Title

Changes in Perlidae Populations on the South Fork of the Flathead River 5 Years after Installation of a Selective Withdrawal System on Hungry Horse Dam

Abstract

A selective withdrawal system was added to Hungry Horse Dam in 1994 to help downstream fish populations. To evaluate the effects of that system on perlid stoneflies of the South Fork, I replicated a study of the South Fork, Middle Fork, and Main Stem of the Flathead done before the installation of the system. I sampled in July, August, and October 1999 and in early and late March 2000. The system appeared to warm the South Fork waters significantly in late summer months by as much as 5oC. The temperature of the South Fork in 1999 was warmer than the temperatures of the Middle Fork and Main Stem. The numbers of Hesoperoperla pacifica and Claasenia sabulosa appeared to be lower than 1994 in all streams. No Perlidae were identified on the South Fork in August of 1999.

Start Date

14-4-2000 12:00 AM

End Date

14-4-2000 12:00 AM

Document Type

Poster

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Apr 14th, 12:00 AM Apr 14th, 12:00 AM

Changes in Perlidae Populations on the South Fork of the Flathead River 5 Years after Installation of a Selective Withdrawal System on Hungry Horse Dam

A selective withdrawal system was added to Hungry Horse Dam in 1994 to help downstream fish populations. To evaluate the effects of that system on perlid stoneflies of the South Fork, I replicated a study of the South Fork, Middle Fork, and Main Stem of the Flathead done before the installation of the system. I sampled in July, August, and October 1999 and in early and late March 2000. The system appeared to warm the South Fork waters significantly in late summer months by as much as 5oC. The temperature of the South Fork in 1999 was warmer than the temperatures of the Middle Fork and Main Stem. The numbers of Hesoperoperla pacifica and Claasenia sabulosa appeared to be lower than 1994 in all streams. No Perlidae were identified on the South Fork in August of 1999.