Spring and Summer Pursuit of Kokanee: Two Big Words

by Gary Gordon, April 06, 2019

Sometimes you need to know more about stuff than rod, hooks, bait, corn, net and the smaller words we kokanee dudes know about. Let me introduce a couple of words that could make the difference between a fantastic day on the water and just a boat ride.

The first word is “Daphnia.” Kokanee love Daphnia. Daphnia make up to 90% of a kokanee’s protein diet. Yes, your favorite kokanee lake has Daphnia – likely tons and tons of Daphnia.

Daphnia are small freshwater crustaceans, commonly known as water fleas. They are called so due to the short, jerky flea-like movement they make while swimming. Their size ranges from 0.5mm to 6 mm. Males and females look similar, but the males have a smaller body and somewhat larger antennae.

Daphnia have a lifespan of approximately 10 to 30 days, but if their environment is favorable and free from predators, they can even live up to 100 days. Their primary source of food is phytoplankton. They also carry out filter feeding and consume bacteria, yeast, detritus, and dissolved organic matter – making them vital for a healthy lake environment.

Besides being a vital source of protein for kokanee, one other really important thing all kokanee fishermen need to know about Daphnia: Daphnia hate light. Hold that thought.

The second word is “crepuscular.” In this instance it describes the rays of light when first hitting the water. For the kokanee fisherman this is usually early morning, when the first rays of light come over the mountain top and through the trees to hit the water. When crepuscular light hits the water, it bends. Really !! The bending effect polarizes the light as it goes down the water column. Are you still with me?

As you just learned our friend Daphnia hates light. So while Daphnia have been happily grazing all night on the phytoplankton (the green stuff), they close up their eating shop as soon as that light hits the water. They then proceed down the water column to where it is dark. Of course, to get to the dark water, they have to do the gauntlet thing where the kokanee are waiting to slurp them up.

But the very cool (cruel?) thing is the effect of crepuscular light on the Daphnia. Daphnia have what is called an exoskeleton – the outer shell, so to speak, that supports the anatomy of the creature. When crepuscular light hits the water, it bends and polarizes. That polarized light then makes those Daphnia exoskeletons shine like the mid-day sun, making them very easy for the kokanee to see and target. The effect of the polarized light seems to last about 15 minutes. Polarized light does not penetrate the water column as far as does regular light.

So how can the kokanee fisherman take advantage of this oddity? For those who have followed my articles over the years, you know that I do my best to target a water temperature of about 54 degrees wherever that is in the water column. It is the optimal temperature for kokanee happiness, and 54 degrees is happiness for the food the kokanee eat. If I find that my target 54 degrees is say at 30 feet first thing, then when that crepuscular light is about to hit the water, I bring my downriggers up to about 18 to 20 feet. This is where the kokanee will be lingering to snatch up the now visible Daphnia. Invariably, the action is fast and furious. Most of my doubles occur during this time slot.

As the time slot for the polarized light shuts down, their exoskeletons lose the glow effect, and the Daphnia become more invisible to the kokanee. You will know when that happens. The bite shuts down, and you need to return to the normal fishing depth.

This technique is successful for most everybody in the early part of the season. But it works really well throughout the season if you are fishing the northern lakes where the kokanee fishing never really drops below 30 feet.

Next: What happens to light in the water column and how you can take advantage of that.

Gary S. Gordon, owner Fish With Gary Tackle Co.

© 2109 Gary S. Gordon


3/31/2019 9:19:59 AM
That is one of the best explanations I have read on the Daphnia Gary. When fishing Roosevelt the huge "schools" of Daphnia will show up on the sonar as haze leading one to believe there is something wrong with the settings on the sonar. I have found both
trout and kokanee feeding heavily on the Daphnia. Green goo in the fishes mouth and poop are a huge clue that's going on. They eat so much it's one Daphnia in and one out....Alan
Leave a Comment: