Tasul, one of two polar bears at the Oregon Zoo and one of the oldest of the ursine creatures in captivity, was euthanized Friday morning due to complications arising from ovarian cancer.

She would have been 32 in about two weeks and her death leaves Nora, a hand-raised cub who was relocated to the zoo earlier this year, in a precarious situation as the zoo's sole remaining polar bear.

Tasul was born Dec. 1, 1984, at the Riverbanks Zoo in Columbia, South Carolina, and came to Portland two years later along with her twin brother Conrad, who died in July as the oldest male polar bear in captivity.

"It's always excruciating to lose an individual that you are so close to," said Amy Cutting, the marine life curator at the zoo, who said Tasul had developed an especially close relationship with her keepers. "I've never had one of these that was easy, but we don't let our animals suffer here and we're just glad we could give her a pain-free death."

Throughout their nearly three decades at the zoo, both Tasul and Conrad made history. In 2012, Tasul became the first captive polar bear to voluntarily have blood drawn without first being anesthetized. The breakthrough was made possible by extensive training done by her dedicated trainers, Nicole Nicassio-Hiskey and Amy Hash, and some creative cage design including a special opening in which Tasul would willingly present a paw for blood to be drawn.

Tasul also became the first captive polar bear to wear a collar, which contained two accelerometers that tracked her movements while swimming, eating and playing. The data collected helped inform the research of biologists tracking polar bears in the wild who face threats due to climate change, including retreating sea ice.

Beyond giving blood and wearing a research collar, Tasul also performed other tasks previously unheard of in captive polar bears, accepting eye drops and having her teeth brushed among them.

It was that voluntarily-given blood that first raised concerns about Tasul's health in October. A screen of the sample showed the geriatric bear was suffering from the early stages of kidney and liver failure. A follow-up ultrasound showed that Tasul also had developed an aggressive type of cancer on one of her ovaries.

The zoo brought in a specialist and Tasul went in for surgery Friday morning. The hopes were, Cutting said, that the cancerous ovary could be removed and a closer inspection would show that the carcinoma hadn't spread.

But that was not the case.

"An ultrasound doesn't give you a full picture, especially in an animal this large," Cutting said of the nearly 500-pound bear. "We were hoping that we caught it at an opportune moment, but it had spread.

"It wasn't in her best interest to wake her up and have her live out what could have only been a period of weeks or months, especially given the recovery period she was facing," Cutting said.

While Tasul's death certainly marked a sad moment for the zoo and the staff who became close with Tasul, her keepers were already reminiscing about her lively personality soon after she was euthanized.

Cutting described Tasul as a bit of a mischievous prankster. If she felt like her keepers weren't paying her enough attention, she would wait until they turned away and loudly knock a toy off the top of her enclosure, scaring Cutting herself on more than one occasion.

"It was entertaining for her," she said.

For Cutting, though, Tasul's death provided an opportunity to reflect on her entire time at the zoo and the legacy the elder bear left behind. Cutting said she couldn't be more proud of the relationship Hash and Nicassio-Hiskey developed with the Tasul.

"It was incredible to watch Tasul blossom," she said. "Her training became more of a conversation and she just had such a great relationship with the staff. They hugely improved her quality of life here.

"When the keepers talk about her, they talk about her legacy," Cutting continued. "She really revolutionized the way we think about polar bears in captivity."

There's no time to spare in implementing the lessons Tasul taught to the zoo staff, as her death leaves Nora, the polar bear cub relocated to Portland from the Columbus Zoo in Ohio earlier this year, as the zoo's sole remaining polar bear.

Nora's situation was already complicated — she was hand-raised in Ohio after her mother abandoned her in the den for extended periods of time. Cutting and the rest of the bear keepers in Portland were hoping for a seamless introduction between the 1-year-old cub and Tasul, but the fact that Nora had only interacted with humans for much of her existence made her skittish around the elder bear and it was taking longer for the bears to become comfortable around each other than their keepers had hoped.

"She still has a lot of overall anxiety," Cutting said of Nora. "I think we were a little overconfident in our ability to normalize her behavior."

Still, the younger bear had been making good progress over the last few weeks, showing more confidence in exploring the three outdoor enclosures she has access to outside of public view. On Friday morning she was wandering between two of them, taking breaks to lick peanut butter off of a trash can lid and at one point sticking her head inside an orange traffic cone, essentially wearing it like a hat.

Cutting has said repeatedly that Nora very much needs to "learn to be a bear," as she's really only had interactions with humans. But with no other bears left at the zoo to act as a mentor for Nora, the cub is at a bit of a crossroads.

The zoo was already planning to bring in a behavior specialist in the coming days to formulate a plan to socialize Nora, but that input will take on extra significance now as Nora learns to cope with her new environs alone.

"We have to reboot and make a new gameplan," Cutting said. "The next year is definitely going to be a challenge for her."

The hopes are that Nora can be socialized to the point that, once she reaches the age of 2 when polar bears typically leave the company of their mother, she'll be ready to meet another bear of the same age who might be available to move to Portland.

In the meantime, however, Tasul's legacy and the things she taught her keepers at the zoo are already paying dividends for the younger bear.

"We are going to take everything we learned from Tasul and apply it to Nora," Cutting said. "She definitely is going to need our help."

— Kale Williams

kwilliams@oregonian.com

503-294-4048