Body size, survival, and decline of juvenile Hawaiian monk seals, Monachusschauinslandi

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 ca rrying 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 char acterize (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 i n mean measures of size at weaning. We. compare observations at French Frig ate Shoals with the colony at Laysan Island where abundance is well below h istorical levels and was therefore expected to be below carrying capacity. At Laysan Island juvenile survival has also been poor (30%-70%), and the si ze Of weaned pups has decreased during the past decade; Our hypothesis is t hat poor survival may be due to reduced prey availability at both sites, bu t particularly at French Frigate Shoals. Evidence to support this hypothesi s includes a large increase in total abundance at French Frigate Shoals; re duced size of weaned pups; decreased survival, emaciation, and slower growt h rates of juvenile seals; and declining primary productivity. Regardless o f cause, the immediate consequences at French Frigate Shoals and Laysan Isl and, and for the species overall, will likely be poor recruitment and produ ctivity. Because the decline is still in progress, the ultimate consequence s for the species' viability are of great concern in light of its already l ow abundance.