SINGAPORE: A Singapore casino resort's acquisition of dolphins from the Solomon Islands for its marine park contributed to the depletion of the species there, an animal welfare group said on Friday.

The Singapore-based Animal Concerns Research and Education Society (Acres) released a video on the depletion of the Indo-Pacific bottlenose dolphins from the islands as it intensified a campaign for Resorts World Sentosa (RWS) to release the animals.

RWS acquired 27 dolphins from the Solomons between 2008 and 2009 despite the availability of information "advising against the purchase", Acres said in a statement.

It cited a report by the International Union for Conservation of Nature, which said that catching dolphins from the islands would be detrimental to the survival of the species there.

The dolphins, now numbering 25 following the deaths of two, are currently in the Philippines for training, and will be shipped to the RWS marine park in Singapore sometime next year. The park is set to open without them later this year.

The large mammals were at the center of a legal tussle this week after a Philippine court temporarily blocked their transport to Singapore following a civil suit filed by animal rights activists.

They alleged that the dolphins' capture from the Solomon Islands violated an international treaty on the trade of endangered animals and plants.

However, the Philippine government said on Thursday it has approved the export of the dolphins after the ban on transporting them was lifted.

Resorts World "should have performed due diligence before they acquired the dolphins", said Acres Chief Executive Louis Ng, who called for the animals to be released back into the wild.

There was no immediate comment from RWS on the Acres allegation.

But in a statement issued on Wednesday relating to the Philippine court ban said: "Our dolphins are doing well under the care of our team of experienced experts, and we look forward to welcoming them to Singapore."

It also disputed allegations that it had contravened international treaties in acquiring the dolphins.

It accused the group that initiated the court action in the Philippines of "perpetuating the same falsehoods that we had repeatedly made numerous clarifications and corrections to in the past".