Soft hackles prove deadly during the less prolific Mataura hatches when fish may rise a couple of times and then disappear. In these situations there are enough mayfly about to get them rising sporadically, but not enough to keep them locked at the surface, or feeding within the confines of a determined feed lane.
The fish are still there: there just isn't enough food on top for them to concentrate here.
Carefully wade into position wide of and / or just below the rise. With a longer, light leader, plop your pair of small soft hackles 45 degrees upstream, above and across of the rise form. Remember in these conditions, where fish are lifting from the bottom that their riseform is often significantly downstream of where he sits.
Allowing the flies to sink briefly, as they approach the rise area a simple long draw with the line hand will move your team through and across the current where the fish sits. Be prepared for the tug.
We are doing a couple of things here: firstly we are making our flies stand out from the naturals by drawing them across the current, rather than with the current where all the others are drifting. This will catch the trouts eye and if he sees your fly he has but two choices: yes or no.
Secondly we are improving the hookup in a situation where many fish will eat rather softly (ask any mataura angler how many fish they 'pluck' rather than hook in sparse hatch situations and you will know what I'm saying). As we draw the fly on an angle downstream or across, we are maintaining constant tension on the line. Any fish that eats, stands a good chance of being hooked, as you effectively pull the fly into the corner of his mouth.
You will find in sparse hatch situations, pulling a team of soft hackles will produce far more hookups than persevering with the good old emerger in the surface film.