Beamer, E. and Henderson, R., 2004. Distribution, abundance, timing, and size of anadromous bull trout in the Skagit estuary. Skagit River System Cooperative, La Conner, WA. pp. 21.

We have conducted bi-weekly fish sampling in habitat potentially utilized by anadromous
bull trout in the Skagit estuary annually since 1995. We used beach seine and fyke traps
depending on the habitat types from February through August (delta) or February through
October (Skagit Bay). We sampled year round in 2003.
Bull trout use delta blind tidal channels, but may not directly use smaller and shallower
channels, or channels more distant from river distributaries. There was no annual increasing
or decreasing trend in abundance. There is significant annual variation in timing, but the
peak is usually in June while the primary period of presence runs from April through
August.
Bull trout are also present in Skagit Bay. However, presence in shallow intertidal habitat was
very low compared to the deeper intertidal-subtidal fringe. Bull trout are present in the
deeper intertidal-subtidal habitats year round. Peak abundance occurs in May or June. In
recent years, we observed a bi-modal distribution with the second peak during fall months.
Bull trout abundance from February through October in Skagit Bay increased four-fold from
1995 through 2001. The bull trout population in Skagit Bay has also increased in length
frequency complexity over the sampling period. From 1996 through 1998, 95% of the
population was sub-adult sized, and too young to reproduce. From 1999 through 2003, a trimodal
length distribution is evident that includes sub-adult, first year spawner, and mature
spawner sized fish.