The Northern fur seals that breed
on the Pribilof islands have been on the
decline for decades, a smaller colony just 200 miles away is thriving. As
KUCB’s Lauren Rosenthal reports, a new study of these colonies is challenging
scientists’ assumptions about what marine animals need from their environment
-- and how they get it.
The National Marine Mammal
Laboratory sends a team to the Pribilofs every two years to count new Northern
fur seal pups. Since 1998, the overall production of pups has dropped by 45%,
but according to the latest count, the Pribilof fur seals bucked the downward
trend for the first time in 15 years.
Rod Towell, a statistician
from the mammal lab, says pup production increased a tiny amount in 2012 – just
0.5%. While it’s not statistically significant, Towell says that the data is
[[24 fur seal – 1, 4s, “decline again”In
my estimation, it’s a good sign in the sense that it didn’t decline again.]]
Meanwhile, on Bogoslof Island, it’s a different story. Pup
populations have increased every year since the first pup was spotted there in
1980. A group of researchers has been studying why this island’s on the rise,
while the Pribilofs are in decline.
Andrew Trites is a fisheries
professor at the University
of British Columbia.
Trites was on the team to study the animals’ diets for clues.
[ 24 fur seals - 2, 12s, “to
decline”<<It was to really understand how top predators, [like] seabirds,
and fur seals interact with the environment. How do they find their prey? What
drives their numbers to increase? What causes them to decline?>>]]
One of the biggest issues is how
they eat. The Northern fur seals, black-legged kittiwakes and thick-billed
murres that the group studied all have to make tradeoffs between the energy
they spend to reach their prey, and the energy they get from that food source.
Until recently, scientists
weren’t sure how the animals judged that tradeoff. Contrary to what they
expected, Trites and his fellow researchers found that the seabirds and fur
seals don’t go to areas with the highest biomass of prey, or even the highest
number of prey. That information is what fish management decisions are based
But the fur seals and seabirds
don’t behave like resource managers. Instead, they behave more like fishermen.
Just like trawlers searching for schools of fish, the fur seals and birds go to
patches – areas where there’s a dense school of fish or krill – and eat
Those patches change often,
depending on a slew of conditions that affect the prey’s behavior, and the
researchers don’t yet understand why the animals use them.
In a presentation at the
Marine Science Symposium in Anchorage,
Trites went over his piece of the research, which compared Pribilof foragers to
[ 24 fur seal – 3, 21 s, “in
diet”<<Primarily, the murres and the fur seals in the Pribilofs where
they’re declining -- they really eat a lot of pollock. And we discovered
down at Bogoslof, they’re not eating pollock. They’re eating mostly squid and
Northern smoothtongue, or these deepwater fishes that are high in energy. So a
big difference in diet.>>]
Trites thinks that the
Pribilof seals are declining because they’re eating juvenile pollock, which he
says don’t have enough energy. He says the group’s research shows that in order
for the seabirds and fur seals to recover, the ecosystem around the islands
would have to shift.
[24 fur seal – 4, 13s, “to the
pribilofs”<<You can see that under the right feeding conditions, if
you’ve got high-energy prey near these islands, they can rebound. And hopefully
we’ll see that return one day too to the Pribilofs.>>]
The results of the Bering Sea study were published in January in the journal
PLOS ONE [ploss one].
In Unalaska, I’m LR.