The $$$ and Sense of Minnows – Bruce Kania (May 2016)
If you work with nutrient impaired water, this is for you. But I want you to know starting out that your water may offer other challenges. So there could very well be some room for personal creativity too. But for nutrient pollution, I assure you the formula that follows does work. And the results are wonderful!
I’m doing this article in bullet points. Your time is precious. So is mine. So what follows is just data. No fluff. Sorry!
1. Prevent uncontrolled nutrients from entering your waterway, if you can. Know that any inflow water can carry these nutrients, even rain to a small extent. Intercept such water beforehand if possible, and expose it to surface area and circulation. Think terrestrial plants and trees if possible, but there are many other options too. Wetlands, strategic filter structures, the ground itself if your geomorphology allows, all of these and more are possibilities you may employ.
2. To maximize for cycling of nutrients that otherwise result in polluted water, integrate surface area and circulation into your waterway. The surface area can, and should, take many forms. Here’s some examples…cobble, gravel, sand, three dimensional structure underwater and at the water’s surface, like deadheads and boulders, perennial native aquatic vegetation, seasoned brush, floating islands. Circulation also comes in several forms…think about and take advantage of gravity flow, wind and fetch, vertical and horizontal aeration, floating stream beds. Surface area and circulation are primary steps. Your water must have these two factors in abundance.
3. Stay low in the circle of life. The surface area and circulation you have designed for will grow biofilm, food for minnows and invertebrates. This is a primary way to avoid monoculture of algae. Native minnows are usually best. I don’t know of any that do not feed on biofilm in its periphyton form. Likewise, the incredibly diverse repertoire of invertebrates that inevitably colonize periphyton add to the health of your water. They also serve to maximize the growth, volume, and health of your minnows. I know it is hard to exclude game fish from your waterway…but dedicate at least one water setting to minnows exclusively. This waterway will be incredibly productive, as in over 1,000 pounds of minnows per acre foot of water.
4. Every time your nutrients are eaten, only one tenth moves forward. Think of your dog…it eats ten pounds of kibbles, and only one pound becomes dog. The rest becomes manure, biogas and ultimately, other life forms. In practical terms, this means you can grow many more pounds of minnows from the same water that would only produce a couple pounds of big, game fish. And your job, as water steward, is to insure that inflow nutrients are cycling through your water. In other words, harvest. If your waterway is a Cul de Sac, and nutrients are not cycling out at the same rate or a higher rate than they cycle in, your water will die.
5. This is where it gets interesting. The suspended solids, colloidals, even solubilized nutrients within your water will bond to or at least become available to sticky biofilm (microbes and their residue) and the resulting life forms within periphyton. With the material that was blocking sunlight reduced, now sunlight, the motor of life, can penetrate deeper into your water. Life forms like diatoms, adapted to function in low light settings, can flourish at mid and deep levels within your water. The blend of biofilm, circulation and diatoms trigger an upward spiral relative to dissolved oxygen. The diatoms generate more dissolved oxygen than they consume, and they don’t die in massive blooms like other forms of plankton…like phytoplankton/alage/cyanobacteria. And all of this is happening deeper and deeper into your pond, which beforehand, given the usual nutrient overload, was dissolved oxygen starved.
6. Your pond is now producing top to bottom. Your water clarity is good and getting better. Minnows are being harvested at levels that match or exceed inflow nutrients. This means that harvest of aquatic vegetation is not as fundamental, although it is also a form of harvest and probably is needed over the first few years of such stewardship. And even though many casual experts believe that your waterway requires a zone without dissolved oxygen, know that the biofilm you have designed for includes such. Biofilm itself is stratified, and will include layers of aerobic, anoxic and anaerobic microbes. So the water in your waterway should not be anoxic or anaerobic. It should not disallow for the primary aerobic life forms, like fish. The nitrogen cycle is complete within the biofilm you have already designed for in bullet point #2.
7. The minnows are a terrific resource. They are valuable and can be marketed. They can be an excellent form of biological control of mosquito and midge larvae. Now you can improve quality of life on a landscape basis, without carcinogenic chemicals. You can limit disease vector insects, and correspondingly reduce risk of diseases like West Nile, Blue Tongue, in this region, and dengue fever, malaria, yellow fever and Zika virus elsewhere.
The key to this strategy are these two primary factors…surface area and circulation. Nature is insidious, it can not be stopped, and when given these two factors biodiversity is all but insured, short of some form of extreme environmental insult.
Today here at Shepherd we market high volumes of minnows commercially. We disperse others to minimize mosquito and midge. The rest are introduced into Fish Fry Lake. Minnows have a wealth of habitat in Fish Fry, but there are also a wealth of game fish present in Fish Fry. Today, Minnow Pond produces 1080 pounds of minnows on an acre/foot basis, while Fish Fry Lake produces between 26-28 pounds of game fish per acre foot of water. While the numbers are strikingly different, Fish Fry Lake is the most productive wild fishery in Montana that we know of. In fact, given waterways of over 50 acre feet, we know of no others that exceed ten pounds of fish per acre foot.
So our pocketbook benefits, our quality of life during mosquito season benefits, our sport fishery benefits, and finally, our water quality continues to improve.
Here’s how it shakes out in terms of return on investment:
A. Costs of floating streambed in minnow pond…$5,600. Operating costs, and related time/travel…$645. Minnow sales in year one…2,255 dozen at $3.50/dozen….$7,892
B. Mosquito reduction…difficult to quantify, but today, unlike the past, we can function in the evening in June without layers of chemical spray. No known incidence of West Nile disease or Blue Tongue mortality in the last three years, compared to as many as 19 whitetail mortality per season via Blue Tongue in the past, from this 340 acre property. This is the property’s second year of biological control via minnows. We see minnow over-winter survival in at least eight of nineteen perennial and ephemeral water features across the property.
C. Catch rate of game fish on Fish Fry Lake is less than one fish every two minutes, when fishing from shore. Boat fishing is typically even faster. Some aquatic vegetation harvest is still required on Fish Fry, but has reduced by ten fold compared to five years ago. Today, about 25 pounds of phosphorus is harvested, primarily in the form of fish from Fish Fry, against 11 to 14 pounds coming in. The lake is in transition, and is reducing inventory of phosphorus built up since the inception of agricultural fertilizer. Dissolved oxygen levels are consistently mid range stable, 5 mil/liter to saturated.
D. Nitrogen levels in outflow water are down to non detect, where in the past they could be dangerously high. Phosphorus levels average .02 parts per million.
Closing note…a largemouth bass population has developed in Fish Fry Lake. This is likely to reduce our harvest of yellow perch, black crappie, bluegill and red ear sunfish. However, corresponding size of pan fish should increase, although that has been our trend in any case, with perch up to two pounds. We see this as a natural progression for Fish Fry, and plan to enjoy the process! However, keeping game fish out of Minnow Pond is fundamental to our strategy.