Introduction

The Oregon chub was listed as endangered in 1993. A recovery plan was published in 1998. Critical habitat was designated on March 10, 2010. The species' status has recently improved, and on April 23, 2010, the USFWS changed the Endangered Species Act classification of the Oregon chub from endangered to threatened. On February 4, 2014, the USFWS announced a proposal to remove the Oregon chub, and its critical habitat, from the list of Endangered and Threatened Species.

Historical Status and Current Trends

Oregon chub are endemic to the Willamette River Valley of western Oregon. Although information is scarce, the Oregon chub probably occurred throughout the lower elevations of the Willamette River valley. Historical records indicate that Oregon chub were found as far downstream as Oregon City and as far upstream as Oakridge. Historical records also report Oregon chub were collected from the Clackamas River, Molalla River, South Santiam river, North Santiam River, Luckiamute River, Long Tom River, McKenzie River, Mary's River, Coast Fork Willamette River, Middle Fork Willamette River, and the Willamette River from Oregon city to Eugene.

When the species was listed in 1993, there were eight known populations.  By 2007, there were 38 known populations and this met the recovery criteria for downlisting (changing the classification from endangered to threatened).  The USFWS downlisted Oregon chub to threatened status in 2010.  Currently, there are 50 known populations; 19 of these populations have stable or increasing seven-year abundance trends.  The improved status is attributed to successful introduction of Oregon chub into new locations within their historical range and the discovery of new, previously undocumented populations. The populations are found in the Santiam River, Middle Fork Willamette River, Coast Fork Willamette River, McKenzie River, and several tributaries to the Willamette River downstream of the Coast Fork/Middle Fork confluence.

Description and Life History

The Oregon chub is a small minnow with an olive-colored back grading to silver on the sides and white on the belly. Adults are typically less than nine centimeters (3.5 inches) in length. Scales are relatively large with fewer than 40 occurring along the lateral line; scales near the back are outlined with dark pigment. Adults feed in the water column on the tiny larvae of aquatic invertebrates, such as mosquitos and other insects. Spawning occurs from the end of April through early August when water temperatures are between 16 degrees and 28 degrees C (60 degrees and 82 degrees F). Only males larger than 25 millimeters (1 inch) spawn, and males more than 35 millimeters (1.4 inches) defend territories in or near vegetation. Females can lay several hundred eggs.

Habitat

Oregon chub are found in slack water off-channel habitats such as beaver ponds, oxbows, side channels, backwater sloughs, low gradient tributaries, and flooded marshes. These habitats usually have little or no water flow, silty and organic substrate, and aquatic vegetation as cover for hiding and spawning. The average depth of Oregon chub habitats is typically less than two meters (six feet) and the summer water temperature typically exceeds 16 degrees C (61 degrees F). Adult Oregon chub seek dense vegetation for cover and frequently travel in the mid-water column in beaver channels or along the margins of aquatic plant beds. Larval chub congregate in near shore areas in the upper layers of the water column in shallow areas. Juvenile Oregon chub venture farther from shore into deeper areas of the water column. In the winter months, Oregon chub can be found buried in the detritus or concealed in aquatic vegetation. Fish of similar size classes school and feed together. In the early spring, Oregon chub are most active in the warmer, shallow areas of the ponds.

Reasons for Decline

Historically, the main stem of the Willamette River was a braided channel with many side channels, meanders, oxbows, and overflow ponds that provided habitat for the chub. Periodic flooding of the river created new habitat and transported the chub into new areas to create new populations. The construction of flood control projects and dams, however, changed the Willamette River significantly, and prevented the formation of chub habitat and the natural dispersal of the species. Other factors responsible for the decline of the chub include: habitat alteration; the proliferation of non-native fish and amphibians; accidental chemical spills; runoff from herbicide or pesticide application on farms and timberlands or along roadways, railways, and power line rights-of-way; the application of rotenone to manage sport fisheries; desiccation of habitats; unauthorized water withdrawals; diversions, or fill and removal activities; sedimentation resulting from timber harvesting in the watershed; and possibly the demographic risks that result from a fragmented distribution of small, isolated populations. The introduction of non-native fish and amphibians continues to threaten existing populations of Oregon chub; many non-native species (such as bass, mosquitofish, and bullfrogs) occur in the same type of habitat as Oregon chub and eat small fish, including the chub.

Conservation Measures

In 1998, the U.S. Fish and Wildlife Service published a recovery plan for the Oregon chub. The goal of this plan is to reverse the decline of the Oregon chub by protecting existing wild populations, re-introducing chub into suitable habitats throughout its historic range, and increasing public awareness and involvement. The U.S. Forest Service, Army Corps of Engineers, and the Oregon Department of Fish and Wildlife have active programs to protect the Oregon chub. Careful and coordinated planning, management, and protection of Oregon chub habitat is necessary for the survival of this little minnow.

References

U.S. Fish and Wildlife Service. 2010. Reclassification of the Oregon Chub From Endangered to Threatened. FR (75):21179-21189

U.S. Fish and Wildlife Service. 2010. Designation of Critical Habitat for the Oregon Chub. Federal Register.

U.S. Fish and Wildlife Service. 1998. Recovery Plan for the Oregon Chub. Portland, OR. 86pp.

U.S. Fish and Wildlife Service. 1993. Determination of Endangered Status for the Oregon Chub. FR (58):53800-53804.