Once historically widespread throughout the Willamette and Umpqua
River drainages, the Willamette Oregon chub is now restricted to
scattered populations along 15 miles of the Middle Fork of the
Willamette River whereas the Umpqua Oregon chub is still widely
distributed. The decline in the Willamette drainage was more severe
because changes in the physical and biological habitat were more severe
when compared to the Umpqua drainage. The Willamette Oregon chub may
be more sensitive to environmental degradations than the Umpqua Oregon
chub. The difference in sensitivity to degradation is a result of
ecological differences between Willamette and Umpqua Oregon chub.
Willamette Oregon chub inhabited areas with primarily very little if
any current, fed in the water column, and spawned in aquatic
vegetation. Umpqua Oregon chub inhabited areas with primarily slow
water velocities, fed on benthic prey, and spawned over gravel substrate. Because Willamette Oregon chub inhabit slackwater habitats
they may be more sensitive to water velocity increases and exotic
species, whereas Umpqua Oregon chub have a habitat refuge in relatively
faster water velocity habitats.
Willamette Oregon chub larval stages are described and
illustrated. The following combination of characters distinguish
Willamette Oregon chub larvae from other cyprinid larvae found in the
Willamette drainage: 33-37 myomeres, preanal length of 52-61%, and
absence of snout pigment. Willamette Oregon chub larvae generally
congregated in nearshore areas, in the upper layers of the water
column, in shallow water. They fed primarily in the water column, and
ate primarily rotifers and cladocerans. / Graduation date: 1989
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26771 |
| Date | 17 January 1989 |
| Creators | Pearsons, Todd N. |
| Contributors | Markle, Douglas F., Li, Hiram W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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