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We conducted laboratory experiments to determine the sprint swimming performance of wild juvenile and adult bull trout Salvelinus confluentus. Sprint swimming speeds were estimated using high-speed digital video analysis. Thirty two bull trout were tested in sizes ranging from about 10 to 31 cm. Of these, 14 fish showed at least one motivated, vigorous sprint. When plotted as a function of time, velocity of fish increased rapidly with the relation linear or slightly curvilinear. Their maximum velocity, or Vmax, ranged from 1.3 to 2.3 m/s, was usually achieved within 0.8 to 1.0 s, and was independent of fish size. Distances covered during these sprints ranged from 1.4 to 2.4 m. Our estimates of the sprint swimming performance are the first reported for this species and may be useful for producing or modifying fish passage structures that allow safe and effective passage of fish without overly exhausting them.
We examined the degree to which bird community composition is associated with livestock grazing in the Cascade-Siskiyou National Monument in southern Oregon. We sampled riparian and adjacent upland areas along routes within mixed-conifer forests and oak woodlands. For each route, we generated a continuous measure (0–100%) of livestock grazing utilization and used this measure to group routes into low (0% to 40%) and high (>40%) grazing utilization classes. In 2003 and 2004, we conducted point counts along each route to quantify avian species richness and community composition. In mixed-conifer forest, species richness was significantly greater in upland areas and in areas with high grazing utilization; however, bird community composition differed only between upland and riparian areas and not between areas of low and high grazing utilization. In oak woodlands, bird community composition was significantly different between high and low utilization, but not between riparian and upland areas. Bird communities associated with high grazing utilization had significantly fewer shrub-nesting, foliage-gleaning, and long-distance migrant species than those associated with low grazing utilization. Our results suggest that grazing influences bird community composition in both riparian and upland areas of oak woodland vegetation. Reducing grazing in oak woodlands would likely lead to increases in the relative abundance of long-distance migrants, foliage gleaners, and shrub-nesting species in this habitat.
We studied the relationships between autotrophic and heterotrophic microbiota and metalimnetic oxygen and ammonium maxima that develop during the summer in Lake Whatcom, Washington (USA). A metalimnetic oxygen maximum was present from mid-July through mid-August at Site 1, the most eutrophic of the lake's three basins, coinciding with high metalimnetic chlorophyll concentrations and peak densities of cyanobacteria and diatoms. The oxygen maxima were located approximately 2 m higher in the metalimnion than the chlorophyll maximum. After mid-August, peak algal densities shifted to the epilimnion and the oxygen maximum disappeared. A metalimnetic ammonium maximum was present at Site 4, the most oligotrophic basin, throughout the summer, coinciding with high counts for metabolically active bacteria. The ammonium maxima appeared to be caused by an excess rate of aerobic decomposition of organic matter raining from the photic zone compared to the rate of nitrification. The ammonium maxima were somewhat linked to the location of the chlorophyll maxima.
We used observational and experimental approaches to obtain information on factors affecting the timing of maturation of kokanee Oncorhynchus nerka, a semelparous, landlocked salmon. Gonadal staging criteria were developed and applied to three kokanee populations in Idaho lakes and reservoirs. Testes were classified into three stages: immature (stage one, S1), maturing (S2), and mature (S3). Ovaries were classified into eight stages: immature (S1–S3), transitional (stage S4), maturing (S5–S7), and mature (S8). Males entered the maturing stage (S2) in February through April of the spawning year. Females entered maturing stage (S5) as early as July of the year before the spawning year, and as late as March of the spawning year. Three hatchery experiments demonstrated that attainment of a larger body size 10 to 16 months before spawning increased the likelihood of initiation of maturation in both sexes. No gonads in a state of regression were observed. A gonadosomatic index above 0.1 by early July was a good indicator of a maturing male, and a gonadosomatic index above 1.0 by early July was a good indicator of a maturing female. Instantaneous growth rates were not good predictors of maturation, but attaining a size threshold of 18 to 19 cm in the fall was a good predictor of maturation the following year. This improved knowledge of kokanee maturation will permit more effectively management of the species for age, growth and size at maturity as well as for contributions to fisheries.
Number and location of canopy strata have been key forest structure variables that guide the management of wildlife habitat, timber production, and fire hazard. Forest canopy stratification algorithms Forest Vegetation Simulator (FVS), Landscape Management Systems (LMS), Vertical Tree Stratification Program (TSTRAT), and Mid Crown Line (MIDCL) reported different numbers and locations for canopy strata in artificial stands where these strata parameters were known. Number and location of strata identified by algorithms varied in unmanaged fir-pine stands as well. LMS failed to identify well-populated stratum and reported stratum in a continuum of tree heights. The TSTRAT algorithm truncated lower stratum bounds causing numerous strata to be identified regardless of foliage discontinuities. FVS failed to identify strata in the upper canopy of tall stands or when transition trees were present between strata. MIDCL results closely agreed with the tree list standard in artificial stands and the number of age cohorts in unmanaged stands. The fixed 50% crown line threshold in MIDCL reduced MIDCL stratification capability in crown ratios over 60%. Existing forest structure classifications based on canopy strata assume a close relationship between strata and age cohorts. The more accurate linkage between strata and age cohorts in MIDCL may improve classification efforts. An add-on process in MIDCL checked for discontinuities in lower crown base height and layering within individual strata; together they described canopy strata and porosity and may enhance the linkage between canopy structure and wildlife habitat.
Analysis of key components of the alpine North Cascade hydrologic system indicate significant changes in glacier mass balance, terminus behavior, alpine snowpack, and alpine streamflow from 1950 to 2005. North Cascade glacier retreat is rapid and ubiquitous. All 47 monitored glaciers are currently undergoing a significant retreat and four of them have disappeared. Annual mass balance measured on ten glaciers, averaging 30–50 m in thickness, yields a mean cumulative annual balance for the 1984–2006 period of −12.4 m water equivalent (m we), a net loss of 14 m in glacier thickness and 20–40% loss of their total volume in two decades.
The data indicate broad regional continuity in North Cascades glacial response to climate. The substantial negative annual balances have accompanied significant thinning in the accumulation zone of 75% of North Cascade glaciers monitored. This is indicative of glacier disequilibrium; a glacier in disequilibrium will not survive the current warmer climate trend. Alpine snowpack snow water equivalent (SWE) on April 1 has declined 25% since 1946 at five USDA Snow Course sites. This decline has occurred in spite of a slight increase in winter precipitation. The combination of a decline in winter snowpack and a 0.6° increase in ablation season temperature, during the 1946–2005 period in the North Cascades, has altered alpine streamflow in six North Cascade basins. Observed changes in streamflow are: increased winter streamflow, slightly declining spring streamflow and a 27% decline in summer streamflow. Only in the heavily glaciated Thunder Creek Basin (> 10% glaciated) has summer streamflow declined less than 10%; this is attributable to enhanced glacier melting.