Question

During the last century, Rocky Mountain lakes were extensively stocked with sport-fish to promote recreational fishing. What effects did these introductions have on these mountain lake ecosystems?

Answer 1

Stocking Rocky Mountain lakes with non-native sport-fish has led to significant ecosystem changes, including the decline of native fish populations due to predation by introduced top predators and habitat alterations. Unauthorized introductions have generated environmental and economic issues. The overall biodiversity of these ecosystems has been compromised due to these stocking practices.

Step-by-step explanation:

The stocking of Rocky Mountain lakes with non-native sport-fish has had significant effects on these ecosystems. Initially, the purpose of stocking was to supplement declining native faunas and to provide sport and food for a growing population. However, unauthorized stockings have now become the major source of fish introductions. Such illegal activities interfere with water body management, creating environmental and economic impacts. For example, illegal introductions have necessitated the expenditure of millions to manage non-native species like the Northern Pike in Lake Davis, California.

Many of these introduced sport-fish are top predators. Predatory fishes such as brown trout and striped bass have been stocked even without understanding their initial impacts. These predatory species often replace native fishes, leading to reduced biodiversity and altered ecosystem dynamics. For instance, the introduced redeye bass in California streams managed to eliminate 4-5 native fish species through predation and habitat occupation.

In the case of reservoirs, which are frequently stocked as they are near population centers, the environmental effects include changes in water temperature, chemistry, and flow, among others, which in turn affect the natural habitats of native species. The native fish populations have been seen to decline following the introduction of non-native predators, which directly link to the increase in non-native fish richness. The altered habitats facilitate the invasion of non-natives, showing that the dynamics of these ecosystems have been significantly altered by stocking practices.