ILIAMNA LAKE SEAL } A distinct population segment (DPS) of Phoca vitulina richardsi
Family: Phocidae

DESCRIPTION: Locals of the Lake Iliamna region describe the seals as bigger, darker, fatter, with a unique fur pattern and oilier coat than saltwater seals. Because Iliamna Lake seals are described as larger than saltwater seals, they likely fall at the higher end of the ranges for body weight and length for harbor seals in Alaska. In Alaska, adult male harbor seals range from 160 cm to 186 cm and 87 kg to 170 kg, while adult females range from 148 cm to 169 cm and 65 kg to 142 kg

HABITAT AND RANGE: Iliamna Lake seals are the only harbor seals in the U.S. that live exclusively in freshwater habitat. They haul-out on the low-lying parts of islands and lakeshore in the northeastern half of Lake Iliamna, and hunt for fish in the waters of the lake.

MOVEMENTS: Harbor seals are not a migratory species, and the DPS of harbor seals in Iliamna Lake stay in the lake throughout their lives. Documented ranges of the only other freshwater population of harbor seals, located in Canada are from 83 to 891 square km, with the longest straight-line distance of 30 km. If Iliamna Lake seals have a similar home range size, they remain in only in the northeastern half of the lake.

REPRODUCTION: If the Iliamna Lake seal population is similar to its marine counterparts, then the average age at first reproduction is about three to four years for females and four to five years for males. Iliamna Lake seals give birth to pups in July, which coincides with peak sockeye salmon runs in the lake, giving nursing mothers an energetically rich food source. Iliamna Lake seals give birth to pups approximately one month later than the closest population of saltwater harbor seals in Bristol Bay. Based on aerial surveys, Iliamna Lake seals appear to haul in small herds during the breeding season. Iliamna Lake seal pups appear to be precocial and swim quickly after birth. Pacific harbor seals nurse pups for about four weeks to six weeks, after which the pups are rather abruptly weaned, and subsequently left to fend for themselves.

FEEDING: The resident Iliamna Lake seal population is supported by massive annual salmonid runs, and by abundant lake fish species. Other species consumed by Iliamna Lake seals include resident lake trout and Arctic char, as well as species that often migrate from the rivers to the lake, such as rainbow trout and Dolly Varden. Iliamna Lake seals also eat juvenile salmonids, as well as lamprey and smelt, and the occasional whitefish, sculpin and stickleback. Resident lake fish species, and juvenile salmon likely comprise the majority of the Iliamna Lake seal’s diet when adult salmonids are absent.

THREATS: The persistence of the Iliamna Lake seal is tightly linked to the abundant summer and fall salmon runs and presence of juvenile salmon in the lake year round. The salmon face severe threats from climate change and ocean acidification and from Pebble Project development. The seals are also directly threatened by disturbance from increased human activity, including plane, boat and motor vehicle traffic that would result from Pebble Project. Pebble Project would also degrade both terrestrial and aquatic habitat used by the seals. Changes in ice extent, water level, and precipitation patterns from climate change may also alter winter-use habitat for the seals.

POPULATION TREND: A lack of reliable data makes estimating the seals’ population trends difficult. The total population of seals in the lake is estimated at between 250 and 350 adults.

Iliamna Lake seal photo by Dave Withrow, NOAA