Countries involved in bluefin tuna fishing need to do more to protect the collateral killing of sharks, an environmental group said Tuesday. Three-quarters of migratory shark species that inhabit bluefin fishing areas are threatened with extinction, the Oceana group warned the International Commission for the Conservation of Atlantic Tunas (ICCAT.) \"The fishing countries of the Atlantic can no longer ignore that shark populations are being decimated by ICCAT fisheries,\" Oceana manager Elizabeth Griffin Wilson said. Representatives from dozens of bluefin tuna fishing nations are meeting in Turkey to discuss ways to improve protection for the endangered fish, savoured by many sushi eaters for its firm meat. Oceana wants the 48 commission members to prohibit the retention of endangered or other particularly vulnerable species, including porbeagle and silky sharks. The commission already has introduced protections for the bigeye thresher, hammerhead and oceanic whitetip sharks. The US Pew Environment Group wants fishermen to use new materials that allow sharks to escape, such as nylon fishing lines that can be severed by a shark but not a tuna. \"Banning wire leaders and not allowing vessels to retain certain species would help reduce the vast number of sharks caught and killed in Atlantic fisheries,\" said Pew shark campaign manager Jill Hepp. Pew says 73 million sharks are killed each year, mainly for their fins, which are used in soup in some Asian countries.