Effects of substrate composition on apache trout fry emergence

Abstract

Artificial substrates were used under laboratory conditions to assess the potential effects of fine sediment (< 2 mm) on a native southwestern (USA) salmonid. Apache trout (Oncorhynchus apache). Asynchronous, complementary field assessment of stream substrate composition was made in the White Mountains of east-central Arizona, the native range of Apache trout. Laboratory studies suggested that fry emergence was significantly reduced at 25% or greater by weight of fine sediments. Mean fine content of substrates in streams in the White Mountains ranged from 8 to 43% and averaged about 24%. Based on laboratory and field data, streams in the White Mountains region are approaching the threshold that could dramatically limit reproductive success of Apache trout. Further, a significantly greater content of optimum spawning substrate (8–32 mm) was estimated in streams emanating from the Fort Apache Indian Reservation than those in Apache Sitgreaves National Forest. © 2001, Copyright Taylor & Francis Group, LLC.