The Effects of Yellowstone’s Declining Trout Population

The devastating effects of Yellowstone’s cutthroat trout decline have far reaching impacts. Scientists are linking grizzly bears’ diet changes, once primary trout, to them scourging the countryside for a meal, which has resulted in them turning to an elk calf diet. In fact, scientists question whether the two remain linked, as fewer elk herds are migrating outside the park’s boundaries.

Yellowstone National Park was recently the subject of two studies, which confirmed scientists’ link between the declining trout population and the number of elk calf deaths. Scientists admitted they were shocked by the studies’ findings, which has ultimately resulted in an elk calf population decrease in the neighborhood of four- to 16-percent. In reality, this has decreased migratory elk herds by approximately two- to 11-percent.

Others cite evidence that Yellowstone’s ecosystem is very delicate and the grizzly bear seems to be at the heart of it. In fact, grizzlies are often viewed as the “consummate connector” in this region. In fact, David Mattson, a U.S. Geological Survey Wildlife Biologist, made the statement: “We’re watching probably the first state of impoverishment in the ecosystem as far as grizzly bears are concerned.”

Another study, conducted by Jennifer Fortin of Washington State University, highlighted findings that showed a decrease of 70- to 95-percent in grizzly bears’ trout consumption between 1997 and 2009. Additionally, this study analyzed the fecal matter from droppings, which showed that grizzly bears consumed one elk calf for every two- to four-day interval and black bears every four to eight days.

Yellowstone offers a plethora of statistical data, which has helped scientists make links between the trout and elk calf declines. Yellowstone has documented studies showing that cutthroat trout has declined by as much as 90-percent since the invasive lake trout predator was illegally introduced to the area. Yellowstone also has fairly accurate statistical data for elk cow-to-calf ratios, including migratory elk herds.

To make matters worse, consider the data from a study on nearby Clear Creek, one of the many tributaries that flow into Yellowstone Lake. In 1988, Clear Creek saw 54,000 cutthroat trout. In 2007, that number was a mere 500. Astounding, right? But when analyzing the elk population that has been declining since 1988, which recorded 19,000 elk, 2012 saw a mere 3,900 elk in the park. While 80-percent of elk become pregnant, only 10-percent still had their calves by the summertime months.

With grizzly bears being one of 28 species that depend primarily on cutthroat throat, the ecological consequences of this decrease could have a potentially devastating impact on our delicate ecosystem and the animal kingdom.


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