent on Midway beaches. Food analysis 
indicates that they feed primarily on bottom 
fishes, kinds which they could obtain only in 
comparatively shallow water. In the lagoons, 
a rich bottom fauna is found on coral reefs 
and bordering sand areas, 
HAULING GROUNDS: Monk seals generally 
haul out on sandy beaches and sandspits. 
They are absent from high rocky islets, which 
lack beaches, in the eastern half of the Lee- 
ward Chain. Though they prefer sand to 
rocks, they are occasionally seen on low, 
shelving reef rocks which slope into the water 
on Eastern Island and on reef rocks surround- 
ing atoll lagoons. The southwest side of 
Laysan Island is bordered by a fairly high 
ledge of coral rock; we have never seen a seal 
hauled out along this stretch of shore, al- 
though they haul out on the low beaches 
bordering it. The shade of Scaevola frutescens, 
above the beachline is attractive to seals. 
