PARENT SESSION
Contributed Oral Session 5: Aquatic Ecology: System Heterogeneity
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

A multiscale analysis of invertebrate drift, habitat availability, and the growth and density of brook charr (Salvelinus fontinalis).

Rader, Russell^*,1, ¹ Brigham Young University, Provo, Utah

ABSTRACT- Viewing streams as riverine landscapes comprised of a nested hierarchical mosaic of patches within patches may provide a valuable conceptual framework for stream research because understanding the effects of habitat heterogeneity from a multi-scale perspective is essential in understanding the dynamic nature of stream ecosystems. We averaged over variation at the habitat unit scale and compared drift density and brook char consumption once a week for 4 to 6 weeks in two reach types (Rosgen B and C reaches) nested in three Rocky Mountain stream segments. We also found potential explanatory processes associated with variation in brook char density and growth between reaches and stream segments, respectively. Warmer temperatures were the best explanation for differences in brook charr growth in these high mountain streams, whereas the amount of brook charr habitat in September was the only potential explanatory process associated (positively) with charr densities at the reach scale. Suitable habitat during low flows may represent a bottle-neck that determines the maximum number of adult fish that can inhabit a particular stream segment. Adult fish densities were, on average, 3.0X greater in September than July in four of the six reaches. We suggest that this pattern was caused by a decrease in flow and the movement of fish into our segments from altered habitats beyond the boundaries of this study. We found positive correlations between drift density and the average length and gradient of food-producing habitat at the reach scale. The length and/or gradient of food-producing habitat may be primary determinants of the amount of food available to downstream salmonids. The feeding efficiency of brook char (FE = drift biomass/consumption biomass) on total invertebrates at the reach scale ranged from 1.5 % to 71.9 % with a mean of 13.8 %. On average, 2.7X more invertebrate biomass was collected in the drift than was consumed by brook char at the reach scale.

Key words: multiscale analysis, drift, charr habitat, charr growth