Protocol for determining bull trout presence

The Western Division of the American Fisheries Society was requested to develop protocols for
determining presence/absence and potential habitat suitability for bull trout. The general
approach adopted is similar to the process for the marbled murrelet, whereby interim guidelines
are initially used, and the protocols are subsequently refined as data are collected. Current data
were considered inadequate to precisely identify suitable habitat but could be useful in stratifying
sampling units for presence/absence surveys. The presence/absence protocol builds on previous
approaches (Hillman and Platts 1993; Bonar et al. 1997), except it uses the variation in observed
bull trout densities instead of a minimum threshold density and adjusts for measured differences
in sampling efficiency due to gear types and habitat characteristics. The protocol consists of: 1.
recommended sample sizes with 80% and 95% detection probabilities for juvenile and resident
adult bull trout for day and night snorkeling and electrofishing adjusted for varying habitat
characteristics for 50m and 100m sampling units, 2. sampling design considerations, including
possible habitat characteristics for stratification, 3. habitat variables to be measured in the
sampling units, and 3. guidelines for training sampling crews. Criteria for habitat strata consist
of coarse, watershed-scale characteristics (e.g., mean annual air temperature) and fine-scale,
reach and habitat-specific features (e.g., water temperature, channel width). The protocols will be
revised in the future using data from ongoing presence/absence surveys, additional research on
sampling efficiencies, and development of models of habitat/species occurrence.