NEW BEDFORD, Mass. (WPRI) — Buttonwood Park Zoo is mourning the loss of one of its Atlantic harbor seals.

Yellow, one of the zoo’s oldest residents, passed away less than a week from her 40th birthday. The Atlantic harbor seal was rescued from a Cape Cod beach back in 1983, according to the zoo.

The zoo’s veterinary team was carefully monitoring Yellow for age-related illnesses, and noticed she had stopped eating and was lethargic.

Due to her advanced age, poor prognosis and deteriorating quality-of-life, the veterinary team made decided to humanely euthanize her.

“It was an incredibly difficult decision; one that we did not come to lightly,” Buttonwood Park Zoo Director Gary Lunsford said. “Yellow was a wonderful ambassador for her species and beloved by so many.”

The zoo described Yellow as being “…very sweet, and a little sassy.”

“There are so many things that we loved about her and will miss forever – like her impatient little snorts when we were taking too long with the fish that she loved so much,” said Kristy Kaeterle and her twin sister Kerry Silva, who cared for Yellow for more than two decades. “She also had impeccable timing, knocking the pool brush out of our hands at just the right moment bringing a laugh from us, every time.”

(Story continues below gallery.)

Yellow also had a quirky habit of napping at the bottom of her pool, much to the concern of passersby.

“Guests would constantly ask us, ‘What is she doing?'” the sisters recalled. “We would assure them that she was just taking a little nap.”

She was also known for her unique artwork, which was featured annually at the zoo’s Art Gone Wild Auction.

“If you have a seal flipper print in the shape of a flower – cherish it. It was her specialty,” Kaeterle and Silva said. “She taught us many things over the years, but one of the most important lessons we learned was the importance of trust in a friendship.”

Yellow leaves behind Blue, her sole living offspring, who was born at the zoo back in 2003.