Warming rivers ward off fishers

by grahamhendrix on November 17, 2015 - 3:18pm

An interesting point of view to the detrimental impacts of climate change is presented in Brett French’s article in the Billings Gazette. He demonstrates how warming temperatures, low precipitation, and reduced spring melts are wreaking havoc on the Yellowstone cutthroat trout. This species is adapted to cold streams, but as the water warms it’s being outcompeted by more common species like smallmouth bass, as well as rainbow and brown trout, migrating upstream from warmer bodies of water. The latter two are particularly concerning because they can inarterbreed with the Yellowstone cutthroat, raising concerns about maintaining the genetic purity of this species. Government wildlife officials are apparently considering the construction of barriers to prevent the further migration of these invasive species.

Above and beyond the potential biodiversity loss, the economic consequences of climate change in this system are also presented. Outdoor recreation in Montana, much of which is dependent on sport fishing, generates $1.5 billion in wages and is responsible for 64 thousand jobs. The reduced abundance of some fish species is compounded by reduced flow and increased water temperature in some rivers; when temperature surpass a certain threshold, the river is closed to fishing, so that human pressure is focussed on the few remaining open streams. Lower spring melts from a lack of glaciers (there were 150 glaciers in the region in 1850, now only 25 remain - and projections are for all to have disappeared by 2030) are also detrimental to the wetlands in the area, which are prime habitat for waterfowl throughout the continent.

This article does a good job of presenting the many nuanced sides to this issue: it’s not a clean-cut example of “this is a problem, this is what it’s causing, and this is how to solve it.” It effectively demonstrates how climate change is a wicked problem with far reaching impacts: there is no simple correct solution to  the problem, and there are many interested stakeholders. Some of these stakeholders, like the wilderness guides discussed in this article, do not necessarily have clear opinions themselves about the best course of action: although they are aware that climate change is causing severe problems for their livelihood, they still disagree about responsibility and potential solutions. There are also several feedback loops at play: increasing air temperatures not only warm the stream water directly, but also prevent the accumulation of snow at higher elevations, restricting the ability of spring melt to lower the stream’s temperature.

Uncertainty is also playing a key role in compounding the problem, because the overall effects being observed (warmer water, less snow melt, less precipitation) are not consistent: there is high year-to-year variation, so that predicting the circumstances in an upcoming year and trying to plan accordingly is a very difficult task.

There are elements of command-and-control management in this system. The construction of barriers in the streams to hold back the rainbow and brown trout would be an example of this, as would be the closure of streams during hot periods. These techniques have good motives, but they might not prove as effective as managers hope. The inherent uncertainty in the system means that these actions may create perverse outcomes: if closure of particularly hot waterways leads to more fishers on the other open streams, the increased pressure on these few routes could have severe impacts on the trout population.