Environmentalists and five fishing boats are engaged in close maneuvers at sea as activists try to determine whether the boats' fishing is legal, while the boats work to protect their catch.
Some of the fishing boats are sidling alongside their nets holding tuna.
Another is chasing the Steve Irwin, a ship owned by the Sea Shepherd conservation society.
A Sea Shepherd spokesman said early Saturday two of the boats are not allowed to fish legally, according to a list prepared by ICCAT, the International Commission for the Conservation of Atlantic Tunas.
Divers on the Steve Irwin are standing by, prepared - if they can - to go into the water and cut the net to free the tuna.
The action is taking place in the no-fly zone north of Libya.