Yellowstone Lake was one of the last remaining sanctuaries for genetically pure Yellowstone cutthroat trout, a species native to the pristine streams and waterways of the Greater Yellowstone Ecosystem. But its numbers are diminishing quickly, due mainly to hybridization with rainbow trout and the introduction of brown and brook trout that have overtaken cutthroat habitat, feeding and spawning grounds in rivers like the Yellowstone, Madison and Gardner. Lake trout are expected to do the same, but in this case, they eat cutthroats at the same time they bully them out of their neighborhood. As for the other critters that live around the lake's 110 miles of shoreline, reduced cutthroat numbers makes the task of finding food a little more difficult. Each spring, grizzly and black bears flock to the streams that empty into the lake to snag spawning cutthroats.
Fewer fish means a longer buffet line and tougher competition among bears.
Grizzlies and bald eagles are threatened species, and biologists cringe at the thought or anything threatening their livelihood. Fewer cutthroats could also impact osprey and otters. So that is why it is open season on the lake trout. Park rangers require anglers to keep the lake trout they catch. There is no limit on them, but rangers do ask that fisherman report their catch so biologists can better track behavior and population size.