From the crow's nest, some 60 feet (18 meters) above the waves, the horizon forms a perfect circle, and the visible world a perfect disc _ empty in all directions but for the sea.
Down below, the ship's captain is frustrated by that emptiness. He believes quite strongly that boats are fishing for bluefin tuna illegally, hastening what he fears is the species' demise. He wants to find those fishermen and stop them. But there are few blips on the ship's radar and few specks on the horizon save for the occasional NATO warship.
Paul Watson, captain of the Steve Irwin and founder of the U.S.-based Sea Shepherd Conservation Society, is mostly frustrated by what he sees as the Byzantine bureaucracy that fails to enforce its own fishing quotas and makes it very difficult for him to determine who is out on the Mediterranean harvesting tuna illegally.
His crew carries lists by of boats prepared by ICCAT, the International Commission for the Conservation of Atlantic Tunas. The list shows the quotas allotted each boat. But it's difficult to tell if a boat has met or exceeded its quota. And some boats are on the list but have no quotas assigned, which means they can help other boats fish but not do the fishing themselves _ and whether they are abiding by that can also be difficult to pin down.
So on Monday Watson ordered the Irwin to head south, into Libyan waters and make its way westward about 30 miles (48 kilometers) north of the coast. He hoped to find boats whose names were not on the ICCAT list at all, making them clearly illegal. Those he would confront, sending in divers to cut the nets and free the tuna.
"I call that aggressive nonviolence," he said in an onboard interview Sunday. "If property is used to break the law, we can destroy it."
In any event, Wednesday is the final day of the season, and anyone fishing for bluefin tuna after that is illegal, ICCAT list or no. And Sea Shepherd will go after them.
Watson, 60, is a man on a mission. He grew up in a Canadian fishing village, St. Andrews By-the-Sea, just across the border from Maine; the ocean left its mark on him from an early age. So, too, did a love for aquatic life.
When he was 10 years old, he said, he went swimming with beavers and had a wonderful time. When he was 11, he returned to the same spot but the beavers were gone, victims of hunters' traps. Watson says he set about releasing beavers when he could.
He founded Sea Shepherd in 1977, having grown frustrated with Greenpeace, which he considered oriented more toward protest than action.
Since then, the group has waged aggressive _ and highly controversial _ campaigns to protect whales, dolphins, tuna and other marine animals.
Japanese officials have called Sea Shepherd member terrorists, a charge Watson rejects.
"When the law isn't doing the job, that's when we need to intervene," he said. "If you want to call us eco-terrorists, arrest us or shut up. We don't break laws and we don't hurt people."
Watson has become known in the United States through Animal Planet's documentary series "Whale Wars." A film crew is on board the current tuna protection voyage, as well.
He first came to the Mediterranean in 1972, living on the beach on the Greek island of Rhodos, where he planned to work on his writing and become a poet. He writes poetry still, composing during his various voyages.
And he said he has seen since then the changes in the sea. "It's almost a desert now compared to what it was," he said.
But it is more than just the sense of mission that draws him here. He grew up by the water, and he was in the Canadian Coast Guard, and the Norwegian and Swedish merchant marines. He is at home on the sea.
"I'm doing what I want to do," he said.
Don Melvin can be reached at http://twitter.com/Don_Melvin