Oncorhynchus mykiss : The Quandary of a Highly Polymorphic Species under the U.S. Endangered Species Act by: Kathryn Kostow Oregon Department of Fish and Wildlife

In the late 1990s, steelhead populations in most of the Columbia Basin and California were listed as threatened or endangered under the U.S. Endangered Species Act. Resident life histories of Oncorhynchus mykiss were not included in the listings. This decision was challenged legally.

Components of the ESA quandary: “Distinct” populations of a taxonomic species can be listed as “species” under ESA; “Distinct” is not defined by the act. NMFS adopted criteria for defining “Evolutionarily Significant Units” (ESUs) to serve as their “distinct” populations for listing purposes; Consistent with their criteria, NMFS originally found that sympatric trout and steelhead are in the same ESU; The USFWS and NMFS share ESA jurisdiction over Oncorhynchus mykiss, with the USFWS responsible for trout and NMFS responsible for steelhead; The agencies disagreed about the need to list this species. Steelhead in many ESUs were listed but the trout were not. NMFS was sued for listing only part of their ESUs.

NMFS Policy and Criteria for Defining ESUs An ESU is “… a population (or group of populations) that 1) is substantially reproductively isolated from other conspecific population units, and 2) represents an important component in the evolutionary legacy of the species.” Waples 1991 Formally adopted as a federal policy applicable to NMFS

Trout and steelhead could be combined into a single ESU Or each life history could qualify as their own ESU depending on whether or not they meet both criteria: 2) represents an important component in the evolutionary legacy of the species. 1) substantially reproductively isolated from other conspecific population units,

Trout and steelhead could be combined into a single ESU Or each life history could qualify as their own ESU depending on whether or not they meet both criteria: 2) represents an important component in the evolutionary legacy of the species. 1) substantially reproductively isolated from other conspecific population units,

Frequent interbreeding is not necessary. NMFS combined life histories in several ESUs: Summer & winter steelhead, spring & fall chinook, etc. 1) substantially reproductively isolated from other conspecific population units? ESUs may include multiple “demographically independent” populations. Gene flow may be historic but recent, periodic or rare. ESUs are large-scale groupings. To be combined, trout & steelhead only need to interbreed to the same degree as populations in other ESUs. What has NMFS done before?

Evidence for or against reproductive isolation: Genetic evidence Otolith data Life history data: spawning time and location Observations of the life histories spawning together Evidence that the life histories can produce the alternate life history Geographic distribution and physical barriers

Distribution and Physical Barriers: Three Patterns 3. Trout are above a long-standing natural barrier and are outside of historic steelhead range. 1. The two life histories are currently sympatric; 2. Trout are above an artificial barrier that now blocks steelhead access into an area where the two life histories were historically sympatric;

Trout and Steelhead are Sympatric Trout Populations Isolated above Dams, but within Historic Steelhead Range Trout Populations Isolated above Natural Barriers

Yakima steelhead combined with others to form the Mid- Columbia ESU Genetics Survey of Trout and Steelhead (Pearsons et al.) Unable to differentiate trout from steelhead; but four Yakima steelhead populations were differentiated. Genetics Evidence Teanaway River, Yakima Basin : Gene Flow The O. mykiss problem: Most samples were juveniles from areas of steelhead/trout sympatry.

Other Genetics Surveys: Natural and Artificial Barriers Waples: North Fork Clearwater Leary: Snake River Populations above Dams Currens et al.: White River Knudsen et al.: Kootenai Populations above Waterfalls

Experimental Studies Evidence that the life histories can produce the alternate life history

Parentage Assignment Rate Hood River Steelhead Pedigree (Ardren and Blouin) Parent Pair Mom Only Dad Only Neither Parent F r e q u e n c y 1991 Parents 1995 Parents 1996 Parents 1997 Parents Two steelhead parents Steelhead Mom; “Resident Dad” Steelhead Dad; “Resident Mom” Maybe Natural Strays

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% StsFx StsM StsFx RbM ResFx StsM ResFx RbM RbFx StsM RbFx RbM Crosses 0% 10% 15% 20% 25% 30% 35% 40% 45% StsFx StsM StsFx RbM ResFx StsM ResFx RbM RbFx StsM RbFx RbM Crosses Percent of released offspring that were detected Grande Ronde Experimental Crosses (Ruzycki et al.) Detection of smolts at mainstem dams produced by crosses Sts: Steelhead parent Res: Residual parent (resident offspring of steelhead) Rb: Wild trout parent

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% StsFx StsM StsFx RbM ResFx StsM ResFx RbM RbFx StsM RbFx RbM Crosses 0% 10% 15% 20% 25% 30% 35% 40% 45% StsFx StsM StsFx RbM ResFx StsM ResFx RbM RbFx StsM RbFx RbM Crosses Percent of released offspring that were detected Grande Ronde Experimental Crosses (Ruzycki et al.) Detection of smolts at mainstem dams produced by crosses Sts: Steelhead parent Res: Residual parent (resident offspring of steelhead) Rb: Wild trout parent

Summary of other evidence: Extensive overlap of trout and steelhead spawning times and distributions; Trout and steelhead observed on the same redds, apparently spawning together; most frequently male trout acting like jacks; Many steelhead (and fluvial and adfluvial trout) sex ratios are 60% to 80% females suggesting some males in the populations are resident;

Three scenarios of trout and steelhead distribution: 3. Trout are above a long-standing natural barrier and are outside of historic steelhead range. 1. The two life histories are currently sympatric; 2. Trout are above an artificial barrier that now blocks steelhead access into an area where the two life histories were historically sympatric; Up to NMFS to decide final ESU boundaries.

What is the extinction risk of an ESU that includes both life histories? Previous NMFS status reviews only “counted” steelhead and assessed the extinction risk of only steelhead. The status and extinction risk of a steelhead/trout ESU may be quite different than that of just the steelhead: Distribution Population productivity Population structure Diversity Abundance Assuming that trout and steelhead are combined in ESUs

Distribution: Current distribution of the five listed Columbia Basin ESUs Distribution of the ESUs if trout above the dams are included.

Abundance: In areas of sympatry in the inland Columbia Basin, adult trout appear to comprise 90% to 95% of the adult O. mykiss present. 0 2,000 4,000 6,000 8,000 10,000 12, Number of fish Year Yakima Basin Steelhead Basin-wide Adult Trout in 25 km Index Area, Upper Mainstem

ESUs may be secured from extinction risk by trout even while steelhead are in danger of extinction. And therein lies the ESA quandary. The loss of steelhead would constitute a significant change in the character of an ESU. ESA speaks clearly about avoiding extinction. What does ESA say about avoiding a change in character? Trout (the ESUs) are still present everywhere steelhead have already become extinct. If trout and steelhead are in the same ESUs...