The problem of predation
From the FishBio blog:
“Once set free in a new environment, non-native piscivores, or animals that eat fish, can wreak havoc on native fish populations. In the Colorado River Basin, such non-native piscivores are driving the Utah Division of Wildlife Resources to step up their existing predator removal program on the Green River. Recently introduced fishing laws now require anglers to kill any burbot, northern pike, smallmouth bass, or walleye caught on the Green River or any of its tributaries from Flaming Gorge Dam to the Colorado River. This push to exterminate predatory fish exists because native fishes can be extremely vulnerable to these invaders, as they often lack defenses against foreign piscivores.
In fact, over the past century, more than 40 North American fish species have gone extinct, with introduced species contributing to nearly two thirds of these losses (Miller et al. 1989). To make matters worse, many of the non-native fishes that have been purposefully stocked into Western United States waterways for sport fishing were specifically selected for their voracious predatory behavior. After more than a century of such stocking, we are discovering these aliens likely contribute significantly to the decline of native fish populations, along with other factors such as human alteration of fish habitats and river flows, and warming waters due to climate change. … ”
Continue reading at the Fish Bio blog here: The problem of predation