Oncorhynchus mykiss:

The Quandary of a Highly Polymorphic Speciesunder 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 Steelheadare Sympatric

Trout PopulationsIsolated above Dams,but within HistoricSteelhead Range

Trout PopulationsIsolated aboveNatural Barriers

Yakima steelheadcombined with othersto form the Mid-Columbia ESU

55

Genetics Survey of Trout and Steelhead(Pearsons et al.)

Unable to differentiatetrout from steelhead; but four Yakima steelhead populations were differentiated.

Genetics Evidence

Teanaway River, Yakima Basin

: Gene Flow

The O. mykiss problem:

Most samples were juvenilesfrom areas of steelhead/troutsympatry.

55

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

Populationsabove Waterfalls

Experimental Studies

Evidence that the life histories can produce the alternate life history

Parentage Assignment Rate

Hood River Steelhead Pedigree (Ardren and Blouin)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Parent Pair Mom Only Dad Only Neither Parent

Frequency

1991 Parents

1995 Parents

1996 Parents

1997 Parents

Two steelheadparents

Steelhead Mom;“Resident Dad”

Steelhead Dad;“Resident Mom”

MaybeNatural Strays

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

StsFxStsM

StsFxRbM

ResFxStsM

ResFxRbM

RbFxStsM

RbFx RbM

Crosses

0%

10%

15%

20%

25%

30%

35%

40%

45%

StsFxStsM

StsFxRbM

ResFxStsM

ResFxRbM

RbFxStsM

RbFx RbM

Crosses

Per

cen

t o

f re

leas

ed o

ffsp

rin

g

that

wer

e d

etec

ted

Grande Ronde Experimental Crosses (Ruzycki et al.)Detection of smolts at mainstem dams produced by crosses

Sts: Steelhead parentRes: Residual parent

(resident offspring of steelhead)Rb: Wild trout parent

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

StsFxStsM

StsFxRbM

ResFxStsM

ResFxRbM

RbFxStsM

RbFx RbM

Crosses

0%

10%

15%

20%

25%

30%

35%

40%

45%

StsFxStsM

StsFxRbM

ResFxStsM

ResFxRbM

RbFxStsM

RbFx RbM

Crosses

Per

cen

t o

f re

leas

ed o

ffsp

rin

g

that

wer

e d

etec

ted

Grande Ronde Experimental Crosses (Ruzycki et al.)Detection of smolts at mainstem dams produced by crosses

Sts: Steelhead parentRes: 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” steelheadand 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 distributionof the five listedColumbia Basin ESUs

Distribution of the ESUsif trout above the damsare 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.

Lower Deschutes River

0

20,000

40,000

60,000

80,000

100,000

120,00019

71

197

3

197

5

197

7

197

9

198

1

198

3

198

5

198

7

198

9

199

1

199

3

199

5

199

7

199

9

200

1

Year

Num

ber

of

fish

Steelhead Basin-wideAdult Trout in Lower Mainstem

0

2,000

4,000

6,000

8,000

10,000

12,000

198

6

198

8

199

0

199

2

199

4

199

6

199

8

200

0

Num

ber

of

fish

Year

Yakima Basin

Steelhead Basin-wideAdult 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 significantchange 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 everywheresteelhead have already become extinct.

If trout and steelhead are in the same ESUs...