"There is an enormous economic interest in catching and trading these species, and a Cites piece of paper is really a nuisance [for traders]."
Resistance from Asian countries, particularly Japan, to placing bluefin tuna on a protective list received most attention at this year's meeting.
Stocks of Atlantic bluefin tuna, prized as a sushi delicacy in Japan, have plunged more than 80 per cent since 1970, according to Cites.
Japan imports about 80 per cent of the catch, mostly from the European Union.
"It's been a difficult conference from a conservation standpoint, perhaps because of the economic environment," Tom Strickland, the US assistant secretary of the interior for fish, wildlife and parks, said.
"But the history of Cites is one built on supporting conservation over a period of time. We have a strong foundation, and often it takes several conferences to get things listed," he said.
Cites meets once every two-and-a-half years.
Amid the disappointments for conservation advocates, there were some successes.
|Trade interests have trumped proposals to step up protection for bluefin tuna [Reuters]
Kenya scored a victory with its proposal to combat the escalation of rhino poaching by placing the animals on a protective list.
Rhinos in countries such as India, South Africa, Nepal and Zimbabwe are killed by organised crime groups that control the smuggling of rhino horns to the far east of Asia, where they are sold on the black market for thousands of dollars, Cites says.
Calls by Zambia and Tanzania to relax a trade ban on elephant ivory were rejected and Porbeagle sharks, hit by overfishing in the Atlantic and Mediterranean, also won protection.
However, proposed protections for other sharks, which are caught as ingredients in shark's fin soup in Asia, failed.
And a US proposal to protect polar bears, which thrust the issue of climate change onto the agenda of the conference for the first time, was defeated.
Al Jazeera's Nick Clark, reporting from conference, said the Cites convention had seen big business and commercial interests win over conservation.
"Big business is the name of the game as a result the summit has failed badly," he said.
"The Cites convention has wrapped up and there is not a lot to shout about from the rooftops. All the proposals for marine species were rejected."