BOZEMAN – Montana Fish, Wildlife and Parks announced Wednesday the completion of the initial data gathering for the Yellowstone River.

FWP’s fisheries staff completed its spring monitoring and preliminary analysis of the data.

The efforts focused on parts of the river that had been closed last summer after the massive fish kill.

Biologists hoped to gain a better understanding of how the event affected the trout and whitefish populations. They also want to understand what is going on with the river system and how to monitor the population in the future.

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At the time of the fish kill, the Yellowstone was experiencing low river flows and warm water temperatures for an extended period, making the conditions prime for the outbreak of the parasite Tetracapsuloides bryosalmonae (PKD).

PKD was responsible for killing at least 4,000 whitefish in the Yellowstone River in August of 2016.

Wildlife officials said numerous other factors can influence the population numbers including winter river conditions. The changes in conditions can vary depending on location and by fish species.

The section where the fish kill was the most significant was Mallard’s Rest section of the Yellowstone River. The new data supported that claim.

The observations also looked at trout populations. Data collected shows the greatest change in the stretch from the Mill Creek Bridge to the Loch Leven fishing access site.

FWP didn’t make observations of Brown Trout in the 2016 fish kill but saw a decline of about half of the larger fish and almost 30 percent Rainbow Trout population in that same size category.

On a brighter note the data showed high numbers of young trout.

FWP also reported that in the upper Yellowstone River near Corwin Springs, densities of Rainbow and Brown trout are relatively stable, like they were in years past.