Characterization of Hawaiian Monk Seal....
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GRANT NUMBER:                       NMFS NUMBER:   97-SW-03

REPORT TITLE:  Characterization of Hawaiian Monk Seal (Monachus schauinslandi) Pelagic Habitat, Home Range, and Diving Behavior

AUTHOR:  Brent S. Stewart, Mitchell P. Craig, and George A. Antonelis

PUBLISH DATE:  April 1, 1998

AVAILABLE FROM:  George A. Antonelis, National Marine Fisheries Service, Southwest Fisheries Science Center Honolulu Laboratory, 2570 Dole Street, Honolulu, Hawaii 96822-2902.  TELEPHONE:  (808) 983-5710


Hawaiian monk seals (Monachus schauinslandi) have declined at their six principal colonies in the Hawaiian archipelago by about 60% since the late 1950s and now number around 1,300-1,400.  The obstacles to species recovery are unclear, although decline or depletion of important prey resources has been posited as a key factor.   Identificaiton of foraging habitats is fundamental to clarifying that relationship and formulating appropriate management measures that may promote the seals' recovery.   The objectives of this study were to (1) document geographic and vertical foraging habitats used by monk seals at an increasing colony (Pearl and Hermes Reef), (2) compare those patterns with comparable data at a declining colony (French Frigate Shoals), and (3) evaluate the hypothesis that prey availability is limiting the French Frigate Shoals population.  The investigators documented geographic and vertical components of the foraging patterns of nine adult male, nine adult female, and six juvenile (five male and one female) Hawaiian monk seals at Pearl and Hermes Reef from November 1997 through September 1998 using satellite-linked telemetry.  Seals at Pearl and Hermes Reef foraged mostly in relatively shallow (8-40 m) waters within or on the outer slope of the atoll, rarely ranging more than a few kilometers away.  Moreover, seals segregated by age and sex when foraging within this small atoll.  In contrast, earlier studies reported that seals at French Frigate Shoals foraged deeper and further away (up to 217 km from haulout sites) and did not generally segregate.  These data support the hypothesis that prey resources may be more dispersed and perhaps less abundant at French Frigate Shoals.  The data also highlight the importance of, and critical need for, spatial and temporal details of the foraging patterns of Hawaiian monk seals, particularly of young seals, at various colonies for strategic conservation and management.

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