Willamette BiOp - Genetic Stock Identification and Relative Natural Production of Willamette River Steelhead

Identification Information

Citation

Originator: ODFW

Publish Date: August 2013

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Jeremy Romer

Job Position: Assistant Project Leader

Telephone: 541-757-4113

E-Mail Address: jeremy.d.romer@odfw.oregon.gov

Description

Abstract: We used genotypic data from 15 microsatellite loci to characterize the stock structure of Oncorhynchus mykiss in the upper Willamette River basin. We then used two analytical approaches, implemented in the programs ONCOR and STRUCTURE, to assign (presumably) natural-origin, unmarked fish to their most likely reporting group or hybrid class. We investigated sibling relationships among unknown samples with the program ML RELATE. In the upper Willamette River, O. mykiss genetic structure can be characterized by four principal groups: summer steelhead of Skamania stock ancestry, eastern tributaries winter steelhead, western tributaries winter steelhead and resident rainbow trout. We found that about 10% of unmarked juvenile O. mykiss sampled at Willamette Falls in 2009-2011 were summer steelhead and that an additional 10% of samples were summer x winter steelhead hybrids. Most O. mykiss sampled from the McKenzie River were either summer steelhead or summer x winter steelhead hybrids. Natural production of pure summer steelhead appeared to be very low in the North and South Santiam rivers, though summer steelhead hybrids represented 11.1% and 14.8% of samples. Results from ML RELATE analyses appeared unreliable and inconclusive, and may have been limited by low genetic diversity among summer steelhead samples. We provide several recommendations to better understand and reduce potentially negative interactions between hatchery summer steelhead and native upper Willamette River O. mykiss populations. These include reductions in adult steelhead on natural spawning grounds, improved reproductive isolation between hatchery and native populations and additional research to evaluate genetic integrity within and among O. mykiss populations.

Purpose: In the upper Willamette River (UWR) basin, Oncorhynchus mykiss is represented by both resident rainbow trout and anadromous steelhead. Native winter steelhead typically return to the Willamette River from the ocean between February and May, then spawn (March-June) in the Molalla, North Santiam, South Santiam, and Calapooia rivers (Figure 1; ODFW and NMFS 2011). Some winter steelhead also spawn in westside tributaries of the Willamette River, such as the Tualatin, Yamhill, and Luckiamute rivers. Winter steelhead are rarely observed in the McKenzie or Middle Fork Willamette rivers and these subbasins are not considered to be critical habitat for the UWR steelhead distinct population segment (DPS) (NMFS 2012; ODFW and NMFS 2011). Much of the historic spawning habitat for UWR winter steelhead became inaccessible to the species in the mid-1960s, with the construction of high-head Willamette Project dams on the North and South Santiam rivers (NMFS 2008). In 1966, the Oregon Department of Fish and Wildlife (ODFW) initiated a summer steelhead hatchery program to mitigate for winter steelhead habitat losses caused by Willamette Project dams and to provide an enhanced sport fishery in the Willamette River basin. Summer steelhead are not native to the Willamette basin, and Skamania stock steelhead from Washington State were used to found hatchery broodstocks. Adult summer steelhead typically return to the UWR basin between March and October, and spawn timing can overlap with native winter steelhead that typically spawn in March and April (Firman et al. 2004). Since 1984, all juvenile hatchery summer steelhead released into the Willamette River have been marked by removing the adipose fin to distinguish them from natural origin steelhead. Marked summer steelhead have been observed on spawning grounds (Schroeder et al. 2006), raising concerns about negative ecological interactions and genetic introgression with native winter steelhead in the upper Willamette River Evolutionarily Significant Unit, which are listed as Threatened under the Federal Endangered Species Act (NMFS 1999). These concerns prompted development of Reasonable and Prudent Alternative (RPA) 9.5.2.1 (NMFS 2008), which recommended implementation of a study to “determine the extent of summer steelhead reproduction in the wild” by collecting “tissue samples from juvenile steelhead for genetic analysis to determine if offspring are of winter- or summer-run origin.” In addition, RPA 6.1.9 (Future Summer Steelhead Management Actions) states that, “The Action Agencies, in cooperation with ODFW, will implement future management actions aimed at reducing the impacts of the summer steelhead hatchery program on ESA-listed species.” Finally, the Upper Willamette River Conservation and Recovery Plan for Chinook Salmon and Steelhead (ODFW and NOAA 2011) listed interbreeding with summer steelhead as a key threat for winter steelhead in the North and South Santiam rivers (among others) and noted that the impact of genetic introgression and past or current hatchery practices is largely unknown.

Time Period of Content:

Geographic Extent: Tualatin, North Yamhill, South Yamhill, Luckiamute, Marys, Pudding, Molalla, North Santiam, South Santiam, and Calapooia rivers

Status: Final

Use Constraints:

Format: PDF

Data Quality Information

Lineage-Source: Task Order Number: W9127N-10-2-0008-0015 Work Completed for Compliance with the 2008 Willamette Project Biological Opinion, USACE funding: 2012

Data Information

No data information was supplied.

Entity and Attribute Information

Attributes Description: Field attribute information is available in the database table field descriptions.

Is a physical copy maintained for reference at Headquarters? No