LISBON, Portugal (AP) — Greenpeace is warning about overfishing of endangered sharks in the North Atlantic, often by Spanish and Portuguese boats.

The group has published a report Thursday arguing that tens of thousands of endangered sharks are killed each year because of a lack of measures to protect them in international waters.

It claims that vessels, which go in search of swordfish in the North Atlantic catch, by weight, four times more sharks. However, it notes that the figures are disputed.

The Spanish and Portuguese longline fleets are a key focus of the report. Greenpeace says their cables with hundreds of baited hooks attached along them end up netting sharks.

The report's publication coincides with a pole-to-pole voyage by the Greenpeace ship Esperanza as part of the group's campaign for better ocean protections.