Hundreds of harbor seals rest on ice bergs in an ice-filled bay in Southeast Alaska. This is Johns Hopkins Inlet in Glacier Bay. Johns Hopkins glacier is actively calving into the water, and the icebergs are extremely important habitat for pupping and nursing harbor seals in Alaska. Harbor seals in Glacier Bay mate during July and August and have their pups in May and June. Pups are about 25 pounds when they are born, and grow quickly on fat-rich milk, doubling their birth weight in the three to six weeks before they are weaned.
Johns Hopkins Inlet is the site of one of Alaska's largest breeding colonies of harbor seals. In 1992, more than 4,000 harbor seals were counted in the Inlet. But that's changed, and today there are far fewer seals here than there used to be.
In August 1992, 6,370 seals were counted in a survey of Glacier Bay, and most of the seals were in the ice-filled waters of Johns Hopkins Inlet. In 2001, just 2,650 seals were counted in Glacier Bay, and there were 60% fewer seals were in Johns Hopkins. Rates of decline in harbor seal numbers in Glacier Bay are comparable to those observed in the Gulf of Alaska, where an area-wide decline in harbor seals, Steller sea lions and fish-eating seabirds has been documented.
Causes of decline could be increased mortality, reduced birth rates, or emigration from Glacier Bay to other areas. Increased predation by sleeper sharks and Steller sea lions, and shifts in diet are hypothesized causes of the declines, and researchers are testing or plan to test these hypothesis in the near future. In addition to monitoring the distribution and abundance of seals in the Bay, researchers are also studying seal diet, genetics, and behavior, including responses to vessel traffic.