Biological Opinions - Bureau of Reclamation

In fish-bearing streams, woody debris is important for storing sediment, halting debris flows, and
decreasing downstream flood peaks, and its role as a habitat element becomes directly relevant
for Pacific salmon species (Reid 1998). Large woody debris alters the longitudinal profile and
reduces the local gradient of the channel, especially when log dams create slack pools above or
plunge pools below them, or when they are sites of sediment accumulation (Swanston 1991).
Cumulatively, the increased sediment delivery and reduced woody debris supply have led to
widespread impacts to stream habitats and salmonids. These impacts include reduced spawning
habitat quality, loss of pool habitat for adult holding and juvenile rearing, loss of velocity
refugia, and increases in the levels and duration of turbidity which reduce the ability of juvenile
fish to feed and, in some cases, may cause physical harm by abrading the gills of individual fish.
These changes in habitat have led to widespread decreases in the carrying capacity of streams
that support salmonids.
11.2.2.3 Climate Change
New information since this SONCC coho salmon ESU was listed suggests that the earth’s
climate is warming, and that this change could significantly impact ocean and freshwater habitat
conditions (Intergovernmental Panel on Climate Change 2007), which affects survival of coho
salmon. In the coming years, climate change will influence the ability to recover some salmon
species in most or all of their watersheds. Of all the Pacific salmon species, coho salmon are
likely one of the most sensitive to climate change due to their extended freshwater rearing.
Additionally, the SONCC coho salmon ESU is near the southern end of the species’ distribution
and many populations reside in degraded streams that have water temperatures near the upper
limits of thermal tolerance for coho salmon. For these reasons, climate change poses a new
threat to the viability of the SONCC coho salmon ESU. Across the entire range of the SONCC
coho salmon ESU, there are likely to be dramatic changes in the spatial structure, diversity,
abundance, and productivity. Together these changes are likely to influence the future viability
of individual populations, as well as the overall viability of the ESU.
Specific factors of a population or its habitat that could influence its vulnerability to climate
change include its reliance on snowpack, current temperature regime (how close is it to lethal
temperatures already), the extent of barriers that block access to critical habitat and refugia areas,
the range of ecological processes that are still intact, and the current life history and genetic
diversity.
Water temperature is likely to increase overall, with higher high temperatures along with higher
low temperatures in streams. A recent study in of the Rogue River basin determined that annual
average temperatures are likely to increase from 1 to 3 °F (0.5 to 1.6 °C) by around 2040, and 4
to 8 °F (2.2 to 4.4 °C) by around 2080. Summer temperatures are likely to increase dramatically
reaching 7 to 15 °F (3.8 to 8.3 °C) above baseline by 2080, while winter temperatures are likely
to increase 3 to 8°F (1.6 to 3.3 °C) (Doppelt et al. 2008). Changes in temperature throughout the
range of the SONCC coho salmon ESU are likely to be similar. The increases in temperature
within a specific stream or stream reach will depend on factors such as riparian condition,
groundwater and spring influence, the presence of upstream impoundments, and stream flow
(Bartholow 2005). Increases in winter and spring temperature regimes are likely to cause eggs to
develop more quickly, leading to early emergence. Early SONCC coho salmon fry are likely to
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