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

The group 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.

Spanish and Portuguese longline fleets working in the North Atlantic are a key focus of the report. Greenpeace says their cables with hundreds of baited hooks along them end up snaring sharks as well as swordfish, which are the ostensible target of the fleets.

The group said that the vessels catch four times more sharks than swordfish by weight, citing a report last year by the International Commission for the Conservation of Atlantic Tuna, which oversees conservation and management of ocean species.

Greenpeace notes, however, that the shark catch figures are disputed.

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