The Vancouver Aquarium is mourning the death of another marine mammal after a rescued harbour porpoise named “Daisy” died on Thursday.

The aquarium wrote in a blog post that they became increasingly concerned about Daisy’s well-being after they noticed a change in its behaviour earlier this month. Staff started providing around-the-clock care for the harbour porpoise after its health took a “downturn” this week.

The Vancouver Aquarium said that results of a preliminary necropsy showed that the cetacean had a pulmonary disease.

The aquarium’s Marine Mammal Rescue Centre rescued Daisy when it was only a month old in August, 2008.

The news of the porpoise’s death comes at the same time the aquarium announced it was submitting a legal challenge to overturn the Vancouver Park Board’s bylaw banning the facility from acquiring new whales, dolphins and porpoises.

Daisy’s death leaves the aquarium with two remaining cetaceans, a false killer whale and a Pacific white-side dolphin.

The aquarium has come under fire in recent months after the deaths of two resident beluga whales in the fall. The belugas, a mother and daughter named Aurora and Qila, died from exposure to a toxin. The exact substance has not been identified.

With files from CTV Vancouver