Brown Trout - Conservation Status

Conservation Status

The fish is not considered to be endangered, although, in some cases, individual stocks are under various degrees of stress mainly through habitat degradation, overharvest and artificial propagation leading to introgression. Increased frequency of excessively warm water temperatures in high summer causes a reduction in dissolved oxygen levels which can cause 'summer kills' of local populations if temperatures remain high for sufficient duration and deeper/cooler or fast, turbulent more oxygenated water is not accessible to the fish. This phenomenon can be further exacerbated by eutrophication of rivers due to pollution - often from the use of agricultural fertilizers within the drainage basin.

Overfishing is a problem where anglers fail to identify and return mature female fish into the lake or stream. Each large female removed can result in thousands fewer eggs released back into the system when the remaining fish spawn.

Another threat is other introduced organisms. For example in Canada's Bow River, a non-native alga Didymosphenia geminata - common name rock snot (due to appearance) - has resulted in reduced circulation of water amongst the substrate of the river bed in affected areas. This, in turn, can greatly reduce the number of trout eggs which survive to hatch. Over time, this leads to reduction of the population of adult fish in the areas affected by the algae, forming a circle of decline. Rock snot is believed to have spread accidentally on the soles of the footwear of visitors from areas where the alga is native. The wide variety of issues that adversely affect brown trout throughout its range do not exclusively affect brown trout, but affect many or all species within a water body, thus altering the ecosystem in which the trout reside.

In small streams, brown trout are important predators of macroinvertebrates, and declining brown trout populations in these specific areas would affect the entire aquatic food web. S. trutta morpha fario prefers cold (though in comparison with other "trout", this species has a somewhat higher temperature preference of about 60-65°F, or 15.5-18.3°C), and well-oxygenated upland waters, especially large streams in mountainous areas.

Cover or structure is important to trout, and they are more likely to be found near submerged rocks, undercut banks, and overhanging vegetation. Structure provides protection from predators, bright sunlight, and associated high water temperatures. Access to deep water for protection in winter freezes, or fast water for protection from low oxygen levels in summer are also ideal.