Status of Winter Rearing Habitat In Four Coho Population Units, 2007 Report Number: OPSW-ODFW-2008-7

Identification Information

Citation

Originator: Romer, J., K. Anlauf, and K. Jones

Publish Date: May 2008

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: In a recent assessment of coastal coho salmon by the Oregon Department of Fish and Wildlife (2005), the authors concluded that productivity in 21 of 21 coastal coho populations was limited primarily (13) or secondarily (8) by the complexity of stream habitat used by juvenile coho during their first winter of freshwater residence. The Oregon Coast Coho Conservation Plan (Nicholas 2006), written in response to the assessment, concluded that recovery of coho populations will depend largely on improvement of freshwater habitat. The Conservation Plan (Nicholas 2006) presents population specific goals for the amount and quality of winter habitat needed to achieve desired status of coho populations. Monitoring objectives in the Plan are 1) describe the status of freshwater habitat in each population unit with a focus on features important to overwinter survival of juvenile coho, 2) estimate carrying capacity in each population unit with + 30% confidence, and 3) measure progress towards meeting the habitat goals of the Conservation Plan. This report describes the first two monitoring objectives for winter habitat in four population units: the Coquille, South Umpqua, Siuslaw, and Nehalem. Winter habitat surveys are conducted to describe the freshwater habitat conditions that may limit the survival of juvenile coho during the season at which the conditions are limiting. The Habitat Limiting Factors Model (Nickelson et al. 1992a, Nickelson et al. 1992b, Nickelson 1998) estimates the capacity of streams to support juvenile salmon based on quantitative descriptions of summer and winter habitat. The model assigns value to the size, type and complexity of habitat units, giving highest value to slow water pools such as alcoves and beaver ponds, and pools with large wood. Because winter habitat limits the capacity of most coastal streams to support juvenile coho (Rodgers et al. 2005), accurate estimates of winter habitat are essential to life cycle modeling and to meet objectives of the Conservation Plan. Rodgers et al. (2005) estimated potential carrying capacity of stream habitat within each coastal coho population unit, but statistical confidence was limited by the source and manipulation of the data. Although the data set was extensive, most of the reaches were not randomly selected, and a regression model was used to extrapolate conditions from summer to winter (Rodgers et al. 2005). Summer surveys provide applicable information, but at low flow conditions. Summer weather and stream flows are predictable and conducive to field work; study sites are more accessible, work days are longer and warmer, lower water levels enable walking in the channel more easily, and water clarity is high. However, while more difficult logistically, winter surveys provide estimates during high flow conditions thought to be most important to juvenile coho survival. The winter surveys are conducted during “base flow” when off-channel habitats and secondary channels are inundated, but not over floodplain. The winter 2007 survey sites were selected using the Generalized Random Tessellation Stratified (GRTS) sample design (Stevens 2002) from a pool of sites previously surveyed during summer. This provided an opportunity to describe status within coho population units and refine the summer to winter conversion regression model. More sites are visited during summer than winter, and the sample pool will expand if we can use summer surveys to predict winter conditions. A thorough description of seasonal habitat variation will determine the appropriateness of using summer habitat data to assess habitat conditions during the winter. The objectives of this report are to provide the status of winter habitat surveyed in 2007 in four Oregon coastal coho salmon (Oncorhynchus kisutch) population units (Nehalem, Siuslaw, Coquille, South Umpqua), estimate the potential winter capacity of streams within those population units, and describe the differences observed in stream habitat between winter and summer with emphasis on slow water and secondary channel habitats. We also performed a sensitivity analysis to determine the number of survey sites necessary to represent each population unit within the desired confidence recommended in the Conservation Plan (Nicholas 2006).

Purpose:

Time Period of Content:

Geographic Extent: North Coast, Mid Coast, Mid-South, and Umpqua

Status: Final

Use Constraints:

Format: PDF File

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Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the attached file(s).

Is a physical copy maintained for reference at Headquarters? No