Population Dynamics and Inter-atoll Movement 
of the Hawaiian Monk Seal 
William 0. Wirtz, II 
« t 
ABSTRACT 
Monk seals were tagged and censused in the Leeward Hawaiians between 
February 1963 and July 1965, Most of the work was done at Kure Atoll, 
A total of 375 seals was tagged, 56 of them known age pups, and 1997 
subsequent sightings were recorded for the subadult and adult individ- 
* 
uals. Adult mortality is apparently low. Numbers of seals on the beach 
fluctuate irregularly. Only 10% of the total tagged seals were observed 
per census. Approximately 47% of the seals observed in a given month 
were not seen in the previous month. Limited inter-atoll movements of 
up to 300 miles are documented. The size of the population utilizing a 
given island at a given time may be from two to ten times the number 
counted on the beach. 
INTRODUCTION 
The Hawaiian monk seal, Monachus schauinslandi , is restricted in its 
distribution to six atolls In the Leeward Archipelago of the Hawaiian 
Islands. The total population is presently estimated at 1350 individuals 
(Rice, 1960). Because of the inaccessibility of its natural habitat 
relatively little has been published concerning the biology and ecology 
of this species. 
The Pacific Ocean Biological Survey Program of the Smithsonian 
Institution began tagging monk seals in early 1963 as one aspect of an 
ecological survey of the Leewards. Between September 1963 and August 
