A rare porpoise has died in Mexico after being captured as part of a rescue effort for the species.
There are thought to be just 30 vaquitas - the world's smallest porpoise - left in the wild.
Mexico's environment minister had said that Saturday's capture of a mature female was "a great achievement that fills us with hope."
However, he later said on Twitter that the captured vaquita had "suffered complications" and died.
The vaquita marina is known as the "panda of the sea" as it has distinctive markings that circle its eyes.
In recent years, there have been concerns that it is on the brink of extinction due to illegal gillnet fishing in the Gulf of California.
The Mexican government and conservation groups have launched a plan to save the species, involving capturing as many as possible and taking them to a protected marine reserve.
The vaquita caught on Saturday was a mature female and it was the first animal of reproductive age captured by the project.
The International Committee for the Recovery of the Vaquita, which is involved with the programme, said that although the conservation operation was risky, scientists warned that "the risk of extinction due to mortality in fishing nets was much greater than the risk of rescue efforts."
The vaquita has been nearly wiped out by gillnets used to fish for the also-endangered totoaba fish.
The swim bladder of the totoaba is a delicacy in China and can fetch as much as $20,000 (£15,000) per kilogram.
In June, the Mexican government announced a permanent ban on gillnets in the vaquita's habitat.
The government has committed more than $100 million (£76 million) to save the vaquita, as well as supporting the fishing community.