Skykomish Draft Final Report - Wild Fish Conservancy

partitioned into upper, middle and lower thirds (Fig. 8). The latter divisions were approximated
in the field by consulting aerial photographs. The area of channel edge habitat surveyed within a
unit (A E ) was taken as the sum of the left-bank and right-bank subareas. Habitat unit interface
area (A I ) was calculated as the lower one-third of a given unit’s survey area plus the upper onethird
of the adjacent downstream unit’s survey area. Relative densities (count m -2 ) then were
calculated for (i) upper, middle and lower survey areas within units by dividing corresponding
fish counts by one-third of the total unit survey area; (ii) edge habitat areas within units by
dividing the sum of left- and right-bank fish counts by A E (i.e. two-thirds of the total unit survey
area); and (iii) habitat unit interface areas using fish counts within A I . This sampling approach
allowed testing of the hypothesis that relative fish density in habitat unit subareas with relatively
great physical heterogeneity (channel edge and habitat unit interface) exceeds that in more
homogeneous habitats (channel center and middle) (cf. Fig. 8).
For both mainstem and side channel survey areas, fish densities were calculated individually for
juveniles and adults of each species observed, and for five species categories: (1) all fish species;
(2) all salmonids (juvenile and adults); (3) adult salmonids; (4) juvenile salmonids; and (5) ESAlisted
salmonids (Chinook salmon and bull trout, adults and juveniles). For salmonid categories
2–4, mountain whitefish (Prosopium williamsoni) were excluded on the basis of the species’
relatively high abundance and unthreatened status (Snohomish River Basin Salmon Recovery
Forum, 2005).
After an initial reconnaissance snorkel of the mainstem in late July 2004, a baseline of fish use
data for summer 2004 was obtained over the course of five days (early August to early
September) by snorkeling every mapped mainstem habitat unit between rm 34.5 and rm 43.3
(units 1–74 consecutively; Figs 2–6) as well as the majority of mapped units within side channel
networks SCB (22 units) and SCC (30 units) (Tables 1, 3). In the subsequent fall 2004 survey,
mainstem habitat units were sampled by a stratified (proportional allocation) subsampling
protocol (EPA, 2002). Specifically, habitat units of different types were selected randomly for
survey in proportion to the frequency of their occurrence within two contiguous segments of the
study reach with distinct geomorphological profiles (cf. Appendix X): “Big Eddy” in Gold Bar to
Startup and Startup to the mouth of the Sultan River (Table 2). The mainstem was subsampled
using this protocol on a single day in fall 2004 (mid November). Selected units in side channel
network SCC were surveyed in winter 2004 (late December) to allow seasonal comparisons with
summer fish use data from this network. Preliminary observations on diel variation in fish
distribution and relative abundance were also made during this winter survey (cf. Table 1). WT
crews attempted to snorkel side channel network SCD and the adjacent mainstem reach (i.e.
below the mouth of the Sultan River; Skykomish rm 33–34.5) in December 2004 but extremely
poor visibility in both areas precluded the collection of fish use data. Snorkel sites and habitat
unit sample sizes for all 2004 side channel surveys are listed in Table 3.
Spawning Surveys
Washington Trout coordinated with Washington Department of Fish and Wildlife personnel to
identify the range of dates that typically encompasses the spawning runs of Chinook, chum and
coho salmon in the Skykomish River braided reach. On four days within this range during fall
2004 (between September and December; Table 1), WT field crews conducted surveys
throughout the mainstem channel and side channel networks SCA, SCB, SCC and SCD (rm 33–
43.3) to record evidence of salmon spawning activity. Surveys were performed by boat and on
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