Putting the bull in climate change threats to bull trout

According to an article at the Missoulian, bull trout are under seige in Montana due to climate change:

Bull trout are listed as a threatened species under the federal Endangered Species Act, and their fate has a big impact on land use, fishing opportunities and public policy throughout northwest Montana ...

Bull trout face several threats to their survival. On the spawning end, they need clean, clear creeks in which to lay eggs. Those can be damaged by silt from old road culverts or dry up from declining snowpacks due to climate change.

The USDA National Water and Climate Center maintains a database of historical snowpack data for Montana.  There are 160 stations with effectively complete end-/first-of-month snowpack records over the past 30 years.  In the environmental sciences, we commonly consider trends in snowpack for the end/start of February/March, March/April, and April/May when assessing potential impacts on streamflow later in the season.

This makes for a total of 480 month-station snowpack trend combinations to consider in Montana.

Of the 160 snowpack monitoring stations throughout the state, only 4 stations had at least one month with a significant declining trend in snowpack (measured as snow water equivalent) over the last three decades, while 14 stations had significant increasing trends in snowpack during this time.  The remaining 142 stations had no significant trend, and many – if not most – correlations were toward increasing snowpack.

Only 9 of the 480 month-station combinations had significant declining trends in snowpack, compared to 20 with significant increasing trends.  Once again, the remainder of the month-station combinations exhibited no significant snowpack trends, and the overall correlation was likely toward higher – rather than lower – snowpacks.

Overall, there appears to be no evidence that snowpacks in Montana have been declining in recent decades.  This is clearly a fact that needed to be stated in the Missoulian's article.  There may be a number of pressures on bull trout populations, but reduced snowpacks over the past 30 years due to climate change does not appear to be one of them.

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