Fish Fry Lake – Why is Fish Productivity So High?

Let’s clear up a misconception here. Some folks believe that eutrophic or hyper-eutrophic lakes mean high fish productivity. This is not so. Nutrient-rich lakes  invariably short circuit. The nutrients have nowhere to go, nothing to fertilize. They stack up, accumulating in the water column.  Then such lakes run out of dissolved oxygen. As they slip into anoxic or anaerobic status, their actual fish productivity diminishes by more than 80%.

Conversely, in a waterway managed for health, we cycle excess nutrients through the food web and take them out of the water by harvesting them. Ideally this is in the form of high-order species like game fish. But the form is less important than the fact that it’s happening. When more nutrients are cycling out of a waterway than are coming in, the waterway is in Transition, moving back towards a pristine state.  We can influence this process.  The name we have given it is “Transition Water”.

Factors to Transition Water

Dissolved oxygen, sunlight, surface area and circulation are the four variables we manage to influence a waterway’s fish productivity.  But many pond managers believe they can bypass nature by feeding their fish, instead of relying on their waterway’s natural food web. Fish feed is a form of added nutrient. Even if the fish eat it all, they still excrete nutrient-rich guano that gets added to the inflow and sediment nutrients that are still arriving. This is a formula for an eventual fish kill. The waterway is in a downward spiral.

Take any one of these four key factors and improve it and your waterway’s health will improve. So will its productivity. Do all four – then add the vital element of strategic harvest, and you will have a Transition Waterway.

Harvest

If you can cycle more nutrients out of your water than are coming in, water quality will improve. You can see it reflected in water clarity, abundance of life, health and growth rate of the fish, and of course, the absence of toxins in your water.

We work on all four factors in Fish Fry Lake, albeit in fits and starts. We harvest at a level that matches the inflow nutrient load. Here are some of the results:

Dissolved oxygen stays consistently high. Diatom-based periphyton thrives on floating islands and the stream beds bump up oxygen levels. Sunlight extends deep into the waterway, triggering diatom growth.

Bio-complexity continues to expand, with life forms like native fresh water sponge colonizing the underside of floating islands, and wild flowers like Indian Paintbrush occurring on top. Both add surface area and, in the case of fresh water sponge, filtration, which contributes to improved water clarity.

Circulation within Fish Fry Lake is associated with inflow/outflow at a rate of 65-80 gallons per minute. This flow is generated by wind and wave action and the mechanical action of two floating stream beds. The combination results in suspended solids and colloidals being filtered onto several places. These include the biofilm covering stems and leaves of aquatic vegetation; the perimeter of rock, cobble and deadheads designed into the lake’s benthic zone; the surface area associated with roots growing through the numerous islands; and the saturated filter matrix material of the islands themselves.

Good and Plenty

Harvest also takes numerous forms. For example, we annually harvest from 6,000 – 8000 fish from specific age classes from the lake. We also harvest other biota, like the invasive American Bullfrog, and aquatic vegetation. The fish are cycled out of the lake, and/or into bigger class fish within the lake, which in turn are harvested for human food. The bullfrogs are also harvested for human consumption, and the aquatic vegetation is cycled into worms and worm castings. Some of the worms are cycled back into fish, but most are retained and generate valuable worm castings which are cycled into our property.

Doing all of this on a planned basis, instead of happenstance, is challenging. But the “theme” is valid. Even if you can’t afford to “quantify” your actions, when you do improve all four of these variables, your waterway gains new life. See our Lake & Pond Management section for more information.