Fishing for Answers

Stephanie Lynn's picture
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Post-spill data collection.

Last Thursday, the Gallatin River Task Force joined a team led by Montana Fish, Wildlife & Parks (FWP) to survey fish population on the South Fork of the West Fork (South Fork). We sampled directly above the confluence with Second Yellow Mule Creek (the drainage affected by the spill) and at three locations below the confluence. These sampling locations were chosen to provide context for the area in the absence of substantive historical data.

Gallatin River Task Force, Yellowstone Club Spill
Cutthroat checkup on the South Fork.

Data
Overall, the fish population appeared relatively healthy. Our team found five dead trout immediately downstream from the confluence with Second Yellow Mule Creek. Many sculpin showed evidence of fin erosion, related to high levels of suspended sediment carried downstream from the steep slopes exposed below the pipe failure. A thick layer of fine sediment has been deposited in the South Fork since the spill, which has the potential to impact spawning habitat. Hopefully, a good spring runoff will flush excess fine sediment through the system.

Methods
Fish population information was collected using the depletion method, described below. Warning: don’t try this at home. 

1) Assemble a team of experts.
2) Assess the stream. Select a reach at least 75 meters long or 35 times the average wetted width of the channel, whichever is longer. This ensures that all habitat types are represented.
3) String a net downstream and build barriers to fill any gaps. This will catch any missed fish that float or swim downstream.
4) Record site characteristics, including substrate composition, riparian vegetation, and stream channel and stream bank condition.
5) Set the frequency as low as possible to be effective and minimize potential injury to fish. Do not electroshock in water warmer than 62 F or during the spawn to minimize stress to fish.
6) Walk the identified reach. The shocker leads and netters follow closely, catching stunned fish as they float downstream.
7) Transfer captured fish immediately to a “live car” to minimize the risk of shocking twice. Do not overcrowd temporary holding pens.
8) Work westslope cutthroat first. Identify species, count, and measure all fish lengths. Measure all other fish species.
9) Record results.
10) Allow fish to reacclimate in “live car” or slow moving water. Release downstream and repeat.

Gallatin River Task Force, Yellowstone Club Spill
Team members shock fish for collection.

Interpretation
The good news is that the fish appear to be relatively resilient to the immediate changes in water quality; however, Fish, Wildlife & Parks will continue to analyze incoming fish population data. The Gallatin River Task Force expects laboratory results to continue rolling in throughout the week. After receiving these results, we'll release a report with analysis and historical context; we believe that the only way to accurately assess the impacts of the incident is by carefully analyzing a complete data set in the proper context.

In the words of GRTF executive director Kristin Gardner:

Water data is inherently highly variable across space (landscapes, stream reaches) and time (flow regimes, seasonal changes in temperature and light). In order to interpret watershed data collected at any given time and location, it must be put into context by comparing it to historical data (if it exists) and the time and location of the data collection. In addition, additional data should be collected in the future to characterize any changes that may have a lag time to detect.

The short and long term impacts to water quality and aquatic life cannot be determined from a single day in the field. Stay tuned for more results, analysis, and information.

Gallatin River Task Force, Yellowstone Club Spill
South Fork trout appear to have clean gill, er... bill of health, for now.


Stephanie Lynn is the education and communications coordinator for the Gallatin River Task Force. This article first appeared at gallatinrivertaskforce.org.

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