Olympic Peninsula Regional Anadromous Fish Habitat Intrinsic Potential Modeling

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PDF Document Phase II Report FEBRUARY 2013

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A Discusssion on the Life Cycle of Coho Salmon



Coho salmon generally don't use the mainstem Quillayute except for migration to and from upstream habitat. The Dickey system (and lake) are utilized heavily nearly to their headwaters. The Boachiel and Calawah systems, barring natural barriers, are heavily utilized.

The Hoh river up to Glacier creek and the lower reaches of the South Fork are habitat for these fish, however, most tributaries are too steep. Brandon, Nolan and Winfield creeks comprise good habitat as do the lower reaches of the tributaries in the Hoh Valley[a].


The mainstem Queets is not utilized to any great degree by Coho for spawning. However, upstream tributaries are used extensively. Spawning is limited to the lower gradient reaches in the Queets mainstem above Tshletshy creek. The tributaries on the north side of the Queets are limited to their lower reaches, except for the Clearwater, whose entire system except for the Sollecks river are considered good spawning habitat[b].


The Bear river is considered one of the major spawning grounds for Coho in Willapa bay. The smaller tributaries are fertile grounds for Coho, particularly the upper reaches as the lower reaches have been impacted by logging in the past. Independent drainages in the Bear subwatershed are also good spawning and rearing habitat[c].

[a] WDFW 2003 WRIA 20 Salmonid Fish Inventory

[b] WDFW 2003 WRIA 21 Salmonid Fish Inventory

[c] WDFW 2003 WRIA 24 Salmonid Fish Inventory

Coho life cycle habits

Life Cycle Timing

These tables provide information on the timing of all life cycle stages for all OWC Coho runs. Note that they are part of the WRIA Salmonid Fish Inventory and Distribution provided by WDFW in 2003.

See Coho freshwater life cycle timing table for WRIA 20 here.

See Coho freshwater life cycle timing table for WRIA 21 here.

See Coho freshwater life cycle timing table for WRIA 21 here.

The bipartite nature of the rearing portion of the Coho life cycle is well documented.

Summer rearing

In this exerpt, summer rearing habits in other regions as recorded fit well with what is known for OWC Coho populations:

"...they redistribute themselves and move into small tributary streams to overwinter, with the fall freshets. Observed movement 200-400m upstream (from summer areas) to enter small tribs and sloughs for overwintering - moving upstream into 'side creeks' that remain stable during the winter...[1]"

The italicized portion of the excerpt above is retained to show the variability of habit in other regions. This life cycle habit does not appear to have not been reported for OWC Coho populations.

Another observation worth noting as relates to Oregon Coast Coho populations where Burnett et al with introduce considerable discussion of gradient, drawing from other workers. Table 1 was one of the sources used to populate the summer gradient curve:

"Coho salmon in the Coastal Province of Oregon rear typically in low-gradient stream reaches and decrease in density as gradients increase to about 10% (Nickelson 1998). For example, Schwartz (1990) found a negative relationship between the density (number/100m) of juvenile coho salmon and channel gradient for gradients between 0.5% to 7% and the greatest densities of coho salmon in gradients below 2–3%. Similarly, Hicks (1989) observed juvenile coho salmon predominately in streams with gradients less than 2%. Thus for coho salmon, we assigned the highest value to channel gradients less than or equal to 2% and lower values to gradients exceeding this (Table 1). We assumed that coho salmon did not use areas upstream of reaches with gradients greater than 10%.[2]"

Agrawal, et al describe summer rearing habit in terms of structures as refugia from high stream discharge, with reference to gradient and constraint as well:

"During the summer, juvenile coho salmon generally prefer pool habitats over runs and riffles (Bisson et al., 1988). Juvenile coho salmon often move out of the main channel and seek refuge in side channels, alcoves, and other off-channel habitats during periods of high stream discharge (Tschaplinski and Hartman, 1983; Meehan and Bjornn, 1991; Bell et al., 2001). Together, these attributes and behaviors likely explain why juveniles are most abundant in low-gradient (usually <2%-3% but occasionally up to 5%), unconstrained reaches as opposed to constrained reaches or steeper headwater streams.[3]"

Winter rearing

Groot and Margolis record winter rearing habits very similar to what is seen in OWC Coho populations. Note commentary on velocities and temperature as "incentives":

"...In other systems, some fish move downstream (ie, as much as 38km) from summer rearing areas before entering tributaries. Distance move appears to be related to the flow rate of the tributary stream. Fish move into these areas to avoid freshets - best areas are areas with spring-fed ponds adjacent to the main stream or protected, slow flowing side channels (that may only be wetted in winter), as well as beaver ponds. Coho move into areas with deeper water (>45cm) and lower velocities (15 cm/s), esp if temp drops below 7degC. In the spring, prior to outmigration, there is a strong movement of juveniles back to the mainstem river or tributary.[4]"

Relationship with Steelhead populations

Agrawal et al report, citing other authors, the nature of the affinity of Coho and Steelhead populations for one another, in agreement with what was voiced by the participants at the workshop and what may be considered as resource partitioning between the two species:

"Juvenile (winter) steelhead The juvenile phase spans at least one summer and one winter in freshwater, but is more variable and of greater maximum duration than is observed for coho salmon. Following emergence in spring, steelhead fry typically adopt feeding stations in shallower portions of riffles or pools, moving into progressively faster and deeper water as they grow (Bisson et al., 1988).[5]"

The above except describes a situation where young Steelhead come into competitive conflict with Coho spawned during the same period. Note below their adaptation to displacement to riffles in response:

"Juvenile steelhead exhibit a streamlined body morphology that is thought to be an adaptation for life in faster water currents (Bisson et al., 1988). Although steelhead tend to prefer and grow faster in pool habitats, as young-of-the-year, they are commonly displaced to riffle habitats through competitive interactions with larger, more aggressive coho salmon when the latter are abundant (Bugert and Bjornn, 1991; Young, 2004).[6]"

Here, a description of how the older juveniles of each species respond in a fashion that can be construed as further resource partitioning:

Such displacement is not observed for older, larger juvenile steelhead. The spawning distribution of steelhead overlaps with that of coho salmon; however, because steelhead tend to prefer higher gradients (generally 2-7%, though they may be found in reaches with gradients up to 12% or more), their distribution tends to extend farther upstream. In some watersheds, steelhead will even spawn in ephemeral streams, with juveniles migrating downstream to permanent waters to rear.[7]"

[1] Groot and Margolis (eds.) 1991

[2] Burnett, 2003

[3] Agrawal et al 2005

[4] Groot and Margolis (eds.) 1991

[5] Agrawal et al 2005

[6] Ibid.

[7] Ibid.