How will the extinction of whale sharks affect humans?

Well, don't put on the black armband quite yet. The WWF rates the whale shark as "vulnerable" - meaning they could become endangered, but aren't there yet. No one is talking about extinction for them at this point. If they did become extinct (and I hope this magnificent animal never does), it is still, frankly, hard to see how that would affect humans to a great extent. Some peoples use them for food, but many other species can be substituted for that. They are essentially plankton and krill eaters, not top-level predators.