Habitat is key. It is the most important factor affecting wild trout distribution and abundance.
Water temperature is single most important factor limiting wild trout. Trout need cold water to survive. Cooler water temperature allows water to hold more oxygen.
Forested areas along streams and rivers (known as "riparian areas") provide shade and help to cool the water. These naturally vegetated areas also prevent erosion, filter pollutants, and provide shelter and food for fish and other aquatic organisms. Protecting and enhancing forested riparian areas is critical to maintaining the conditions trout require to thrive. The future effects of climate change will heighten this need.
Good habitat is:
- Diverse – riffles, pools, variety of depths, velocities and substrates. Trout species and lifestages differ in habitat requirements. A diversity of habitats is required to meet these needs.
- Complex – interactions of natural streamflows and adjacent lands exists. Forested riparian areas provide:
- stable streambanks
- large wood recruitment to stream channel that creates complex habitats for fish and other aquatic life
- organic matter recruitment that is a source of food/energy in stream systems
- retention and filtration of run-off from farms and other nutrients, sediment and other pollutants before reaching surface waters
- Messy – boulders, fallen trees and organic matter are all part of good habitat. Uniform channels with neatly manicured lawns to the edge may be attractive to some, but is poor trout habitat.
- Connected – just as we need to move through the road network to meet our life needs, wild trout and other aquatic populations need to move through the stream networks.
- Wild trout move daily to feeding and resting habitats, and move seasonally or in response to changing environmental conditions (temperature, flow) or lifestage requirements (spawning, smolting).
- Dams and thousands of impassable culverts within Vermont's stream network are barriers to trout movement.
Unaltered rivers and streams moderate water flow through natural hydrology and fish can adjust to changing conditions. Man-made changes in water flow can limit wild trout production by increasing the magnitude and duration of extreme conditions, such as floods or drought. For example, hydroelectric operations and water withdrawals can impact trout by manipulating the natural hydrology.