Summary of the possible consequences to fish of beaver activities
Positive effects
Habitat is created for larger fish, providing angling opportunities (salmonids in cold water streams, centrarchids and some esocids in warm water streams).
The debris cover provided by the lodge and the food cache can attract some fish species (e.g., salmonids, percids, centrarchids).
Hydrological effects are stabilised, so that bed scouring and bank erosion are decreased. More stable stream flows are beneficial to invertebrate and fish production.
Water temperature stabilisation and warming could increase production in cold water streams.
In streams with high sediment loads, sediment will be trapped in the impoundment.
Coarse, particulate and dissolved organic matter is increased in the pond, providing food for invertebrates, through fungal and microbial pathways.
Nutrients may be generated (N, P), increasing he fertility of the pond and downstream stretches.
Acidity may be reduced, and Al may be immobilised.
The dam collects organic detritus, and provides a substrate for lotic type invertebrates, providing food for fish downstream.
Refugia can be provided in the pond at certain times.
Negative effects
Upstream migration may be impeded (larger dams; dams above culverts which were partial barriers).
Warming of water temperatures may be detrimental in some marginal habitats for cold water fish.
Spawning sites may be inundated and silted.
The fish composition and interactions may change, so that less desired species for angling predominate.
Habitat may be created for avian, mammalian or piscine predators, with negative effects on desired fish species.
