Steller sea lions are less numerous than harbor seals but still widespread in the park, and in contrast to seals their numbers in Glacier Bay (but not elsewhere in southeastern Alaska) have risen steeply since the late 1980s. A non-breeding Steller sea lion haulout on South Marble Island has increased to over 500 sea lions in recent years, compared with fewer than 200 in the early 1990s. Researchers recently confirmed a new sea lion rookery with around 400 animals at Graves Rocks near Cape Spencer. The population of which they are a part is apparently thriving, unlike endangered populations in the western Gulf of Alaska and Bering Sea.
Sea otters were extirpated from the region during the 19th century and were reintroduced near the park in the 1960s. Their thriving populations have spread throughout the lower bay, and their numbers are now at over 8,000 in Glacier Bay. The burgeoning sea otter numbers drastically change the populations of their favorite prey such as mollusks, crabs and sea urchins, and consequently the structure of shallow-water ecosystems.
Black bears are widespread and common in forested areas, while the less numerous brown bear is most often found in open habitats and in proximity to salmon streams. Five species of terrestrial mustelids are present: short-tailed weasel, mink, marten, river otter and wolverine. Taken together, they occupy virtually all freshwater, terrestrial and marine shore habitats. Wolves appear to have increased in abundance since the establishment of moose in the park and preserve, and may be responsible for a corresponding decrease in coyotes. Red foxes patrol the outer coast beaches. A single cat, the lynx, is occasionally spotted around the Gustavus/Bartlett Cove area and occurs rarely in the Dry Bay area.
Among the ungulates, moose occur widely throughout thickets, meadows and open forests of lower elevations. The moose population in the Gustavus area has grown significantly in recent years. While Sitka black-tailed deer reach the northernmost portion of their natural range in the mature communities fringing Icy Strait, they are only occasionally spotted in Bartlett Cove and Gustavus forests. Mountain goats occupy massifs that offer the combination of precipitous escape terrain, good alpine meadows and sufficient high-altitude forests for winter shelter.