Factors that Influence Evolutionary Significant Unit Boundaries and Status Assessment in a Highly Polymorphic Species, Oncorhynchus mykiss, in the Columbia Basin; Information Reports 2003-04

Identification Information

Citation

Originator: Kathryn Kostow

Publish Date: October 2003

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Cedric Cooney

Job Position: Natural Resources Data and Systems Manager

Telephone: 503-947-6094

E-Mail Address: cedric.x.cooney@odfw.oregon.gov

Description

Abstract: The species Oncorhynchus mykiss expresses a complex array of life histories across much of its range as well as considerable geographic variation. Several subspecies have been proposed (Behnke 1992), although none of them are formally recognized. Two of the proposed subspecies in North America include both trout and steelhead life histories: O.m. irideus, or Coastal rainbow/steelhead, and O.m. gairdneri, or Inland redband/steelhead. A third subspecies that includes an anadromous life history occurs in Asia, while all other North American subspecies are entirely trout. In the Pacific Northwest, the boundary between the coastal and inland subspecies occurs in the Columbia Gorge, where the Columbia River cuts through the Cascade Mountain Range. The steelhead and trout life histories within these two subspecies are genetically more similar to each other than to fish with the same life history in the other subspecies, indicating that the different life histories within a geographic area share an evolutionary origin (Allendorf 1975). Recent molecular systematic surveys suggest that this proposed taxonomic model of North American 0. mykiss subspecies may be over simplified and inaccurate (Currens 1997, Busby et al. 1996, F. Utter, U. of Washington); however, it remains the available model until final revisions to the taxonomy are adopted. The NOAA Fisheries Service (NMFS) further divided 0. mykiss into multiple "Evolutionarily Significant Units" (ESUs)(Waples 1991, 56 FR 58612, Waples 1995) for listing consideration under the federal Endangered Species Act (ESA). The ESA considers "distinct" populations of taxonmnic species to be "species" eligible for legal protection (16 U.S.C. 1532[161). NMFS adopted the concept of ESUs to serve as distinct population segments in their ESA listing decisions, along with specific criteria for defining them. Evidence for whether or not rainbow trout and steelhead are in the same ESUs is presented in this report according to the criteria provided by NMFS policy (56 FR 58612). The U.S. Fish and Wildlife Service (USFWS) likewise recognizes "Distinct Population Segments" (DPSs) that may be listed under ESA. The agencies share jurisdiction over 0. mykiss for ESA decisions, with NMFS overseeing the anadromous steelhead and USFWS overseeing the freshwater trout. NMFS has described ESUs for all Northwest steelhead, whether they have been listed or not (Busby et al. 1996); however, the USFWS has not generally described DPSs for Northwest 0. mykiss trout. During the original coast-wide status review of steelhead conducted in the 1990s, the NMFS Biological Review Team concluded that, in general, 0. mykiss trout are part of steelhead ESUs in cases where the two forms are sympatric and have an opportunity to interbreed (Busby et al. 1996). The review team was less conclusive about whether trout above artificial barriers were part of the ESUs. Trout that are sympatric with steelhead were also included in the ESUs by NMFS in the final listing determinations, but they were not listed. The steelhead in five of the ESUs in the Pacific Northwest were listed, including the Lower Columbia (63 FR 13347), Willamette, Mid-Columbia (64 FR 14517), Upper Columbia and Snake ESUs (62 FR 43937), all of which are in the Columbia Basin. As a result of two recent court cases NMFS is now reexamming the biological relationship between trout and steelhead populations in the ESUs where steelhead are listed and is reassessing the extinction risk of the whole ESUs from the perspective of both life histories. First, the Hogan decision in Oregon concluded that the Services may describe distinct population segments for ESA listing, but once ESUs or DPSs are described, the Services cannot list only part of one of one of them (Alsea Valley Alliance v. Evans [161 F.Supp. 2d 1154, D. Oreg. 2001]). So if NMFS finds trout to be part of an ESU along with steelhead, the Service cannot assess the extinction risk of only the steelhead in the ESU or list only the steelhead. Second, lawsuits in California about non­anadromous 0. mykiss upstream of man-made barriers (mostly impassible dams) made a similar argument, stating that such populations are related to the steelhead populations below the barriers and should be included in the ESUs and listed (EDC v. Evans, SACV- 00-1212-AHS (EEA), United States District Court, C.D. California). The purpose of this report is to provide more detailed information about trout and steelhead in the Columbia Basin listed ESUs. This report will address two major issues. The first section provides information that will be used to review whether trout and steelhead populations are biologically part the same ESUs, as defined by NMFS criteria. The second section provides information that will be used to review the extinction risks of entire ESUs if trout are considered along with steelhead. A similar, separate report is being prepared for California ESUs where steelhead are listed.

Purpose:

Time Period of Content:

Geographic Extent: Columbia River Basin

Status: Final

Use Constraints:

Format: pdf

Data Quality Information

Lineage-Source: This document was prepared under an Interagency Personnel Agreement (IPA) between Oregon Department of Fish and Wildlife, Fish Division, Portland OR. and NOAA Fisheries, NW Fisheries Science Center, Seattle WA. Funding for this project was provided by NOAA Fisheries and Oregon Department of Fish and Wildlife.

Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the attached file(s).

Is a physical copy maintained for reference at Headquarters? Yes