Coho Life History Map

Unique Life Histories for Nehalem Basin Coho

1. 6th Field Spawners upstream of Humbug Cr confluence (including mainstem Nehalem above RM 90 at Vernonia). 

Unique Features: 

• Tuffaceous siltstone and sandstone / Marine sedimentary 

• High IP

• Exhibits the unique capability of surviving extremely high colloidal concentrations of suspended sediment year round (Crooked Cr)

Complex variations known to exist within each general Life History pattern:

• Overwinter in 6th field 

• Mainstem nomads that rear in estuary (spring, summer, winter)

• Mainstem nomads that do not reach estuary (summer rear in 2nd / 3rd order thermal refuge in tribs to mainstem / broad distribution)

1. 6th Field Spawners in Salmonberry / Cronin Cr / Cook / Lost

Unique features: 

• Tillamook volcanics

• Low IP

• North slope contributions (temp)

• Cronin Cr stock exhibits high c. shasta resistance. Indications from other hatchery studies conducted at the NF Nehalem hatchery suggest c. shasta resistance may be a genetic trait broadly distributed in wild Nehalem coho (Trask hatchery stock crosses w/ Fish hawk Lake stock)

Complex variations known to exist within each general Life History pattern:

• Overwinter in 6th field 

• Mainstem nomads that rear in estuary (spring, summer, winter)

• Mainstem nomads that do not reach estuary (summer rear in 2nd / 3rd order thermal refuge in tribs to mainstem / broad distribution)

1. 6th Field Spawners in NF Nehalem

Unique features: 

• High potential for exposure to genetic dilution from hatchery

• Differential fitness, productivity, hidden benefits

• Tuffaceous siltstone / sandstone (lower basin, unique from similar upper basin geologies because of varying temporal access that can dramatically effect run timing)

• High IP

Complex variations known to exist within each general Life History pattern:

• Overwinter in 6th field 

• Mainstem nomads that rear in estuary (spring, summer, winter)

• Mainstem nomads that do not reach estuary (summer rear in 2nd / 3rd order thermal refuge in tribs to mainstem / broad distribution)

1. 6th Field Spawners Fishhawk Cr

Unique Features: 

• Significant Lake rearing

• Exhibit c.shasta resistance (Lichatowich, 1985)

• Combined tuffaceous siltstone / sandstone and marine sedimentary

Complex variations known to exist within each general Life History pattern:

• Overwinter in 6th field 

• Over winter in Fish Hawk Lake

• Mainstem nomads that rear in estuary (spring, summer, winter)

• Mainstem nomads that do not reach estuary (summer rear in 2nd / 3rd order thermal refuge in tribs to mainstem / broad distribution)

1. 6th Field Spawners of the lower 5th Field, Foley Cr

Unique Features: 

• Lower Basin 

• North Slope (spring fed, extremely unique temperature profiles)

• Differential survival and growth rates associated w/ nomadic strategy 

• High potential for temporal differences in spawning and emergence

• Coevolution with viable chum salmon population

• Combined tuffaceous siltstone / sandstone and mafic intrusive rock

Complex variations known to exist within each general Life History pattern:

• Overwinter in 6th field 

• Mainstem nomads that rear in estuary (spring, summer, winter)

General environmental and biotic factors that have the capacity of influencing life history diversity in freshwater 

• Thermal barriers that develop in relation to changes in climactic conditions. An appropriate example is where low flow winter flow scenarios create both a temperature barrier (too cold) and a hydrologic barrier (low flows limiting access to natal 6th fields) for spawning migration. This scenario results in creating a survival advantage for late run timings that produce adults with a high condition factor capable of holding for long periods in mainstem habitats before initiating spawning migrations.

• Adult size that has the capacity of influencing escapement targets (stream size) and capitalizing on variable gravel sorts. Jacks and Jennys may be more effective at utilizing very small streams for spawning and incubation.

• The proliferation of beaver likely creates a unique coho life history strategy. Exceptional growth rates that alter outmigrant timing. This scenario results in survivors that may be more capable of avoiding predation.

Prepared by:

Steve Trask
Senior Fish Biologist
Bio-Surveys, LLC.