The Washington Department of Fish and Wildlife (WDFW) has compiled information on bull trout habitat. They have a database that identifies known spawning areas. This data set combines the knowledge from biologists working for WDFW, U. S. Fish and Wildlife Service (USFWS), Tribes, and others. The data are current as of November, 2001.
There are no databases of known early tributary rearing areas. However, based on what is known of the biology of char, they would most typically be in the same general locations as the known spawning areas. It is important to note that where site knowledge demonstrates that this early tributary rearing occurs at locations away from the spawning grounds, then the proposed methodology will allow these areas to be protected in future rulemakings.
This database (often referred to as the “bullchar” database) forms the foundation of Ecology’s method of protecting char.
Ecology studied the locations of known spawning areas documented in the “bullchar” database and found that their occurrence is largely restricted to a relatively narrow range of elevation and stream order. Ecology used this pattern of elevation and stream order to deduce which streams would reasonably be expected to be potential char habitat.
The stream order concept (Strahler, 1952) is a method of classifying streams. Headwater streams are assigned a stream order of 1. When two 1st order streams join, they form a 2nd order stream. When two 2nd order streams join, they form a 3rd order stream, and so on. When a lower order stream joins and higher order stream (for example, a 1st order stream joins a 3rd order stream), the stream order does not change.1
Ecology found that most known spawning areas were in 1st, 2nd, and 3rd order streams. Limited spawning occurred in 4th order streams. The following table shows the stream orders of the known spawning streams:
Known Spawning Streams:
East Side West Side Combined 1
As the table shows, there is little difference between east side streams and west side streams. Approximately 92% of all known spawning occurs in 1st, 2nd, and 3rd order streams, so Ecology focused its efforts on those streams when developing the system for identifying char waters.
An analysis of all the spawning data quickly shows that known spawning areas are concentrated in higher elevation streams. For each known spawning stream, the lowest elevation was calculated.* The following table provides summary information of known spawning streams and their elevations:
Elevations (in feet) of Known Spawning Streams East Side West Side Number of Streams 77 67 Average Elevation
Lower 95th Percentile 1889 676
This analysis found that 94% of the known spawning areas were above 2000 feet on the east side and above 700 feet on the west side. Thus this elevation filter captures most of the known spawning streams.
Next: System for Identifying Char Waters
* Throughout this analysis, the lowest elevation of the stream or stream segment was used. Both the known spawning streams and the application of the elevation filter used the lowest elevation to maintain consistency and reduce any bias.
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