Correction: An earlier version of this story incorrectly reported that the International Commission for the Conservation of Atlantic Tunas voted against establishing catch limits for blue and shortfin mako sharks. The commission did not take up the issue. This version has been corrected.

International negotiators took steps Saturday to protect silky sharks, a species that is vulnerable in the Atlantic Ocean, but rejected measures aimed at curbing the catch of other shark species targeted for their fins.

The delegates attending the annual International Commission for the Conservation of Atlantic Tunas (ICCAT) meeting in Istanbul also adopted a modest proposal that oversees the catch of Mediterranean swordfish, whose numbers are 50 percent below what is considered sustainable.

The commission governs the catch of species such as tuna, sharks, swordfish and billfish in the Atlantic Ocean and adjacent seas, along with the species that are caught accidentally in these fisheries. Environmentalists have frequently criticized the group, which has representatives from 48 nations, for not adopting scientifically rigorous policies, and for not cracking down on illegal fishing by its member states. On Saturday, advocates said delegates had responded to the science in some areas.

The International Union for Conservation of Nature estimates that as many as a third of all shark species face some threat of extinction, in large part because vessels target them to obtain fins for soup. It classifies silky sharks as “near threatened” with extinction.

“It is a great day for silky sharks,” said Elizabeth Griffin Wilson, senior manager of marine wildlife at the advocacy group Oceana. “ICCAT should be commended for its continued effort to protect the ocean’s top predators. Today’s decision to protect silky sharks is a strong step forward in protecting one of the most commonly found species in the international shark fin trade.” The new measure — proposed by the European Union, United States and Brazil — requires that all silky sharks caught in ICCAT fisheries be released, unless they are caught by developing coastal countries for local consumption.

For the second time, delegates declined to adopt a proposal by the European Union to protect porbeagle sharks because of objections from Canada, the only member of the commission that targets the species. The Commission traditionally operates by consensus, because if a country objects to a specific measure they can take exception as refuse to abide by it.

The IUCN identifies porbeagle sharks as vulnerable globally, and categorizes them as endangered in the Northwest Atlantic and critically endangered in the Northeast Atlantic.

“We made progress improving science, applying science to management measure, and improving monitoring and control,” said Russell Smith, deputy assistant secretary for international fisheries at the National Oceanic and Atmospheric Administration. He added that when it came to some of the measures delegates adopted, “Many did not go as far as the United States had wanted, but they are steps in the right direction.”

Sonja Fordham, president of the advocacy group Shark Advocates International, said that while the meeting’s outcome shows “much more must be done to effectively safeguard this and other exceptionally vulnerable shark species.”

Delegates rejected an effort by Belize, Brazil and the United States to require that all sharks be landed with their fins fully or partly attached, a measure aimed at curbing shark finning, after nations including China, Japan and South Africa objected. In a separate development Monday, the European Commission proposed an amendment to the European Union’s shark fin ban that would require all sharks landed have their fins attached.

On Monday, Hongkong and Shanghai Hotels became the first hotel company in Hong Kong to ban shark fin from its operations. The parent company of the Peninsula Hotels, Repulse Bay Complex and Peak Complex announced it will stop serving shark fin at all its group operations as of Jan. 1, though it will honor shark’s fin soup banquet requests made before Nov. 21 that are scheduled to take place next year. Shark’s fin soup is a fixture at weddings in Hong Kong hotels.

ICCAT also addressed a significant decline in Mediterranean swordfish, voting to require a minimum landing size, a limit on the size and number of hooks used to target swordfish, and a comprehensive reporting system for gathering sufficient data to assess the stock.

Maria Jose Cornax, Europe fisheries campaign manager for Oceana, called the decision “a half-hearted attempt to establish measures to protect overfished Mediterranean swordfish.”