Biological Opinions - Bureau of Reclamation

water temperatures up to 19 ºC in the Klamath River (Strange 2008). Coho salmon spawning
within the Klamath River basin usually commences within a few weeks after arrival at the
spawning grounds (NRC 2004) between November and January (Leidy and Leidy 1984).
Coho salmon spawning has been documented in low numbers and as early as November 15
within the mainstem Klamath River. From 2001 to 2005, Magneson and Gough (2006)
documented a total of 38 coho salmon redds between IGD (RM 190) and the Indian Creek
confluence (RM 109), although over two-thirds of the redds were found within 12 river miles of
the dam. Many of these fish likely originated from the IGH. The amount of mainstem spawning
habitat downstream of IGD has been reduced since construction of the dam because, for one
thing, the introduction of spawning gravel from upstream sources has been interrupted.
12.3.1.2 Egg Incubation and Fry Emergence
Coho salmon eggs typically hatch within 8 to 12 weeks following fertilization, although colder
water temperatures likely lengthen the process (Bjornn and Reiser 1991). Upon hatching, coho
salmon alevin (newly hatched fish with yolk sac attached) remain within redds for another 4 to
10 weeks, further developing while subsisting off their yolk sac. Once most of the yolk sac is
absorbed, the 30 to 35 millimeter fish (then termed “fry”) begin emerging from the gravel in
search of shallow stream margins for foraging and safety (NRC 2004). Within the Klamath
River, fry begin emerging in mid-February and continue through mid-May (Leidy and Leidy
1984).
12.3.1.3 Juvenile Rearing
12.3.1.3.1 Fry
After emergence from spawning gravels within the mainstem Klamath River, or as they move
from their natal streams into the river, coho salmon fry distribute themselves upstream and
downstream while seeking favorable rearing habitat (Sandercock 1991). Further redistribution
occurs following the first fall rain freshets as fish seek stream areas conducive to surviving high
winter flows (Ackerman and Cramer 2006). They do not persist for long periods of time at water
temperatures from 22 ºC to 25 ºC (Moyle 2002 and references therein) unless they have access to
thermal refugia. Lethal temperatures range from 24 to 30 ºC (McCullough 1999), but coho
salmon fry can survive at high daily maximum temperatures if (1) high quality food is abundant,
(2) thermal refugia are available, and (3) competitors or predators are few (NRC 2004). Large
woody debris and other instream cover are heavily utilized by coho salmon fry (Nielsen 1992,
Hardy et al. 2006), indicating the importance for access to cover in coho salmon rearing.
12.3.1.3.2 Parr
As coho salmon fry grow larger (50-60 mm) they transform physically (developing vertical dark
bands or “parr marks”), and behaviorally begin partitioning available instream habitat through
aggressive agonistic interactions with other juvenile fish (Quinn 2005). These 50 to 60 mm fish
are commonly referred to as “parr,” and will remain at this stage until they migrate to the ocean.
Typical parr rearing habitat consists of slow moving, complex pool habitat commonly found
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