12-Month Finding on a Petition To List Summer-Run Steelhead in Northern California as Endangered Under the Endangered Species Act

We, NOAA Fisheries, announce a 12-month finding on a petition to delineate Northern California (NC) summer-run steelhead as a distinct population segment (DPS) of West Coast steelhead (Oncorhynchus mykiss), and to list that DPS as endangered under the Endangered Species Act (ESA). We have completed a comprehensive DPS analysis of NC summer-run steelhead in response to the petition. Based on the best scientific and commercial data available, including the DPS configuration review report, we have determined that listing NC summer-run steelhead as an endangered DPS is not warranted. We determined that summer-run steelhead in the NC steelhead DPS do not meet the criteria to be considered a DPS separate from winter-run steelhead. We also announce the availability of the DPS configuration review report prepared pursuant to the ESA for the NC steelhead DPS.

Frequently Asked Questions

On November 15, 2018, NOAA Fisheries received a petition from Friends of the Eel River to list Northern California summer-run steelhead as an endangered Distinct Population Segment (DPS) under the Endangered Species Act (ESA). Currently, Northern California summer-run steelhead are part of the Northern California steelhead DPS—which includes both winter-run and summer-run steelhead.  This DPS has been listed as threatened under the ESA since June 7, 2000, and was reaffirmed on May 26, 2016.  The petitioner requested that Northern California summer-run steelhead be considered as a separate DPS and listed as endangered.

On April 22, 2019, we announced that the petition presented substantial scientific information indicating that the petitioned action may be warranted and that we were initiating a status review. 

NOAA Fisheries now announces its final determination on the petition. We find that Northern California summer-run steelhead do not constitute a DPS. Accordingly, Northern California summer-run steelhead does not meet the definition of a species; and, thus, Northern California summer-run steelhead does not warrant listing as endangered.

What’s the difference between a “species” and a “DPS”?

The ESA defines “species” to include any “distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature.” NOAA Fisheries and the U.S. Fish and Wildlife Service jointly published a policy regarding the recognition of DPSs of vertebrate species under the ESA (DPS Policy, 61 FR 4722; February 7, 1996). A DPS is a vertebrate population or group of populations that are markedly separated from other populations of the species and are biologically and ecologically important to the entire species.

What criteria do we use to identify DPSs?

We consider the following when identifying a DPS: (1) The discreteness of the population segment in relation to the remainder of the species; and (2) the significance of the population segment to the species. 

A population segment may be considered discrete if:

• it is markedly separated from other population segments; or
• it is delimited by international governmental boundaries.

Factors considered when evaluating significance may include, but are not limited to: 

• the population exists in an unusual or unique area;
• the loss of the population would result in a significant gap in the range of a species;
• the population segment represents the only surviving natural occurrence of the species; or
• the population differs markedly from other populations in its genetic characteristics.

What is Run-timing?

The time of year in which adult steelhead return to freshwater prior to spawning and their state of sexual maturity has been used to identify different “runs” of steelhead. Steelhead express two major run-types. Summer-run adult steelhead return to fresh water between May and October in a sexually immature condition. After several months in freshwater, summer steelhead mature and spawn. Winter-run adult steelhead return to freshwater between November and April with well-developed gonads and spawn shortly thereafter.

What is the Greb1L gene?

Scientists have discovered that genetic material from a portion of the genome (i.e., DNA) that includes the Greb1L gene is connected to run-timing in Chinook salmon and steelhead. Scientists characterize the Greb1L region as having two different forms (alleles) that can occur in one of three different combinations: individuals with two early run-timing alleles (summer run-timing homozygotes), individuals with two late run-timing alleles (winter run-timing homozygotes), and heterozygous individuals with one allele for the early and one for the late run-timing.

Why don’t you think that Northern California summer-run steelhead are a DPS?

The available data indicate that summer-run steelhead are not markedly separated from winter-run steelhead, as the two groups maintain an ongoing and interconnected genetic legacy with life histories that are not substantially reproductively isolated from each other.

Researchers have found new evidence demonstrating that genetic material from a portion of the genome, including the Greb1L gene (otherwise referred to as the Greb1L region of the genome), is strongly associated with run-timing in steelhead. However, genetic variation is not uniquely partitioned into summer-run and winter-run steelhead DPSs, but is broadly distributed across a range of interconnected populations with variable characteristics. Greb1L-region variation includes the widespread occurrence of heterozygotes and the presence of both ‘summer’ and ‘winter’ homozygotes in many populations without documented expression of the summer run-timing.

With such widespread distribution of genetic variation, matings between steelhead with alternate Greb1L-region genotypes is not uncommon. Such matings may result in full-sibling families with a mix of different Greb1L-region genotypes. Thus, designation of separate summer- and winter-run DPSs would both ignore the contribution of Greb1L-heterozygous individuals to these populations and potentially create situations in which siblings of these matings would be divided into different ‘species’ under the ESA. This new understanding of the Greb1L gene does not fundamentally alter our understanding of the evolutionary dynamics of this DPS.

Retention of both life-history types in a single DPS does not indicate a lack of recognition that summer-run steelhead are an important component of the DPS. Rather, it is an acknowledgment that the run-types are fundamental parts of the genetic diversity of the listed unit as a whole and should not be separated from each other.    

What information did NOAA Fisheries consider in deciding whether listing was warranted?

Our decision is based on the best scientific and commercial data available, as required by the ESA. We reviewed materials presented by the petitioner, information we received in response to the 90-day finding, and analyses by scientists from NOAA Fisheries’ Southwest and Northwest Fisheries Science Centers who have expertise in the species and their genetic makeup.