A: There are several reasons why you adjust the hook size of a pattern. If you want the fly to sink deeper, you may want to use a larger hook or one with a heavy shank. The opposite is true when you fish for bonefish in heavy turtle grass. In that case you should use a light wire hook and perhaps one that's a size smaller than normal. In either case, it's vital that the gap of the hook is large enough to clear the pattern and ensure a good hookup. The strength of the target species determines how heavy-duty the hook should be. Since small hooks tend to be light, you might have to go to a larger hook just to hold a small but powerful fish. The style of pattern also determines hook size. A sand eel pattern that has a sleek body will not draw as many strikes if you use a large hook since much of it would be visible to the fish. To create a more realistic fly, you'll also want a slightly longer hook shank for longer patterns.