Current address: National Marine Fisheries Service, 2570 Dole Street, Honolulu, Hawaii 96822, U. S. A.
BODY SIZE, SURVIVAL, AND DECLINE OF JUVENILE HAWAIIAN MONK SEALS, MONACHUS SCHAUINSLANDI
Article first published online: 26 AUG 2006
Marine Mammal Science
Volume 15, Issue 3, pages 786–809, July 1999
How to Cite
Craig, M. P. and Ragen, T. J. (1999), BODY SIZE, SURVIVAL, AND DECLINE OF JUVENILE HAWAIIAN MONK SEALS, MONACHUS SCHAUINSLANDI. Marine Mammal Science, 15: 786–809. doi: 10.1111/j.1748-7692.1999.tb00843.x
Current address: National Marine Fisheries Service, P. O. Box 21668, Juneau, Alaska 99802, U. S. A.
- Issue published online: 26 AUG 2006
- Article first published online: 26 AUG 2006
- Received: 14 November 1997 Accepted: 28 October 1998
- Hawaiian monk seal;
- Monachus schauinslandi;
- conservation biology
In the mid 1980s half of the entire Hawaiian monk seal species was located at French Frigate Shoals, and this colony may have reached environmental carrying capacity. Since 1989 this colony has declined by 55%, primarily from poor juvenile survival. Only 8%–25% of weaned pups have survived to age 2 during this period, compared to at least 80% between 1984 and 1987. We characterize (1) this drop in survival, (2) a strong, but variable, correlation between survival and size at weaning, (3) interisland differences in size from weaning to age 2 in 1991 through 1993, and (4) decadal-scale changes in mean measures of size at weaning. We compare observations at French Frigate Shoals with the colony at Laysan Island where abundance is well below historical levels and was therefore expected to be below carrying capacity. At Laysan Island juvenile survival has also been poor (30%-70%), and the size of weaned pups has decreased during the past decade. Our hypothesis is that poor survival may be due to reduced prey availability at both sites, but particularly at French Frigate Shoals. Evidence to support this hypothesis includes a large increase in total abundance at French Frigate Shoals; reduced size of weaned pups; decreased survival, emaciation, and slower growth rates of juvenile seals; and declining primary productivity. Regardless of cause, the immediate consequences at French Frigate Shoals and Laysan Island, and for the species overall, will likely be poor recruitment and productivity. Because the decline is still in progress, the ultimate consequences for the species' viability are of great concern in light of its already low abundance.