Possible topics:
Biology
- Trout feeding behavior
- Preferred trout holding water
- Seasonal movement of trout
- How water temperature affects trout behavior
- Trout diet
- Aquatic invertebrate behavior
- Effect of pH on Trout and aquatic invertebrates
- How geology affects water chemistry
- How acid rain affects trout streams
- Differences in bedrock geology and how it affects trout streams
- How to find streams with groundwater influence
- How stream gradient affects trout
- Erosion
- How air temperature affects water temperature
- How sun affects trout behavior
- How air pressure affects fishing
- Making the most of weather forecasts
- How light behaves underwater and effects on trout vision
This list will keep me occupied for a while, but it isn't exhaustive - I'll see what else I think of as I go along.
Part I:
pH - What is it and how does it affect trout?
pH is a measure of the acidity of a sample of water. All water samples contain both hydrogen ions (H+) and hydroxide ions (OH-). When the concentrations of these two ions are equal, the water is said to be neutral and has a pH of 7. When the concentration of hydroxide ions is higher than the concentration of hydrogen ions, the pH is greater than 7 and the water is said to be basic. When the concentration of hydrogen ions is higher than the concentration of hydroxide ions, the pH is less than 7 and the water is said to be acidic.
pH affects trout in several ways:
Adult Habitat:
Adult trout can handle a fairly wide range of pH levels. Brook trout are the most tolerant of acidity, with a minimum pH of about 4.5 and a maximum of 9.5. Most natural streams have a pH between 5.5 and 8.5, so Brook trout can tolerate most streams. Brown trout are somewhat less tolerant, with a lower pH limit of 5 and an upper limit of 9.5. Rainbow trout are the least tolerant, preferring water ranging in pH from 5.5 to 9.5. Streams within a given species' pH range will provide suitable adult habitat, while those outside it will not.
Food Availability:
Aquatic invertebrates, the main food source for trout, are sensitive to pH. Freshwater crustaceans in particular can't tolerate acidic water, as the acid increases the solubility of calcium carbonate in their shells.Scuds and crayfish can be very important year-round components of trout diet, so streams containing crustaceans are usually more productive in terms of both numbers and sizes of trout.
Spawning Success:
While all adult trout species have somewhat wide pH ranges, young trout are more more sensitive. With a minimum pH of 5.0 for spawning, brook trout are again the most tolerant. Brown trout prefer a pH over 5.5, while rainbow trout will not spawn in waters above pH 6.5. In New England, where many of our streams are both naturally acidic and impacted by acid rain, brook trout are by far the most common wild trout species. Wild browns exist in some streams with higher natural pH, but are somewhat rare. Wild rainbows are especially rare, especially in southern New England, both because they have the highest minimum pH for successful spawning, and because they spawn in the spring, when pH is naturally lowest.
Why is the pH low in spring? Even in the most pristine parts of the world, rain and snow are somewhat acidic, with a typical pH of about 5.6. Add pollution into the mix and you have a serious problem. When the snowpack melts in the spring, all of that acidic precipitation is released into streams at once. Because the snowmelt typically coincides with rainbow trout spawning, eggs and/or young of the year are often killed by this spike in acidity. The only New England streams where wild rainbows are able to survive are those with a high buffering capacity, or ability to resist changes in pH.
Buffering capacity is primarily a function of geology. Carbonate ions are responsible for most of the buffering that occurs in trout streams. Limestone is probably the most common carbonate-containing rock, but there are many other types of carbonate rock, including marble and dolomite. The USGS provides bedrock geology maps for every state, so I often look up the bedrock underlying my stream of interest. If I don't know what it is, I do a Google search for "(insert rock here) buffering capacity" or "(insert rock here) acid rain", which usually turns up some information on the buffering capacity of that rock. A simpler method is just to look for rocks with "calc" or "carbonate' in the name - these rocks often have high buffering capacity.
Though it may seem complicated at first, a good understanding of pH can be beneficial to many aspects of fly fishing, including locating productive streams, determining the species likely to be present in a given stream, and selecting flies.
pH affects trout in several ways:
Adult Habitat:
Adult trout can handle a fairly wide range of pH levels. Brook trout are the most tolerant of acidity, with a minimum pH of about 4.5 and a maximum of 9.5. Most natural streams have a pH between 5.5 and 8.5, so Brook trout can tolerate most streams. Brown trout are somewhat less tolerant, with a lower pH limit of 5 and an upper limit of 9.5. Rainbow trout are the least tolerant, preferring water ranging in pH from 5.5 to 9.5. Streams within a given species' pH range will provide suitable adult habitat, while those outside it will not.
Food Availability:
Aquatic invertebrates, the main food source for trout, are sensitive to pH. Freshwater crustaceans in particular can't tolerate acidic water, as the acid increases the solubility of calcium carbonate in their shells.Scuds and crayfish can be very important year-round components of trout diet, so streams containing crustaceans are usually more productive in terms of both numbers and sizes of trout.
Spawning Success:
While all adult trout species have somewhat wide pH ranges, young trout are more more sensitive. With a minimum pH of 5.0 for spawning, brook trout are again the most tolerant. Brown trout prefer a pH over 5.5, while rainbow trout will not spawn in waters above pH 6.5. In New England, where many of our streams are both naturally acidic and impacted by acid rain, brook trout are by far the most common wild trout species. Wild browns exist in some streams with higher natural pH, but are somewhat rare. Wild rainbows are especially rare, especially in southern New England, both because they have the highest minimum pH for successful spawning, and because they spawn in the spring, when pH is naturally lowest.
Why is the pH low in spring? Even in the most pristine parts of the world, rain and snow are somewhat acidic, with a typical pH of about 5.6. Add pollution into the mix and you have a serious problem. When the snowpack melts in the spring, all of that acidic precipitation is released into streams at once. Because the snowmelt typically coincides with rainbow trout spawning, eggs and/or young of the year are often killed by this spike in acidity. The only New England streams where wild rainbows are able to survive are those with a high buffering capacity, or ability to resist changes in pH.
Buffering capacity is primarily a function of geology. Carbonate ions are responsible for most of the buffering that occurs in trout streams. Limestone is probably the most common carbonate-containing rock, but there are many other types of carbonate rock, including marble and dolomite. The USGS provides bedrock geology maps for every state, so I often look up the bedrock underlying my stream of interest. If I don't know what it is, I do a Google search for "(insert rock here) buffering capacity" or "(insert rock here) acid rain", which usually turns up some information on the buffering capacity of that rock. A simpler method is just to look for rocks with "calc" or "carbonate' in the name - these rocks often have high buffering capacity.
Though it may seem complicated at first, a good understanding of pH can be beneficial to many aspects of fly fishing, including locating productive streams, determining the species likely to be present in a given stream, and selecting flies.
No comments:
Post a Comment