Oregon Plan Aquatic Habitat Surveys
Habitat Surveys Study
Area and Site Selection
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 three Evolutionary Significant Units (ESUís) for
coho salmon: the Oregon Coastal ESU, the Lower Columbia River 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 Monitoring Areas (MA) for coho salmon
based on studies of genetic variation and life history traits (Kostow 1995).
For fishery management the North Coast MA was further split into a North
Coast and a Mid Coast monitoring area (Bodenmiller et al. 1997).
These six monitoring areas are used as the basis for monitoring coho habitat in
Oregon coastal streams.
Stream surveys are conducted
in the summer season for assessment of status and trends in stream habitat
at the monitoring area scale. In the winter, habitat surveys are
conducted to get estimates of habitat status at the population area scale.
More sampling details.
target populations of streams for the study are based upon a hydrography data
layer developed by the USGS at the 1:100,000k scale. The target populations of streams was updated in 2007 at the
1:24,000k 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) is 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 is the selection of sites spread randomly across the
landscape, better representing habitat conditions within a monitoring area and reducing
overall sample variance. In all
monitoring areas surveyed, samples are weighted to provide an equal number of sample sites
sample sites are not surveyed. The
primary reason for not surveying a site is denial of access from landowners.
Additional sites are dropped because they are too small (<0.6 km2
catchment area), too large (common in the Lower Columbia strata), tidally influenced, or a result of errors in the selection
coverage (Table 1).
habitat and riparian surveys are conducted as described by
Moore et al. (1997) with some modifications. Modifications
to the survey methods included: survey of stream lengths of only 500-1000m and
measurement of all habitat unit lengths and widths (as opposed to estimation).
Ten percent of the sites are re-sampled with a separate two-person crew.
Repeat surveys are a randomly selected sub-sample from each geographic
area and survey crew. The repeat
surveys are intended to measure within-season habitat variation and differences
in estimates between survey crews.
presence/absence surveys using electrofishing are conducted at habitat sites
outside of known coho salmon distribution in all monitoring areas.
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).