introduction of rainbow trout from hatchery stocks have resulted in cutbow hybrids that continue to diminish the genetic purity of many cutthroat trout subspecies. The introduction of hatchery-raised Yellowstone cutthroat trout into native ranges of other cutthroat trout subspecies, particularly the westslope cutthroat trout, has resulted in intraspecific breeding and diminished genetic purity of the westslope subspecies. As such, populations of genetically pure westslope cutthroat trout are very rare and localized in streams above barriers to upstream migrations by introduced species. Fisheries biologist Robert J. Behnke attributes the extinction of the yellowfin cutthroat trout and Alvord cutthroat trout subspecies to the introduction of non-native rainbow trout. Decline of the Yellowstone subspecies The population at the core of the Yellowstone cutthroat trout's native range, in Yellowstone Lake, declined significantly in the 1960s due to overharvest of mature cutthroat trout by anglers, as well as overharvesting of eggs by hatcheries in the early 20th century. Managers implemented catch and release, which required anglers to return their catches to the lake, and they terminated hatchery operations in the park, which allowed the cutthroat trout to recover. Then, in 1994, park officials discovered lake trout in Yellowstone Lake. Although lake trout were established in Shoshone, Lewis and Heart Lakes in the Snake River drainage from U.S. government stocking operations in 1890, they were never officially introduced into the Yellowstone River drainage and their presence there is probably the result of accidental or illegal introductions. By 2000, the cutthroat trout population had declined to less than 10 percent of its early 20th century abundance. However, aggressive lake trout eradication programs have killed over 1 million lake trout since 1996, and the hope is that this will lead to a restoration of cutthroat numbers. Cutthroat trout co-exist with lake trout in Heart Lake, an isolated back-country lake at the head of the Heart River that gets little angling pressure. Angling Cutthroat trout are prized as a gamefish, particularly by fly anglers. They are regulated as a gamefish in every state and province they occur in. From the Yellowstone cutthroat trout fishery in Yellowstone National Park, the unique Lahontan cutthroat trout fishery in Pyramid Lake in Nevada, and the small stream fisheries of the westslope cutthroat trout to saltwater angling for sea-run cutthroat trout on the Pacific coast, cutthroat trout are a popular quarry for trout anglers throughout their ranges. The all-tackle world record is caught in