Find the food, find the fish
To keep abreast of fishing conditions at Eagle Lake, I check in with guide Doug Wilmes from Susanville.
In season, Wilmes fishes regularly on the lake and can usually take fish any week of the year. He has taken his fishing seriously enough to scuba dive the lake to get a better understanding of what goes on beneath the surface.
His report from last weekend was that the fish were biting well at the deeper south end of the lake at depths of 25 to 35 feet on trolling flies in combinations of hot orange, tangerine and gold. The key was to fish deep and slow with bright lures.
This report was nothing out of the ordinary until he said, “The fish were feeding heavily on krill. When he put them in the boat they were burping up gobs of these tiny shrimp.”
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His comments piqued my interest, and with further questioning, he described the organisms the fish were eating as one-sixteenth inch and a “green slime” when it came from a trout stomach. This is an accurate description of daphnia. His term “krill” refers to a small ocean shrimp, but it’s not too far off from daphnia.
Daphnia is a crustacean, a distant cousin to crawdads and shrimp. They live in most freshwater lake environments on the planet. They are most easily found as fish food in aquarium stores.
Daphnia are the next step up the food chain from algae. They eat the algae and are in turn eaten by fish. The reason to get into this topic is the axiom: “Find the food and you will find the fish.” Understand daphnia behavior and you have one more piece to the lake-fishing puzzle, especially during the heat of summer.
Daphnia are strongly adverse to sunlight and will swim vertically down dozens of feet quickly to avoid sunlight. Their food source, algae, grows with sunlight at the top of the water column, which is where they must go to feed.
But on those days with alternating dark clouds and sunshine, they yo-yo up and down the water column as the light comes and goes. Despite their ability to move up and down, they do not swim laterally. They drift on the currents within a lake.
Rainbow trout, as well as kokanee, feed heavily on daphnia during the heat of summer when they are most abundant. Daphnia have a life cycle of about two weeks between birth and reproduction, living for many weeks with multiple broods. There are major die-offs in the fall as the water chills. Eggs winter over and renew the populations in the spring. There are two basic color schemes to daphnia, crawdad/scud orange and green.
In many lakes, trout have good supplies of insects in the spring. But by midsummer the insects are less abundant, as the daphnia are reaching their seasonal peak and thus become a significant food source. They congregate in “blooms” and trout swim through the bloom filter feeding. The fish will follow the blooms as they rise and fall in the water column and drift with the currents.
From a practical perspective, photosynthesis penetrates water to 25 feet. The bulk of the weeds and algae will be from 0 to 25 feet. During the day daphnia will go down away from the light and the fish will follow.
Ask guides what depth they troll and it is no coincidence that they often mention the 25- to 40-foot zone where the daphnia seek refuge from the light waiting to go back up to feed in the evening. Daphnia are not the only motivation for trout depth. Temperature is a major factor.
So what does an angler do to catch fish feeding on daphnia? They are too small to put on a hook. A fly is impractical to tie. And how could you expect a trout to eat your spec among tens of thousands in a bloom?
After generations of trial and error, fishermen have found that trout will react to lures and flies in bright colors that mimic the daphnia colors, hot orange and/or chartreuse. In oxygen-poor water, daphnia build up hemoglobin that gives a reddish-orange hue to the blooms. They also can have a green hue based on the algae they consume. The second most important color scheme for anglers is bright green. Fluorescent chartreuse is another color that daphnia feeding fish will react to aggressively. One of the most popular lure color schemes is “fire tiger,” which combines chartreuse and orange.
This brings us back to the fishing report from Eagle Lake last weekend.
Daphnia-feeding trout were consistently hitting trolling flies fished slow and deep. Many streamer fly patterns worked if they included hot orange or tangerine with gold flash rigged behind a “Wigglefin Action Disc” to give it some movement. Dick Night spoons in gold with orange tape also produced.
For more information on Eagle Lake, give Wilmes a call at 249-1478.
Denis Peirce writes a weekly fishing column for The Union, the Sun’s sister paper in Grass Valley. He may be reached at firstname.lastname@example.org.
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