Pflug, D., Connor, E., Hayman, B., Kassler, T., Warheit, K., McMillan, B. and Beamer, E., 2013. Ecological, Genetic and Productivity Consequences of Interactions between Hatchery and Natural-Origin Steelhead of the Skagit Watershed. Seattle City Light, Seattle, WA. pp. 207.

Puget Sound steelhead (Oncorhynchus mykiss) were listed by NOAA as Threatened under
the Endangered Species Act in May of 2007. A species listed as “threatened” is likely to become
endangered within the foreseeable future. Puget Sound steelhead are defined as a “Distinct
Population Segment” (DPS) and the ESA listing covers naturally spawned (wild born) steelhead
from river basins draining to Puget Sound, Hood Canal and the eastern half of the Strait of Juan
de Fuca. The listed steelhead include more than 50 distinct populations of summer‐ and winterrun
fish. Most steelhead are found in northern Puget Sound areas where the Skagit and
Snohomish rivers support the largest populations. Most of the hatchery stocks used in the
Puget Sound DPS area were not included in the ESA listing because they either originated
outside the DPS (Skamania summer‐run stock) or they did not represent native local populations
(Chambers Creek winter‐run stock). Hatchery stocks originating recently from local wild
broodstock steelhead were included in the listing.
It is thought that many factors collectively contribute to Puget Sound steelhead population
declines by altering survival and productivity (Hard 2007). The Puget Sound Steelhead Technical
Recovery Team (TRT) recently indentified the following factors of decline: the present or
threatened destruction, modification, or curtailment of its habitat or range; overutilization for
commercial, recreational, scientific, or educational purposes; disease or predation; the
inadequacy of existing regulatory mechanisms; and other natural or manmade factors such as
unfavorable ocean conditions and harmful hatchery practices (NMFS 2007).
Recognizing that many factors likely contribute to the decline of Skagit steelhead, this
study’s sole focus is on the potential effects of hatchery releases on natural‐origin steelhead
survival and abundance from an ecological and genetic standpoint. The findings of this report
will be an important contribution to the development of a Skagit specific recovery plan that will
address the full range of “factors of decline” and can be used by fish managers to form and
support recovery decisions.
While it is difficult to monitor escapement and survival of steelhead, current literature
suggests that significant genetic and ecological interactions occur between hatchery and
natural‐origin steelhead (Kostow et al. 2003; Mackey et al. 2001). It has been shown that even
small contributions from segregated hatchery populations to small natural populations can lead
to a significant loss of fitness (Lars Mobrand, 2005).
Kostow (2009) identified several factors capable of contributing to the ecological risks of
steelhead hatchery programs such as; large releases of hatchery fish, hatchery fish increase
density‐dependant mortality, residual hatchery fish and physical advantages of hatchery
juveniles. Other researchers have determined that hatchery steelhead can reduce survival rates
of wild (and hatchery) steelhead through four mechanisms: habitat competition, direct
predation, genetic interactions and disease.