Abstract:
The Hawaiian monk seal is an endangered species with a current population of approximately
1400 animals. Seals are distributed primarily at six sites in the Northwest Hawaiian Islands. The
most depleted of these subpopulations occurs at Midway Atoll. Seal numbers declined at
Midway by over 90% from the 1950s to 1990s and currently stand at approximately 70 animals.
A cooperative agreement between the National Marine Fisheries Service and Hawaii Wildlife
Fund in 1997 led to the establishment of a year-round monk seal monitoring program at Midway
Atoll from 1997 – 2000. This project reports results from this year-round study.
Data for the study were based primarily on beach censuses that monitored monk seal haul outs at
Midway Atoll. Analyses examined (1) changes in haul out patterns by island over time, (2)
seasonal patterns in haul outs, (3) the influence of the barrier reef on monk seal beach counts, (4)
preferred pupping habitat, and (5) differences between year-round and seasonal data. Results
indicate that there was a shift in haul outs between islands over the course of the study. A strong
seasonal pattern in beach counts for immature animals was also identified. The barrier reef was
identified as an important haul out area, particularly for immature animals. Preferred pupping
sites were identified. Finally, year-round studies were shown to be valuable in the identification
of mother/pup pairs and in the development of female reproductive histories. Seasonal and yearround
studies performed equally well in determining average annual beach counts.
This study may prove important in identifying potential causes of the slow increase in the
Midway monk seal subpopulation. It may also suggest possible remedies or management actions
to promote or accelerate the recovery of monk seals at Midway Atoll. Recommendations for
future research are also discussed.
