There are so many better fly fisherman than me that have written articles explaining the how to of mending so I am going to focus on the when and why I mend when fishing for smallmouth bass among other species of fish. One of my many gifts is the ability to solve problems and in my short fly fishing career I have realized that the majority of the time smallmouth are sitting on the bottom of the river or stream tucked behind some structure. So the problem was how do I get my fly to tick the bottom without it getting caught up on the bottom all the time.
When I first approached this problem I would tie my flies heavier. This turned out to be a mistake. My flies ended up getting snagged on the bottom very frequently and additional weight changed the movement and in particular how and at what rate the fly sinks. Once you have a the sink rate of your fly how you want it I recommend leaving the weight property the same.
We still have a problem to solve. Since we are not going to add more weight to our fly we then have to figure out another way to get our fly to tick bottom. There are three techniques I use to get my fly down deeper.
One of the biggest hinderances to a fly fisherman is line management. Line management becomes espescially important when using floating line. In fast moving water the current sweeps the line down stream applying drag on the fly. We can prevent this by thowing an upstream mend to place the line upstream of the fly. This allows the fly time to sink before the line starts applying drag to the fly and lifting the fly back up the water column towards the surface. The faster the water is moving the more often you will have to throw an upstream mend to keep the fly ticking bottom.
The great thing about fly fishing for smallmouth bass is that we often don't care about a drag free drift but I have found that getting the fly down and ticking the bottom is very important. One of the most productive patterns for me is a crayfish. I love using the crayfish hop which gets the fly dancing across the bottom. If you don't know how to crayfish hop then please read my article "The Power of the Hop." In faster water even my crayfish patterns are pulled up in the water column and mending is necessary. I have combined the hop and the mend together to conserve motion and allow the fly to hop and sink back down to the bottom. This technique has been absolutely deadly in bigger faster moving water.