Publications

### CONCLUSIONS

We concluded that, at least until further information becomes available, resident and potamodromous life-history forms of O. c. clarki should be considered part of the ESU that includes Umpqua River sea-run cutthroat trout. Therefore, the entity petitioned for listing (Umpqua River sea-run cutthroat trout) is not, by itself, an ESA species, and a determination of "not warranted" for the petition could be based this conclusion. However, a "not warranted" determination on this narrow point would not be a resolution of the issue. There remains the undisputed fact that sea-run cutthroat trout in the Umpqua River are very close to extinction, and this option would do nothing to alleviate this problem.

On the other hand, there are difficulties in developing a scientific basis to support a proposal to list some form of Umpqua River cutthroat trout under the ESA. Such a proposal would have to deal with three key issues that we were unable to resolve strictly on the basis of available scientific evidence:

- The geographic extent of the ESU. A proposal to list must include a   description of the boundaries of the "distinct population segment" being   considered as an ESA species. Although there is evidence to support an ESU in   the upper Umpqua River Basin (North and South Umpqua Rivers), it is unclear   whether the ESU should include the mainstem and/or lower Umpqua River   cutthroat trout or even coastal populations. The Biological Review Team did   not reach consensus on this issue.     
- Alsea River hatchery fish. A proposal to list would have to be based on   the premise that a component of the native, sea-run cutthroat trout still   exists, in spite of the extensive releases of Alsea River hatchery fish.   Although circumstantial evidence from population abundance and run-timing   suggests that a component of the native run persists, there are no data that   directly address the effects of the Alsea River fish on Umpqua River native   cutthroat trout.     
- Thresholds. A proposal to list would have to include a determination that   the "species" was threatened or endangered. Given the lack of abundance   information for nonanadromous cutthroat trout in the Umpqua River, a   threatened or endangered determination presumably would focus on the sea-run   component. This could be justified on the premise that anadromy is a   genetically-based trait and that its presence in Umpqua River O.   clarki contributes substantially to ecological/genetic diversity of the   ESU. However, the genetic basis of anadromy has not been studied in O.   clarki, and there is no direct information about the genetic   relationships between the various forms of the species in the Umpqua River.   

The lack of key scientific information for this petition is similar in some respects to the situation NMFS faced in its status review for Snake River sockeye salmon (Waples et al. 1991). At the time a determination had to be made regarding that petition, the Biological Review Team unanimously agreed that the scientific information available was not sufficient to determine with any degree of certainty whether anadromous fish returning to Redfish Lake were derived from the indigenous sockeye salmon population or merely products of seaward drift of kokanee. NMFS elected to take a conservative approach in that listing determination because the consequences of an erroneous decision not to list almost certainly would have been extinction of that sockeye salmon population. Information developed since the proposed listing has shown that the sockeye salmon population in Redfish Lake is genetically distinct and should be considered separately from the kokanee (Waples 1992). 

Given the extremely low numbers of sea-run cutthroat trout returning to Winchester Dam, a similar conservative approach could also be used with the Umpqua River cutthroat trout. However, there was only one key issue for Redfish Lake sockeye salmon that was unresolved at the time listing was proposed; there are three unresolved issues for the current petition. A listing proposal would have to be based on a conservative approach to each of the three unresolved issues. A framework for doing this would presumably involve the following assumptions: 

- All life history forms of O. clarki in the Umpqua River Basin are   an ESU.   
- This ESU represents the evolutionary legacy of the historical O.   clarki population prior to the releases of Alsea River hatchery fish.     
- All life-history forms of O. clarki in the Umpqua River Basin   have experienced extensive declines in abundance such that they are presently   threatened or in danger of extinction; or alternatively, although there is   little information regarding the abundance of non-anadromous O.   clarki in the basin, the depressed sea-run component of the population is   a substantial and important component of the ESU and its loss would compromise   the distinctness and viability of the inclusive ESU. 

### Prospects for Additional Information

Prospects for additional information that may help to resolve these key issues are mixed. It is unlikely that significant new information about the genetic basis of anadromy in cutthroat trout will be developed in the near future. However, it should be feasible to inventory resident and potamodromous populations and develop abundance estimates throughout the basin. Assuming that adequate samples can be obtained, it should also be possible to resolve the relationship of the remaining sea-run fish to the Alsea River hatchery stock. Oregon State University and the U.S. Forest Service are involved in two studies of genetic and life-history traits in cutthroat trout from Oregon to Alaska. When completed, these studies should provide important information that may provide insights into the unresolved issues for Umpqua River cutthroat trout 

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