Fishing Report: Steady flows at Lees Ferry could benefit food base
Those who frequent the Lees Ferry sportfishery have noticed something different during the weekends: Daily fluctuating flows have been replaced with relatively stable flows in order to test whether these stable flows can have a benefit to aquatic invertebrates — or fish food.
The steady weekend flows at Lees Ferry may benefit aquatic invertebrates at Lees Ferry. It is believed that daily fluctuating flows may reduce survival of aquatic invertebrates at this location and that steady flows may increase the number of bugs.
Early signs of potential increased invertebrate production are encouraging. Last Sunday numerous rocks were observed with a yellow line of midge eggs at the water line:
This has not been observed at Lees Ferry in a very long time. Hopefully we will see an increase in midge adults in about 6-8 weeks as the life-cycle of these eggs is completed and the adult midges emerge to lay more eggs. This, of course, would benefit the beautiful rainbow trout Lees Ferry anglers love to catch.
How fluctuating flows can stifle food base
Although Lees Ferry is an outstanding fishery, the fish food base (bugs) lacks diversity when compared to other similar tailwater fisheries. The standard for measuring the richness and diversity of the food base in trout streams is with an EPT score. EPT stands for Ephemoraptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies). Lees Ferry has few, if any, mayflies, caddisflies and stoneflies. Instead, rainbow trout and other fish at Lees Ferry rely on smaller food items like midges, blackflies and gammarus (scuds).
Many aquatic invertebrates have a short terrestrial adult life stage. These adult bugs lay eggs on rocks and vegetation at the waterline. After these eggs hatch, the larvae then live among the rocks and vegetation in the water. Daily fluctuating flows can be a problem if adult invertebrates lay eggs during high water and then the water level is quickly dropped. These stranded eggs are well above the water line and may not contribute to future generations of invertebrates.
Boat campers: consider weekend flows
Boat campers at Lees Ferry should be mindful of the flows. If you park your boat at camp on Friday night and the water drops, leaving your boat stranded, you might not be able to move your boat until the water comes back up on Monday.
Scott Rogers is AZGFD’s Fisheries Program Manager out of Flagstaff