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Zoo sup­ports research of polar bears’ shift­ing diets by cli­mate change

pub­lished 27 April 2016 | mod­i­fied 27 April 2016

Polar bear Tasul Oregon zooYou really are what you eat. That’s the taking-​off point for a new polar bear study, con­ducted by U.S. Geo­log­i­cal Sur­vey (USGS) researchers with an assist from the Ore­gon Zoo — and pub­lished online on 18 April in the jour­nal Phys­i­o­log­i­cal and Bio­chem­i­cal Zool­ogy.

As sea ice shifts in the Arc­tic, sci­en­tists have noted a cor­re­spond­ing shift in polar bears’ diets. In West­ern Hud­son Bay, for exam­ple, sea-​ice loss has been asso­ci­ated with declines in the con­sump­tion of benthic-​feeding prey, such as bearded seals. In East Green­land, polar bears have increased con­sump­tion of hooded seals and decreased con­sump­tion of their more typ­i­cal prey, ringed seals.

The degree to which these types of changes are com­mon through­out polar bear pop­u­la­tions, and their impli­ca­tions on bear health, are not well under­stood. To deter­mine whether bears are chang­ing their diet in these remote Arc­tic regions, sci­en­tists are gath­er­ing base­line data from a cou­ple of ani­mals closer to home — Tasul and Con­rad, two res­i­dent polar bears at the Ore­gon Zoo.

Sci­ence can some­times be a slow process,” said Amy Cut­ting, who over­sees the zoo’s North Amer­ica and marine life areas. “And cli­mate change is hap­pen­ing rapidly. Any­thing we can do to quickly gain infor­ma­tion about how polar bears respond will help man­agers make crit­i­cal deci­sions for pro­tect­ing them in the wild.”

Sta­ble iso­topes
Using a handy chem­i­cal tool called “sta­ble iso­topes” — which include the car­bon and nitro­gen atoms that exist in every liv­ing thing — researchers from the USGS are reveal­ing how polar bears, which cur­rently boast the highest-​fat diets of all the ani­mal king­dom, process dif­fer­ent types of meals.

This new tool is allow­ing us to use hair and blood sam­ples to dis­cover whether polar bear diets have changed since the ‘80s, when we began keep­ing records
Dr. Karyn Rode, research leader, USGS wildlife biologist »

This is pos­si­ble, Rode says, because when a polar bear eats a meal of seal, whale or wal­rus, it takes on that organism’s iso­tope load as well. These chem­i­cal mark­ers can then be detected in the bears’ own tis­sue sam­ples, such as their blood or hair, which grows at a pre­dictable rate and reveals the bear’s past “dietary sig­na­ture” — or what and where their meals were eaten, she says.

But it’s not quite that sim­ple. “It’s not just that a 50 per­cent salmon diet shows up as 50 per­cent salmon in the body,” Rode said. “Some gets routed toward body fat, some gets stored and some is trans­formed directly to energy. I need to under­stand how the bear body processes food before I can under­stand how dif­fer­ent diets may affect them.”

Ore­gon Zoo research con­tri­bu­tion
Dur­ing data col­lec­tion, the zoo bears par­tic­i­pated in what zoo staff dubbed a “surf and turf” exper­i­ment — switch­ing between marine and ter­res­trial foods. By com­par­ing this new data to USGS archive sam­ples from the Chukchi and South­ern Beau­fort Sea bear pop­u­la­tions over the past 25 years, Rode and her team may reveal the effects of this new meal diver­sity on polar bears.

We’re hop­ing to study their diets over time to explain poten­tial changes in resource use as a result of climate-​related changes in this sen­si­tive Arc­tic ecosys­tem,” said USGS research biol­o­gist Craig Stricker.

This project, con­ducted by the USGS Polar Bear Team, is part of the USGS’s Chang­ing Arc­tic Ecosys­tems research on the effects of cli­mate change on polar bears.

(Source: USGS news release, 20.04.2016)

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