ODFW Oregon Plan Habitat Monitoring Program
for Coastal Basins

Habitat Surveys Study Area and Site Selection

STUDY AREA

Oregon Plan Habitat Surveys are designed to assess all streams within the range of coho salmon.  The target population of streams were contained within watersheds of western Oregon draining into the Pacific Ocean south of the Columbia River.  The area encompassed two Evolutionary Significant Units (ESU’s) for coho salmon: the Oregon Coastal ESU and the Southern Oregon/Northern California ESU. The Oregon Department of Fish and Wildlife (ODFW) has further divided the Oregon Coastal ESU into three Gene Conservation Areas (GCA) for coho salmon based on studies of genetic variation and life history traits (Kostow 1995).  For fishery management the North Coast GCA was further split into a North Coast and a Mid Coast GCA (Bodenmiller et al. 1997).  These five GCAs are used as the basis for monitoring coho habitat in Oregon coastal streams (Figure 1).

The target populations of streams for the study were based upon a hydrography data layer developed by the USGS at the 1:100,000 scale.  Streams upstream of large dams that blocked anadromous fish passage were removed from the selection frame.  A random tessellation stratified (RTS) design (Stevens 1997) was used to select potential sample site locations within the population of stream segments.  Stevens and Olsen (1999) described the RTS survey design as applied to the integrated monitoring of habitat, adult spawners, and juvenile salmonids for the ODFW.  The advantage of the RTS selection protocol was the selection of sites spread randomly across the landscape, better representing habitat conditions within a GCA, and reducing overall sample variance.  In all GCAs surveyed, samples were weighted to provide an equal number of sample sites (50).

Some sample sites were not surveyed.  The primary reason for not surveying a site was denial of access from landowners.  Additional sites were dropped because they were small (<0.6 km² catchment area), tidally influenced, or a result of errors in the selection coverage (Table 1).

The overall rate of access denial was higher in 2000 (12.5%) than 1999 (6%), and continued to encompass a large percent (45%) of private non-industrial sites.  As in previous survey seasons these unsurveyed sites contribute to a bias in the final dataset.  Historically, private non-industrial lands have had the lowest habitat quality (Thom et al. 1999).  Given the lower quality habitat that was observed on private non-industrial lands in the past, and the high percentage of these sites that have been unsurveyed between 1998 and 2000, all findings provide a biased estimate of conditions for private non-industrial ownership as well as the coast as a whole.

Table 1: Summary table of surveyed and not surveyed sites for 2006 season.

*Target sites are defined as sites selected in the annual sample draw that are surveyable.
**Non-Target sites are sites selected in the annual sample draw that were incorrectly identified on the base coverage and are not surveyable.  These sites include sites located in tidal areas, on small streams (upstream catchment area of <0.6 km² ) or are the result of an error on the GIS coverage. 
***P/A = Presence/Absence surveys using electrofishing.

SURVEY METHODS

Habitat survey

Channel habitat and riparian surveys were conducted as described by Moore et al. (1997) with some modifications.  Modifications to the survey methods included: survey of stream lengths of only 500-1000 m and measurement of all habitat unit lengths and widths (as opposed to estimation).  Ten percent of the sites were resampled with a separate two-person crew.  Repeat surveys were a randomly selected sub-sample from each geographic area and survey crew.  The repeat surveys were intended to measure within-season habitat variation and differences in estimates between survey crews. 

Fish survey

Fish presence/absence surveys using electofishing were conducted at habitat sites outside of known coho salmon distribution in all GCAs.   A complete description of the methods used is contained in ODFW (1998).  A coordinated but separate project within ODFW conducted coho salmon summer density estimates using snorkeling (Rodgers 2000).

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