Cordell:

I was wondering about the Baetis (Mayflies) on the Provo River and the Green River in Utah. I catch a lot of fish when the Baetis hatch. The fish seem to move up into faster water and start eating on the Baetis that are emerging, swimming, and floating on the surface. The question that I have is do you know why I stop catching fish when the hatch is over. Do you know if the insects just stop swimming, if the fish dont like to exert a lot of energy when nothing is hatching (water might be cold still) or maybe something else if happening?

A Mayfly

I am told, by a colleague of mine who is an avid fly fisherman, that you are probably fishing the wrong insect lifecycle or water column.

Mayflies have 4 main life stages (nymph, emerger, dun, and spinner) that are important to know for the fisherman. Nymphs spend their time under rocks and in the stream bed debris. Fish will feed on nymphs as they move from the rocks and drift down stream. This usually happens early morning to mid-day. Emerger is when the nymph begins to swim to the surface in order to molt before hatching into an adult. The dun, or adult mayfly, hatches and crawls on top of the water’s surface. Usually adult flight occurs mid-day during hatches and mating swarms take place. After mating takes place, the females fly back to the water to deposit eggs. Since adult mayflies only live for a day or two, the last life stage is also important for fishing and they are called spinners. Mayflies become weak after a full day of mating and laying eggs and they eventually fall to the water’s surface and die. Usually spinners are found at the end of the day, so as a fisherman, you’d change your style of fishing to match a spinner (meaning no drag on the line) if you were fishing in the evening. Knowing not only the insect’s life cycle, but also daily activity patterns in the stream/river is a useful tool for any fisherman.

So, to answer your question…you probably catch more fish during hatch because thats where all the activity is at that time, especially if your line is near the surface of the water. Both nymphs and fish are up and active at the surface of the water. After hatch is over, you’d want to switch your fishing technique so that you are fishing the lower water columns by the stream bed where all the next generation nymphs will be active and where the fish will be searching for meals.

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