Countries involved in bluefin tuna fishing have agreed to make more effort to protect a rare species of shark and curtail illegal fishing.

Delegates of the 48-nation International Commission for the Conservation of Atlantic Tunas Conference meeting Saturday in Istanbul decided on a measure mandating that silky sharks accidentally caught in fishing gear must be released alive back into the sea.

Tuna boats often snare the species by accident and then sell them for their fins. Now they will have to throw them back into the water. Poor coastal communities that hunt the shark for domestic consumption will be excepted.

Elizabeth Griffin Wilson of the environmentalist group Oceana in Washington said the 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.

Delegates also strengthened measures to combat illegal fishing. They agreed on a plan to introduce a new electronic bluefin-tuna-catch tracing system to replace paper documentation which is easier to falsify. The system will track the rare fish species from the place where they are caught at sea to the market.

Research shows that catches often have been far higher than fishermen have declared.

Government delegates also passed a minimum legal size for Mediterranean swordfish, whose numbers are below what is considered sustainable.

Environmentalist have welcomed the new measures, although some say more marine life protection is needed.