Abstract
Winter Steelhead Distribution (CalFish)
June 2007
Version
This dataset depicts observation-based stream-level geographic
distribution of anadromous 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 summer-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), or Unsp Present (Unspecified
O. mykiss 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 were provided the opportunity to review and suggest edits
or additions during the review. Initially 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.