Relationships between Fine Sediment and Brook Trout Recruitment in Forested Headwater Streams

ABSTRACT

We examined the influence and relative importance of fine sediment on wild brook trout (Salvelinus fontinalis) populations in a forested watershed. Brook trout spawning substrate was generally comprised of 75% particles < 32 mm, with approximately 27% < 4.0 mm. Brook trout production was inversely proportional to substrate permeability in one of two years, suggesting substrate composition was influential in regulating recruitment. In that year, age-0 brook trout abundance was negatively influenced by the amount of fine sediment < 0.063 mm. We identified that for brook trout the critical fine sediment size influencing recruitment as between 0.063 and 1.0 mm. The lack of a relationship between age-0 brook trout recruitment and abundance in a second year was thought to be the consequence of severe drought causing fine sediment levels to exceed 1% < 0.063 mm in spawning substrate in all streams. Habitat variables were not related to age-0 brook trout abundance or biomass suggesting that under normal flow conditions, fine sediment was a principal determinant of juvenile trout abundance relative to other physical and biological factors.