9549 - Laserfiche WebLink

Home Browse Search

In contrast to native fishes, non-native fishes generally remained abundant in the 2002 to 2004 period or increased in distribution and abundance in the study area since 1994 to 1996. Of the five non-native species for which we compared electroshing CPUE data in Lodore Canyon between the 1994 to 1996 and 2002 to 2004 periods, brown trout increased slightly and northern pike remained similar in abundance between the two periods. Similarity in brown trout abundance was somewhat surprising given the relatively warm conditions present during summer in 2002 to 2004. During summer 2002, when water temperatures were warm, brown trout were in poor condition and uncommon relative to 2003 and 2004. Brown trout apparently quickly recolonized the reach from upstream and returned to former abundance levels. White sucker, channel catfish, and smallmouth bass all increased in abundance in 2002 to 2004 compared to the 1994 to 1996 period; the latter two taxa expanded their upstream distribution as well. Size distributions of those same five non-native fish captured by electrofishing all changed in 2002 to 2004. Reasons for the bi-modal size distribution of brown trout in 2002 to 2004 were unknown, but may reflect reduced recruitment and abundance in 2002, a very warm year. More large smallmouth bass and channel catfish were found upstream, perhaps suggesting invasion from downstream rather than escapement from upstream Flaming Gorge Reservoir. Age-0 smallmouth bass were detected only in lowermost Lodore Canyon in 2002 in low numbers, the first documented reproduction there. More were noted in 2003 and 2004 and each year moved progressively upstream. Reproduction was verified by collection of very small smallmouth bass in drift net samples in 2003 and 2004, but not 2002, perhaps reflecting very low reproduction in summer 2002. Smallmouth bass reproduction continues to expand in Lodore Canyon, as an age-0 specimen was captured in autumn 2005 in uppermost Lodore Canyon. Small white suckers were also more abundant upstream, possibly indicating higher recruitment or higher reproduction there. In Lodore Canyon, red shiner and sand shiner invaded upstream reaches in 2002 to 2004 and were relatively more abundant there than in 1994 to 1996. Over all Lodore Canyon reaches, relative abundance of those two taxa increased 925 and 352% respectively, and fathead minnow 36