Technical Report 2006. Paper Website abstract bibtex 1 download
Oregon chub Oregonichthys crameri, small minnows endemic to the Willamette Valley, were federally listed as endangered under the Endangered Species Act in 1993. Factors implicated in the decline of this species include changes in flow regimes and habitat characteristics resulting from the construction of flood control dams, revetments, channelization, diking, and the drainage of wetlands. The Oregon chub is further threatened by predation and competition by non-native species such as largemouth bass Micropterus salmoides, crappies Pomoxis sp., sunfishes Lepomis sp., bullheads Ameiurus sp., and western mosquitofish Gambusia affinis. We continued surveys initiated in 1991 in the Willamette River drainage to quantify the abundance of known Oregon chub populations, search for unknown populations, evaluate potential introduction sites, and monitor introduced populations as part of the implementation of the Oregon Chub Recovery Plan. We sampled a total of 103 sites in 2006. No new populations of Oregon chub were discovered. Thirty-five of the 103 sites were new locations that were sampled for the first time in 2006. Sixty-eight sites, sampled on at least one occasion between 1991-2005, were revisited. We confirmed the continued existence of Oregon chub at 33 locations. These included 23 naturally occurring and 10 introduced populations. Locations of naturally occurring populations were: Santiam drainage (Geren Island, Santiam I-5 Side Channels, Santiam Conservation Easement, Stayton Public Works Pond, Green’s Bridge Backwater, Pioneer Park, Santiam Conservation Easement, and Gray Slough), Mid-Willamette drainage (Finley Gray Creek Swamp), McKenzie drainage (Shetzline Pond and Big Island), Coast Fork Willamette drainage (Coast Fork Side Channels and Lynx Hollow), and the Middle Fork Willamette drainage (two Dexter Reservoir alcoves, East Fork Minnow Creek Pond, Shady Dell Pond, Buckhead Creek, two Elijah Bristow State Park sloughs and an island pond, Barnhard Slough, and Hospital Pond). Introduced populations were located in the Middle Fork Willamette (Wicopee Pond and Fall Creek Spillway Ponds), Santiam (Foster Pullout Pond), McKenzie (Russell Pond), Coast Fork Willamette (Herman Pond), and Mid-Willamette drainages (Dunn Wetland, Finley Display Pond, Finley Cheadle Pond, Ankeny Willow Marsh, and Jampolsky Wetlands). We did not find Oregon chub at 14 locations where they were collected on at least one occasion between 1991-2005 (Jasper Park Slough, Wallace Slough, East Ferrin Pond, Dexter East Alcove, Hospital Impoundment Pond, Rattlesnake Creek, Elijah Bristow Large Gravel Pit, Elijah Bristow Small Gravel Pit, Little Muddy Creek tributary, Bull Run Creek, Camas Swale, Barnhard Slough, Camous Creek, and Dry Muddy Creek). Nonnative fish were collected at most of these locations. We obtained abundance estimates of naturally occurring populations of Oregon chub at 18 locations in the Middle Fork Willamette (East Fork Minnow Creek Pond, Shady Dell Pond, Elijah Bristow State Park Sloughs and Island Pond, Hospital Pond, Dexter Reservoir Alcoves, Haws Pond, and Buckhead Creek), Santiam (Geren Island, Gray Slough, Stayton Public Works Pond, Pioneer Park Pond, and Santiam I-5 Side Channels), McKenzie (Big Island and Shetzline Pond), and Mid-Willamette drainages (Finley Gray Creek) (Table 1). We obtained abundance estimates for 10 introduced populations of Oregon chub, located in Fall Creek Spillway Ponds, Wicopee Pond, Dunn Wetland Ponds, Finley Display Pond, Finley Cheadle Pond, Ankeny Willow Marsh, Jampolsky Wetlands, Foster Pullout Pond, Herman Pond, and Russell Pond. The three largest populations in 2006 were introduced populations. In addition, we evaluated eleven potential Oregon chub introduction sites in the Willamette River drainage. We introduced Oregon chub into the South Stayton Pond, a recently restored site located on ODFW property in the Santiam drainage, from Stayton Public Works Pond and Pioneer Park Pond. The Oregon Chub Recovery Plan (U.S. Fish and Wildlife Service 1998) set recovery criteria for downlisting the species to “threatened” and for delisting the species. The criteria for downlisting the species are: 1) establish and manage 10 populations of at least 500 adult fish, 2) all of these populations must exhibit a stable or increasing trend for five years, and 3) at least three populations meeting criterion 1 and 2 must be located in each of the three recovery areas (Middle Fork Willamette River, Santiam River, and Mid-Willamette River tributaries). In 2006, there were 18 populations totaling 500 or more individuals (Table 1). Thirteen of these populations also met the second criteria. Of the 13 populations meeting criteria 1 and 2, eight were located in the Middle Fork Willamette drainage, three were located in the Mid-Willamette drainage, and two were located in the Santiam drainage. With the addition of one more stable population in the Santiam drainage, the downlisting criteria will be met. Findings to date indicate that Oregon chub remain at risk due to the loss of suitable habitat and the continued threats posed by the proliferation of non-native fishes, illegal water withdrawals, accelerated sedimentation, and potential chemical spills or careless pesticide applications. Their status has improved in recent years, resulting primarily from successful introductions and the discovery of previously undocumented populations.