A study in America suggested that the catch rate of trophy-sized trout (longer than 38 cm) was 28 times greater in the catch-and-release area than in a harvest (catch and kill) area.
Barriers like weirs, culverts and hatches can prevent resident brown trout from accessing spawning areas and habitat vital to all other stages of their lifecycle.
Brown trout caught on fly are less likely to die after release than trout caught on bait.
Calcium carbonate precipitation is a phenomenon that occurs in chalk streams and causes the river bed to become cemented by deposits of calcium carbonate or ‘tufa’. This causes spawning gravels to concrete over and prevents fish from digging reds. This problem is caused by low and slow river flows and increased inputs of nitrogen.
Catch and release is an important management tool that prevents over exploitation of fragile wild brown trout fisheries. ’’…a good game fish is too valuable to be caught only once.’’ – Lee Wulf.
Conifers can capture acidic emissions on their needles, rain washes this off and the acidified water then acts on the soil to release heavy metal ions poisonous to salmonoid through uptake via their gills.
Excessive angling pressure can reduce the abundance of trout populations by selectively removing large, reproductively active specimens from the population.
Experimental studies of stocked and wild brown trout in natural conditions demonstrate that farm reared fish have poor survival and reproduction compared to wild fish (often less than 10%).
Farmed trout are selectively bred for different characteristics to wild fish: for example, they spawn earlier and put on weight faster. Farmed trout are heavily domesticated, one result being that they have a reduced reaction to predation, making them more vulnerable than wild fish to predators (including anglers!).
Hybrid wild/farmed fish are weaker than their wild counterparts, thus stocking can, over time, reduce the health, reproductive potential and ultimately numbers of trout in a river system.
Introduced organisms can adversely impact wild trout, For example in Canada & New Zealand, 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 which in turns reduces the number of trout eggs which survive to hatch.
Juvenile trout survival and abundance in southern chalk streams is strongly correlated to river flow in the preceding April (Solomon and Paterson,1980), which suggests that April flow is critical for trout production and requires protection.
Many strains of domesticated trout have been in captivity for 30+ generations.
Overgrazing by livestock has long been considered damaging to wild salmonoid populations as it can remove river bank plant cover and in certain cases accelerate bank erosion leading to wider and shallower river channels with decreased current speeds and increased sediment loads. However, controlled livestock grazing might be really good for promoting biodiversity along a river and controlling invasive plant species such as Himalayan balsam.
Sea trout conservation is affected by what goes on at sea as well as in spawning tributaries. The overfishing of sand eels in the North Sea is likely to affect the numbers of sea trout returning to their home rivers.
Stocked brown trout are blamed for threatening the genetic integrity of both Balkan and Mediterranean native trout strains.
Studies in Europe have demonstrated that on small watercourses, hydropower schemes can devastate wild trout populations.
Studies of trout populations in Europe and N. America show that stocking can lead to the loss of natural genetic diversity, potentially affecting their ability to adapt and survive in the future.
The Balkans in Europe is a Centre of endemism (uniqueness) for brown trout. In this region, four sub-species, distinct in both appearance and habits can be found; these include the Ohrid Trout, Marble Trout, Soft mouth Trout and Dentex Trout.
The more fish that are stocked into a water body, the slower they will grow in the wild.
The simplest way to tell a farmed fish from a wild fish is to look at the condition of their fins. Many stocked fish suffer from damage to their fins (often healed, leaving them kinked or rounded). However, wild fish can also suffer from abraded fins and tails after spawning.
Trout and salmon are especially vulnerable to climate change and global warming because they are dependent on an abundance of clear, cold water. As cold water habitats warm, rising temperatures will have negative impacts on a variety of life history phases—from eggs to juveniles to adults.
Using barb less hooks can reduce the time taken to remove a hook when releasing trout and therefore limit damage to the fishes mouth.
Very acidic water – pH 3.5 – can cause S. trutta eggs to die within ten days