Biological Opinions - Bureau of Reclamation

that the proposed action incorporates elements of flow variability, real-time disease management,
and restoration activities, which can help to offset some of the adverse effects from flow
reductions.
12.4.1.2.4.1 Water Quality
Increases to water temperature in the spring may have both adverse and beneficial effects to coho
salmon juveniles. When water temperatures chronically exceed 16.5 °C, coho salmon juveniles
may become stressed (Sullivan et al. 2000, Campbell et al. 2001 in Ray et al. 2012). However,
increasing water temperature in the spring may also stimulate faster growth (Dunne et al. 2011)
and smolt outmigration (Hoar 1951, Holtby 1988, Moser et al. 1991, Clarke and Hirano 1995),
which may reduce exposure to actinospores and other pathogens in the mainstem Klamath River.
For reasons similar to those discussed for water temperature effects on coho salmon fry (i.e.,
section 12.4.1.2.3.1), when daily maximum water temperatures become chronically above 16.5
°C in May to June, the proposed action will contribute to water temperature conditions that will
be stressful to coho salmon juveniles in the mainstem Klamath River between IGD and the Scott
River (RM 143).
Low dissolved oxygen concentration can impair growth, swimming performance and avoidance
behavior (Bjornn and Reiser 1991). Davis (1975) reported effects of dissolved oxygen levels on
salmonids, indicating that at dissolved oxygen concentrations greater than 7.75 mg/L salmonids
functioned without impairment, at 6.0 mg/L onset of oxygen-related distress was evident, and at
4.25 mg/L widespread impairment is evident. At 8 mg/L, the maximum sustained swimming
performance of coho salmon decreased (Davis et al. 1963, Dahlberg et al. 1968). Low dissolved
oxygen can affect fitness and survival by increasing the likelihood of predation and decreasing
feeding activity (Carter 2005). Sublethal effects include increased stress, reduced growth, or no
growth, and are expected for coho salmon parr that are in the mainstem Klamath River below
IGD during the summer and fall.
As discussed in the Effects to Essential Habitat Types section, when the proposed action reduces
mainstem flows in the summer, NMFS expects there will likely be a reduction to dissolved
oxygen concentrations in the mainstem Klamath River between IGD (RM 190) and Orleans (RM
59). Coho salmon juveniles in the mainstem Klamath River between IGD and Orleans will be
exposed to the reduced dissolved oxygen concentrations at night and early morning when they
are not confined to thermal refugia at tributary confluences. Therefore, the proposed actions’
contributions to low dissolved oxygen concentrations in the summer will adversely affect
swimming performance (at ≤ 8.0 mg/L) and increase stress (at ≤ 6.0 mg/L) to coho salmon
juveniles in the mainstem between IGD (RM 190) and Orleans (RM 59) during this period.
12.4.1.2.4.2 Disease
Similar to the discussion on disease effects on coho salmon fry (i.e., section 12.4.1.2.3.3), when
environmental conditions are conducive to actinospore release in the spring (e.g., elevated water
temperature), the proposed action will result in hydrologic conditions in the mainstem Klamath
River that likely support high C. shasta actinospore concentrations (e.g., ≥5 spores/L actinospore
genotype II) that lead to mortality of coho salmon juveniles in the mainstem Klamath River
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