Building the Perfect Trout Fishery (1 of 3)

The world is your oyster, but where you start? You can break ground anywhere, ideally by a river, but remember everything happening upstream eventually leads through where you decide to set up shop. Right off the bat, geology and geography set the stage for everything else: high elevation is good for stream temperatures, you'll likely have snowpack and continual snowmelt. On the other hand, cold temperatures limit growth throughout the food chain with shortened growing seasons, and we all know you're after growing big fish. If you're high up in the basin, water has less time to accumulate different minerals and nutrients, which only accumulate downstream. Fortunately, trout are hearty creatures, and stream temperatures are more important for their growth than what elevation you find them.

Rock composition also factors into how a river takes shape, influencing river gradient, and water quality. Igneous rock may be lower in pH, and if too acidic may limit nutrients and growth throughout the ecosystem. Meanwhile, sedimentary rock, specifically those with carbonate, like limestone, buffer against acidity which can better support dense populations of aquatic life. Carbonate rocks also provides calcium, needed by stream algaes, as well as to replace growing invertebrates exoskeletons. So, more calcium, more bugs. More bugs, bigger fishies. But as with anything in nature, only up to a point. We'll pick this back up in the water quality section.

Next, consider the connectivity of your site within the watershed. Are there tributaries that feed into a larger system? Tributaries increase habitat connectivity, habitat diversity, and provide multiple sources of water. Migrating fish may run out of lakes or from large stream into small tributaries to spawn or take refuge from hot downstream temperatures. This makes tributaries important for the trout life cycle.

Other watershed considerations may include lakes, and dams, both natural and artificial. They could supplement water supply during low winter flows, or provide cool temperatures during high summer heat. In arid environments, beaver complexes help a watershed retain water longer throughout the year, support riparian habitat, groundwater recharge, and in case of wildfires buffer the heat effects in the riparian corridor surrounding streams. In wet environments, they can create unwanted blockages and reshape rivers in unexpected ways. So you may turn to reservoir construction. Dams impair habitat connectivity, but again can buffer stream temperatures during summer and winter. They can trap sediment from upstream, preventing fine grain particles from smothering essential trout habitat... yet require constant attention. Modern trends in reservoir installation lean on off-channel construction, siphoning off water from the stream during periods with extra flow, and returning flows when appropriate. These dams offer downstream benefits without as many drawbacks as a traditional dam. But, make sure to outfit an off-channel dam with mesh grating to prevent fish entrainment, they might chase the flow.

Any dam will still be susceptible to evaporation, where water is lost off of the surface of the reservoir. If you choose an arid site, make sure to factor in dam evaporation as lost water. You may alternatively consider a natural dam, like from beavers, to better retaining water in the system. Beaver dams aren't without drawbacks though. They may harbor trout predators (like otters), or impair fish movement at low flows.

Your perfect trout fishery may employ beavers dam in upstream tributaries, and simultaneously maintain an off-channel dam adjacent to the mainstem. We'll dig into how we might manage such a dam later on.

Our last consideration, land use. Short of optimizing the entire drainage basin for fishing, other nearby land owners may use their land with different intentions. Upstream agriculture risks overloading nutrients and pesticides into the stream system, considered a major source of pollution. Though nitrogen and phosphorus are essential for primary production in algae and plants, too much will knock your trout fishery out of whack. Also watchout for pesticides, which are especially detrimental to stream macroinvertebrates.

Nearby civilization may be equally problematic, avoid upstream wastewater treatment outflows which can alter downstream chemistry and temperatures. In fact, pharmaceutical drugs don't often filter out in wastewater treatment operations leading to odd effects in aquatic species... Like hermaphroditic fish caused by flushed birth control drugs. That's not ideal sustaining a reproductive population, and not suitable for the perfect fishery. Similar to agriculture, cities use lots of water, which may divert needs away from your fishery.

Look for systems that minimize road crossings over rivers, or roads running alongside rivers. In the case that road crossings are necessary, trout friendly culverts are worth the extra costs. But riverside roads increase pollution into streams, and now evidence suggests that chemicals from tire rubber harms fish like salmon and steelhead when rain washes particles into nearby waterways. Finally, the big red flag. Extractive mining. Acid mine drainage can lead to heavy metal introduction into streams, which is highly detrimental to stream life. Even closed and sealed mines leak, needing extensive remediation. Avoid these areas.

Next we should consider climate, precipitation, and vegetation.

To keep things simple, the ideal climate would keep stream temperatures in the ideal range for trout. Though this varies from species to species, generally the window is water temperatures between 50-65°. Though it might be enticing to chase areas of high precipitation -- looking to secure stable flows, you won't find many sustainable trout fisheries in tropical latitudes (where precipitation is most predictable). Search out sites in temperate zones, with defined seasonal variation. In these zones, temperatures range from around -20° to 90°, seasonally. Seasonality is essential for triggering important life stages for trout, and macroinvertebrates. Streams also depend on terrestrial nutrient pulses, leaf litter deposited during autumn helps introduce new nutrients for bacteria, fungus, and grazing invertebrates.

