Abstract
Summer Steelhead Distribution (CalFish)
June 2007
Version
This dataset depicts observation-based stream-level geographic
distribution of anadromous summer-run steelhead trout, Oncorhynchus mykiss
irideus (O. mykiss), in California. It was developed for the express purpose of
assisting with steelhead recovery planning efforts. The distributions reported
in this dataset were derived from a subset of the data contained in the Aquatic
Species Observation Database (ASOD), a Microsoft Access multi-species
observation data capture application. ASOD is an ongoing project designed to
capture as complete a set of statewide inland aquatic vertebrate species
observation information as possible. Please note: A separate distribution is
available for winter-run steelhead. Contact information is the same as for the
above.
ASOD Observation data were used to develop a network of stream
segments. These lines are developed by "tracing down" from each observation to
the sea using the flow properties of USGS National Hydrography Dataset (NHD)
High Resolution hydrography. Lastly these lines, representing stream segments,
were assigned a value of either Anad Present (Anadromous present). The end
result (i.e., this layer) consists of a set of lines representing the
distribution of steelhead based on observations in the Aquatic Species
Observation Database.
This dataset represents stream reaches that are
known or believed to be used by steelhead based on steelhead observations. Thus,
it contains only positive steelhead occurrences. The absence of distribution on
a stream does not necessarily indicate that steelhead do not utilize that
stream. Additionally, steelhead may not be found in all streams or reaches each
year. This is due to natural variations in run size, water conditions, and other
environmental factors. The information in this data set should be used as an
indicator of steelhead presence/suspected presence at the time of the
observation as indicated by the 'Late_Yr' (Latest Year) field
attribute.
The line features in the dataset may not represent the maximum
extent of steelhead on a stream; rather it is important to note that this
distribution most likely underestimates the actual distribution of steelhead.
This distribution is based on observations found in the ASOD database. The
individual observations may not have occurred at the upper extent of anadromous
occupation. In addition, no attempt was made to capture every observation of O.
mykiss and so it should not be assumed that this dataset is complete for each
stream.
The distribution dataset was built solely from the ASOD
observational data. No additional data (habitat mapping, barriers data, gradient
modeling, etc.) were utilized to either add to or validate the data. It is very
possible that an anadromous observation in this dataset has been recorded above
(upstream of) a barrier as identified in the Passage Assessment Database (PAD).
In the near future, we hope to perform a comparative analysis between this
dataset and the PAD to identify and resolve all such discrepancies. Such an
analysis will add rigor to and help validate both datasets.
This dataset
has recently undergone a review. Data source contributors as well as CDFG
fisheries biologists have been provided the opportunity to review and suggest
edits or additions during a recent review. Data contributors were notified and
invited to review and comment on the handling of the information that they
provided. The distribution was then posted to an intranet mapping application
and CDFG biologists were provided an opportunity to review and comment on the
dataset. During this review, biologists were also encouraged to add new
observation data. This resulting final distribution contains their suggestions
and additions.
Please refer to "Use Constraints" section
below.