Beamer, E., Henderson, R. and Wolf, K., 2004. Bull Trout Use of Swinomish Reservation Waters. Skagit River System Cooperative, La Conner, WA. pp. 10.

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This report describes how bull trout use Swinomish Reservation waters based on existing
data collected by the Skagit River System Cooperative (SRSC) Research Program. The
same general relationships between fish and habitat use and Skagit Bay bull trout
population trends have been provided as a draft report (Beamer and Henderson 2004) to
the Puget Sound Bull Trout Technical Recovery Team (TRT) via Fred Goetz of the TRT
and United States Army Corps of Engineers (USACOE).
Current bull trout population size within the Swinomish Reservation waters has increased
4-fold since 1995. Age structure of bull trout in Skagit Bay has also become older and
more complex. From 1996 through 1998, 95% of the population was sub-adult sized, and
too young to reproduce. From 1999 through 2003, a tri-modal length distribution of fish
indicates sub-adult, first year spawner, and mature spawner sized fish are present.
Together, these population factors (more abundance and multiple age classes) should
make the current Skagit Bay bull trout population more resilient to threats to its
population than a decade ago. Since we are also investigating habitat use by bull trout
during a time where more individual bull trout are present, we are more likely to be
detecting true habitat preferences by bull trout rather than making random observations of
presence or absence.
We describe bull trout use for four habitat areas found within the Swinomish Reservation.
They are: freshwater streams (Figure 1), lagoon or saltmarsh dominated “pocket”
estuaries (Figure 2), shoreline areas in Skagit Bay (also Figure 2), and historic delta areas
within and along Swinomish Channel (Figure 3). We also describe the potential
importance of habitat in terms of its direct or indirect use by bull trout. Direct use refers
to the idea that bull trout are present in a specific habitat area performing a necessary life
cycle function such as spawning, rearing/foraging, or seeking refuge (e.g., from predation
and/or environmental stressors). Indirect use refers to habitats that support food-web
elements/organisms upon which bull trout depend. Indirect use conclusions are
established by observing abundant prey resources (known to be regionally consumed by
anadromous bull trout) within specific habitat types.

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