Home Range Analysis of Hawaiian Monk Seals (Monachus schauinslandi) Based on Colony, Age, and Sex

Abstract: Low survival rates of juveniles in populations of the endangered Hawaiian monk seal (Monachus schauinslandi) in the Northwestern Hawaiian Islands are believed to be the leading cause of the species’ decline. One hypothesis is that younger seals are starving due to poor foraging success. Because high mortality of young seals poses a significant risk to population-level survival, increased knowledge of the specifics of weaned pup and juvenile foraging is of paramount importance. We used telemetry data and the most recent movement modeling techniques to compare monk seals’ home ranges across various age and sex groups among five of the six primary breeding colonies in the Hawaiian Islands. We found significant differences in size and spatial patterns of home ranges at the regional and colony level, following a decreasing productivity gradient from the northwest to the southeast. Home range size was significantly smaller in the three northwestern colonies than the two central-northeastern colonies. Adult seals in one colony at the lower end of the productivity gradient had smaller home ranges than younger seals, perhaps indicating that lower levels of prey abundance are forcing younger seals to forage further away from the colony where larger adult seals outcompete them. Uniqueness in seal movement on Pearl & Hermes Reef might be associated with increased southerly latitudinal movement of the Transition Zone Chlorophyll Front, which brings nutrient rich waters and a potential surge in productivity, supporting the theory that better prey availability reduces home range size. The wide variability in home range sizes and locations suggests that a universal approach to managing monk seals on different colonies would be unsuccessful. Results here suggest that animals from different colonies may perceive habitat differently; these differences should be taken into account when translocating animals to new habitat.

Key Words: Hawaiian monk seal, Monachus schauinslandi, home range, space use, utilization distribution, kernel density estimates

Document Type: Research article

DOI: 10.1578/AM.37.3.2011.360

Page Numbers: 360-371

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