NMFS NUMBER: 95-SWR-068
of Hawaiian Monk Seal, Monachus schauinslandi,
Pelagic Habitat Use: Range and Diving Behavior
Abernathy, Donald B. Siniff, Ph.D.
National Marine Fisheries Service, Southwest Region, 501
West Ocean Boulevard, Room 4200, Long Beach, CA 90802-4213.
TELEPHONE: (562) 980-4033
the apparently food related decline in the population
of Hawaiian monk seals at French Frigate Shoals in the
Northwestern Hawaiian Islands has been hampered by an
almost complete lack of information about monk seal foraging
ecology. This study investigated movement and diving behavior
of adult seals at FFS using satellite-linked, time-depth
recorders. Many seals of both sexes that left the atoll
spent time at various shallow banks 30 - 200 km away.
Males and females traveled to equally distant banks, but
there was some indication that a lower percentage of females
depart the atoll. There was a slight, but inconclusive
difference in distance traveled by adult and subadult
seals. Comparison of dive depth and duration histogram
data indicated a lower proportion of dives below 80m by
females. Distinct modes of diving activity were seen in
the 40-80m, 110-180m, and >300 ranges. There were day
versus night shifts in diving activity that likely correspond
to prey availability. There appeared to be three rough
classifications of movement and diving behavior: (1) Mid-range
divers that frequented the banks, (2) Shallow divers that
remained in the vicinity of FFS, and (3) Deep divers that
were active along a ridge to the east of the atoll. Hawaiian
monk seals at French Frigate Shoals frequently exceed
the current critical habitat boundaries.