Northern fur Seals on Pribilof Islands of Alaska
Roughly 50% of the world’s northern fur seals breed in the eastern Bering Sea on the
Pribilof Islands of Alaska. The species has a rich history of exploitation for its
luxurious fur and while various subpopulations have experienced periods of stability
and recovery from sealing activities, today the overall population is declining. Many
explanations for population decline have been proposed: predation, conflict with commercial
fisheries, reduced prey abundance/quality, and warming seas. My research focuses on
establishing a tool for wildlife managers that is both accurate and cost effective.
To do this I tagged adult female northern fur seals with radio transmitter tags that
are capable of telling me how long mother seals spend foraging at sea as well as how
long they spend on shore nursing their pup. The longer mom spends foraging at sea,
the longer her pup is left alone onshore fasting without food, inevitably losing weight
if left alone for too long. Previous studies have linked pup weight to survival, noting
that pups who wean heavier have a greater chance of surviving their first winter without
mom. I suspect that when prey is hard to find, or other conditions are unfavorable
like warm ocean temperatures, mother’s spend extra time searching for food. In conjunction
with foraging trip duration measurements, we weigh the pups and have shown that indeed,
when mom spends extended times foraging, her pups lose weight. Because we know survival
increases with weight, in years when mom’s spend extra time foraging, we may expect
survival to decline. This relationship suggests that maternal foraging trip durations
can be used as an inexpensive tool of evaluating reproductive success in a depleted
marine mammal species.
Greg Merrill (UAA) applies a radio transmitter to the flipper of an adult female northern
fur seal on St. George Islands, AK, to track the animal’s time foraging at sea. NMFS
Permit #14327-01. Greg Merrill (UAA) waits to tag a female northern fur seal on St. George island as
John Edwards (NOAA Alaska Ecosystems Program) and Greg Balogh (NOAA Alaska Regional
Office) safely restrain the animal in a neoprene vest. NMFS Permit #14327-01. Photo
credit: Rebekah Leverty.
An Arctic fox observes the tagging crew weighing an adult female on a northern fur
seal breading colony. Look closely at the boulders in the background. A lot of them
are seals! NMFS Permit #14327-01.
Harnessed to a cliff edge, Greg Merrill (UAA) uses a spotting scope to identify tagged
northern fur seals hauled out on the breeding rookery below. An adult female northern fur seal cautiously spies on the activities of the tagging
team. NMFS Permit #14327-01. Photo Credit: Greg Merrill
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