The Greek word used in the passage is gymnos, which means "nude." In that time and place, however, fishermen often worked nude since they usually only owned one garment. This would have been a linen tunic, often translated "coat." Since they did not want to spoil their only garment with fish guts, etc., they would often lay it aside where it wouldn't get spoiled, putting it on again when they were finished with the dirty work.
Another thing to keep in mind is that simple nudity in a non-sexual context was not usually seen as shocking or unusual, even when there were women around. The prophets in Israel often stripped off their clothing to prophesy, and when King Saul stripped naked and prophesied the people marveled...not at his nudity but that he was acting like the prophets. Micah mentioned stripping naked and howling in his writings, and in Isaiah chapter 20, Isaiah records that God told him to take off his clothes and walk around Israel completely naked for three years. Some have tried to dismiss this, stating that he took off only an outer garment, but it specifically says in that passage that he "loosed the sackcloth off his loins, which means he was taking off his undergarments as well. In the passage, Isaiah is doing this as a sign that the Egyptians and Ethiopians are going to be led away naked as slaves:
"So shall the king of Assyria lead away the Egyptians prisoners, and the Ethiopians captives, young and old, naked and barefoot, even with their buttocks uncovered, to the shame of Egypt."
If Isaiah was only taking off his jacket, so to speak, this passage would not make any sense. The problem I believe many Christians today have with passages like this that talk about nudity in a way that does not condemn it is that it makes people confused. In modern Christianity we have been infused with the Victorian idea that nudity is wrong, and this has influences our mores. The reality is that the Bible never states that nudity is wrong, though if used for the wrong purposes it can be. Jesus said that it isn't what enters into someone that results in sin, but what comes out of the heart. In the same passage he refers to the "lust of the eyes." This passage would seem to imply that simply seeing a naked person or being naked in a public place is not wrong, but lusting after a naked person is wrong. In the Old Testament, Bathsheba was not condemned for bathing on her rooftop, which was a very public place in the society of the time and place. It was the sin that resulted from David's lusting after her that was condemned.