In temperate zones (approximately 23.5° to 66.5° N/S of Equator), precipitation as snow can be important for sustained summer stream flows. Snow can accumulate and stockpile better than any pulse of water provided by a brief storm. Search for areas with perennial upstream snowpack, or consider how other water retention systems would need to be implemented to make up for natural shortcomings. Be careful though, snowpack isn't constant and varies year to year. Alternatives may include spring fed streams, tailwaters, or regions with greater annual precipitation.

Don't forget vegetative cover, another variable tied to climate. Vegetation, especially riparian plants help stabilize stream banks from erosion, provide shade and overhead cover (habitat trout seek out), even filter water. Trout can live in many places, from grassy plains to forested canyons. Decorate as you like. Hoppers do love grass though.

Though the climates of the US South, New Zealand, and US West drastically vary, these three regions are responsible for growing the largest brown trout, larger than in their native range. This may suggest climate needs must pass a certain threshold but beyond that, lots of variability is acceptable.

Without water, there is no trout stream, so we need a reliable supply year round. That starts with snowpack and precipitation. In temperate zones, approximately 23.5° to 66.5° N/S of Equator, precipitation averages between 30-59 inches annually, this should be a good starting point to find your site. Small streams likely can't support the sizes and populations of large fish, while vast massive rivers may be difficult to fish or even manage a fishery. But we'll get into population dynamics more later.

Areas with greater annual precipitation may experience less fluctuations in flow throughout the year but if selecting sites in arid regions avoid the temptation to indulge in dam installation to control and regulate flow throughout the year. Many species, trout and macroinvertebrates, rely on the annual runoff pulse. This flush can remove fine sediment particles, opening up new trout spawning habitat, or foraging habitat for macroinvertebrates. Many desirable invertebrates also rely on runoff to cue their emergence, like with the Salmonfly. Installing dams can alter food webs and change the dynamics of your fishery. More on that later.

Things are looking good, you've got an idea of where to set up. You like the region, you've got adequate flows, but what about the quality of the water? It's time to take some samples. The two most important measurements to get a handle of are stream temperature and dissolved oxygen. The optimal temperature range for trout varies slightly by species but you'll want to be in the 50-65° ballpark for optimizing growth and keeping fish happy. A tolerable range extends further from 40-70°, but make sure you remember to restrict fishing access if summer temperatures reach the upper tolerable range. If temperatures reach 75° you might encounter fish kills. Sites located with nearby tributaries (or water storage) can be advantageous during summer heat as fish may chase cooler water up tributaries. Similarly, if you're site is upstream from a lake, you may see fish push into a cooler stream if lakes stratify. If you install a tall bottom-release dam upstream of your site, you likely won't have to worry about stream temperatures, cold water settling at the bottom of the dam should help downstream temperatures remain stable year round.

The next most important parameter to check is dissolved oxygen. Like humans, trout breathe, but they get oxygen from water. The higher the dissolved oxygen measures in a river, the better fish can function. At a minimum, make sure dissolved oxygen stay above 6 parts per million. Also keep in mind that dissolved oxygen levels change based on elevation and temperature. High elevations have thinner atmosphere and therefore less oxygen available to dissolve in water. At the same time, higher elevations are usually cooler, and oxygen is more easily trapped in water at lower temperatures. On the other side of the thermometer, make sure to collect sampling data during the heat of summer when dissolved oxygen levels are most depleted. Aeration can replenish oxygen in water. Wind and whitewater roils create opportunities for oxygen to dissolve in water. When you get to the site design phase, rocks placed within streams can help mix oxygen into water to support trout's needs.

pH, the measure of acid vs base, is another important measurement to check. Ideal ranges for pH hover around 7, between 7-9, neither too acidic or too basic. High acidity (pH < 5) can alter trout development, kill macroinvertebrates, and are not tolerable for trout survival. Extremely low pH may indicate upstream mining or severe pollution. On the other end, trout do better in slightly alkaline systems. Here, stream productivity is elevated, supporting a rich food base, potentially growing trophy fish. But when pH exceeds 9.5, fish may become lethargic, and extreme pH (approaching 14) is lethal.

Another pH consideration. High elevations usually have slightly lower pH, believe it or not, pure rain water is slightly acidic. But brook trout seem to have a tolerance for slightly more acidity than other trout species, and may offer surprising opportunities for the perfect headwaters trout fishery.

As you travel downstream, water encounters more dissolvable elements and nutrients. You may want to measure conductivity, a test of how well water conducts a current of electricity. High conductivity could indicate many dissolved metals, like sodium, aluminum, manganese, or even heavy metals like lead, copper, zinc and mercury. The ideal range is 150 to 800 μs/cm (microsiemens/centimeter). With conductivity too high you won't be able to survey your fishery with electrofishing, which we will discuss later.

Couple that test with a hardness measurement. Hardness measures calcium and magnesium ions (which aren't as detrimental to your fishery), which will also report as part of conductivity. As previously discussed, calcium and magnesium relate to geology, and can provide advantages to organisms at various stages of a trout's food web.

If concerned about agriculture or city development arise, you may want to monitor for ammonia, nitrate, nitrite, and phosphate, common indicators of fertilizer application. But as we will see in the biological section, there are easier ways to monitor stream condition, using invertebrate species compositions instead of water quality measurements.

There are many additional or different stream chemistry tests to assess water quality and we'll leave you to go on your own deep dive.