Who can harpoon a dugong from a mile away? Ned Land can, Ned Land can. Ned Land's got some special eyes, see. He's got perfect vision, which comes in pretty handy for this hunter when he wants to spear food or enemies (or enemies that later become food).
But there's more to Land's 20/20 eyesight than meets the eye (hee hee). This guy's vision is a stand-in for his unwavering practical insight. His understanding of Nemo and the whole Nautilus situation is perfectly clear from the outset: he knows Nemo's a weirdo and he wants off that sub as soon as possible.
While Arronax's got his head so far into his books that he can't see the danger they're all in, and Conseil is too busy agreeing with his master to be concerned about anything else, Ned is watching out for the whole gang's survival. Good thing, too, because he often ends up saving the other guys with his super manly fighting skills.