9716 - Laserfiche WebLink

Home Browse Search

larger (t=3.45, df=40, 2-tailed P=0.001) than the tagged individuals (81-134 mm; X=110 mm 2.04 SE; median=112 mm). Significant growth (t=22.907; df=334, 2-tailed P=0.000) was evident in the tagged individuals since their release three months (92 days) prior (Figure 7). The largest individual (134 mm) grew between 34 and 84 mm (0.37-0.91 mm/day), while the 112 mm median length tagged fish grew between 12 and 62, mm (0.13-0.67 mm/day). If the untagged individuals were actually part of the initial translocation population, then the 155 mm individual would have grown between 55-105 mm (0.60-1.14 mm/day) since its release. The ranges given above reflect that all translocated fish were between 50-100mm when moved above Chute Falls. Therefore, if we assume that the 134 mm individual was 50 mm when moved, it grew 84 mm when captured. Alternatively, if we assume it was 100 mm when moved, it would have grown only 34 mm when captured. Over five times as many speckled dace were captured during the November monitoring trip (N=13,399) than the July reconnaissance trip (N=2,293). Comparisons between their mean CPUE ± 2 SE indicated a significantly higher overall catch rate during the second trip. Rather than speckled dace being more abundant in this area, this phenomenon was more likely related to their spawning activity. Unlike the July trip, many speckled dace displayed bright breeding colors-and expressed gametes upon manual stripping during the November trip. Nets that contained some speckled dace in spawning condition typically showed the highest catch rates of both non- and spawning conditioned conspecifics (e.g., one net set captured 3,620 individuals). Speckled dace (t=4.919, df=3,299, 2-tailed P=0.000), fathead minnow (t=3.032, df=152, 2-tailed P= 0.003), and common carp (t=9.270, df=51, 2-tailed P=0.000) were significantly larger during the November trip than during the July trip. All 7 channel catfish captured in the second trip were age-0, suggesting that adults also occupied this area. DISCUSSION During the November 2003 monitoring trip, humpback chub captures above Chute Falls showed that many individuals could withstand the area's elevated CO2 levels and freshets associated with late summer-early fall months. Whether they continue to remain in this area throughout the winter and spring is unknown. Although CO2 levels at specific RKMs were relatively consistent over time during the summer months when other abiotic conditions were similar, this may not be the case in other seasons. Robinson et al. (1996) showed that in January 1992 the CO2 levels exceeded 450 mg/L above Chute Falls, which is above the 348 mg/L level where they noted stress behaviors in humpback chub. Although this may have been an isolated incident, it could also be an annual phenomenon possibly related to colder water temperatures and reduced photosynthesis. The LCR discharge is typically highest during late winter to early spring months due to the additional input from snowmelt. This may also cause a decrease in humpback chub abundance above Chute Falls. A second monitoring trip planned for late spring should reveal if these conditions are problematic to humpback chub retention within this area. 15