Oncorhynchus mykiss : The Quandary of a Highly Polymorphic Species

1. 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

2. 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.

3. 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.

4. 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 NMFS Policy and Criteria for Defining ESUs Formally adopted as a federal policy applicable to NMFS

5. 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: 1) substantially reproductively isolated from other conspecific population units, 2) represents an important component in the evolutionary legacy of the species. Separate ESUs

6. 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: ? 1) substantially reproductively isolated from other conspecific population units, 2) represents an important component in the evolutionary legacy of the species.

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

8. Evidence for or against reproductive isolation: Geographic distribution and physical barriers 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

9. Distribution and Physical Barriers: Three Patterns 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; 3. Trout are above a long-standing natural barrier and are outside of historic steelhead range.

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

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

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

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

14. Hood River Steelhead Pedigree (Ardren and Blouin) Parentage Assignment Rate Steelhead Mom; “Resident Dad” Two steelhead parents 0.5 1991 Parents 1995 Parents 0.45 F 1996 Parents r 0.4 e 1997 Parents 0.35 q Maybe Natural Strays u 0.3 e n 0.25 c Steelhead Dad; “Resident Mom” 0.2 y 0.15 0.1 0.05 0 Parent Pair Mom Only Dad Only Neither Parent

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

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

17. 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;

18. Three scenarios of trout and steelhead distribution: NOT reproductively isolated 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; Recent and Artificial 3. Trout are above a long-standing natural barrier and are outside of historic steelhead range. Reproductively Isolated Up to NMFS to decide final ESU boundaries.

19. 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 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.

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

21. Steelhead Basin-wide Adult Trout in 25 km Index Area, Upper Mainstem 12,000 10,000 120,000 8,000 Steelhead Basin-wide Adult Trout in Lower Mainstem 100,000 Number of fish 6,000 80,000 4,000 Number of fish 60,000 40,000 2,000 20,000 0 0 1988 1990 1998 1986 1992 1994 1996 2000 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Year Yakima Basin Lower Deschutes River Year Abundance: In areas of sympatry in the inland Columbia Basin, adult trout appear to comprise 90% to 95% of the adult O. mykiss present.

22. And therein lies the ESA quandary. ESUs may be secured from extinction risk by trout even while steelhead are in danger of extinction. If trout and steelhead are in the same ESUs... Trout (the ESUs) are still present everywhere steelhead have already become extinct. 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?