Restoring the Oregon Chub

An adult Oregon chub.

Photo Credit: Paul Scheerer

By Paul Scheerer

Oregon chub (Oregonichthys crameri) are small minnows endemic to the Willamette Valley of western Oregon. They were formerly common and distributed throughout the valley in off-channel habitat, such as beaver ponds, oxbows, stable backwater sloughs, and flooded marshes. In the last 100 years, these habitats have been drastically reduced due to changes in seasonal flows resulting from the construction of dams, channelization of the Willamette River and its tributaries, and draining of wetlands for bottomland agriculture. This loss of habitat, combined with predation by introduced non-native game fishes, led to a sharp decline in Oregon chub abundance and a restricted distribution. In 1993, the U.S. Fish and Wildlife Service listed this species as endangered.

The previous year, the Oregon Department of Fish and Wildlife initiated studies to describe the distribution and abundance of the Oregon chub, its historic habitats, and the aquatic assemblages in these habitats. At the time of listing, only nine populations were known to exist, and the species was found in only two percent of its historical range. In the past 17 years, biologists have conducted extensive surveys of nearly 1,000 offchannel (not connected to a river) habitats. In addition, a major recovery effort has focused on releasing Oregon chub into suitable isolated habitats within the species historical range. These actions have increased the known distribution of Oregon chub throughout the Willamette Basin.

Oregon chub are found almost exclusively with native species. They are rare where there are non-native predatory game fishes, such as largemouth bass, bluegills, and crappies. Several populations of Oregon chub have been extirpated, or declined dramatically, when non-native fish invaded or were illegally introduced.

The Oregon Chub Recovery Plan was completed in 1998. It states that, in order to downlist the species from endangered to threatened: 1) there must be 10 populations of Oregon chub containing at least 500 adults, 2) all 10 populations must be stable or increasing in abundance for five years, and 3) at least three populations must be located in each of the three recovery areas outlined in the plan.

A habitat restoration project for the Oregon chub on private land (top, during restoration; bottom, after project completion).

Photo Credit: Pau Scheerer

In 2007, we met these criteria. Currently, there are 34 populations of Oregon chub in the Willamette Basin. Twenty of these populations, including eight introduced populations, totaled 500 or more fish. Fourteen populations have exhibited a stable or increasing population trend for the past 5 years, with at least three populations located in each of the three recovery areas.

In 2007, the two most abundant chub populations were introduced populations that occur on private properties. Cooperation of private landowners has been instrumental to progress towards the species’ recovery and has resulted in several habitat restoration projects and reintroductions into suitable habitats on private lands. A programmatic Safe Harbor Agreement is being prepared to facilitate future introductions of Oregon chub at additional locations on private lands. (For more information on Safe Harbor Agreements, a conservation incentive program for landowners, visit http://www.fws.gov/endangered/esa-library/pdf/harborqa.pdf.)

Twenty of the 34 Oregon chub populations have a low probability of annual floodplain connectivity. Most are isolated from each other due to the location of their habitat, the reduced frequency and magnitude of flood events, and the presence of migration barriers, such as impassible culverts and permanent high beaver dams. Based on the threats posed by non-native fish, and the loss and fragmentation of suitable Oregon chub habitats, current recovery strategies have focused on managing Oregon chub populations in isolation. But this approach has potentially severe genetic consequences. At present, genetic exchange among Oregon chub populations is believed to be minimal. Isolating populations that would normally experience gene exchange can result in a general decline in genetic diversity within a population and a corresponding increase in genetic divergence among different populations.

In response to this concern, the Oregon Department of Fish and Wildlife teamed up with the Fish and Wildlife Service’s Conservation Genetics Laboratory to conduct a population genetics study. Although the results are preliminary, only one population showed evidence of a genetic bottleneck, and population structuring was consistent with the recovery areas defined in 1998.

The next logical approach to Oregon chub recovery is to integrate floodplain connectivity into conservation actions, allowing genetic exchange among populations. Unfortunately, non-native fishes remain one of the greatest threats to the Oregon chub. The floodplain connectivity needed to that ensure the genetic exchange could permit populations of non-native fishes to gain access to Oregon chub populations. Unauthorized introductions of non-native species remain another potential threat.

Recent river flow management plans have sought to restore floodplain processes by altering discharge from dams to mimic historical flows regimes, where practical, and reconnecting floodplain habitats. Future recovery efforts will aim to integrate habitat that is connected to the floodplain, research ways to reduce the adverse effects associated with non-native fishes, and maintain genetic diversity. We believe we can build on the successes we have already achieved.

Paul Scheerer, a biologist with the Oregon Department of Fish and Wildlife’s Native Fish Investigations Project, can be reached at 541-757-4263, ext. 257, or paul.scheerer@oregonstate.edu. For more information on the project, visit http://oregonstate.edu/Dept/ODFW/NativeFish/OregonChub.htm.