The extensive reduction in adult Pacific lamprey (Entosphenus tridentatus) counts at many hydroelectric dams in the northwestern USA signals a substantial decline in lamprey numbers across the entire region in the past 40 to 50 years. Among the many potential causes of this decline, obstruction of migration routes has likely played a substantial role. Within the North Umpqua River basin in southwest Oregon, USA, I focused on the following three research goals: 1) to describe the passage efficiency and migration routes of adult Pacific lamprey at Winchester Dam; 2) to evaluate the seasonal movement patterns of adult Pacific lamprey and their use of holding habitat at Winchester Dam in relation to temperature conditions; and 3) to portray the diversity of upstream migratory behaviors of adult Pacific lamprey and the environmental factors that influence these behaviors. This radio telemetry study was conducted between March 2009 and August 2011 with a combination of fixed stations and manual tracking.
Passage efficiency was low in both years (8% and 19%, respectively), and all tagged lamprey that successfully passed the dam used routes other than the fish ladder. Lamprey that migrated early within the run and those with relatively small tags had
higher passage rates and traveled further than the other groups of lamprey. Lamprey released above of the dam or those that passed the dam on their own distributed themselves widely in the upstream environment, suggesting that the dam deterred their upstream migration. Using mark-recapture data for the two years, the adult Pacific lamprey population upstream of Winchester Dam was estimated at 960 (95% C.I. [188, 4760]) in 2009 and 556 (95% C.I. [110, 2798]) in 2010, which was considerably lower than historical counts at the dam (between 14,532-46,785 in 1965-1971).
Most tagged lamprey that did not pass the dam remained at the base of the dam at the end of the summer migration (63% in 2009 and 67% in 2010). Types of habitat most frequently used by lamprey downstream from the dam included the dam surface (wooden structures with crevices), interface zones between fast and slow water, and highway bridge pilings. The lamprey movement changed considerably between August and September, and the frequency of movements decreased sharply during this period. Tagged lamprey were detected using thermal refuges immediately downstream of the dam that were 0.4 to 2.8 C° colder than the mean river temperature at the dam, and this temperature differential increased as the season progressed. Lamprey may be seeking overwintering habitat associated with hyporheic exchange flows at the dam towards the end of the summer season after their display of heightened activity early in the summer.
Ninety-five percent of the overall upstream migration took place during the first spring/summer period, and only small-scale upstream movements were observed during the winter and second spring/summer (4% and 1%, respectively). The rate of upstream migration (median) was the fastest during the initial migration phase and was 1.9 km/day (ranging from 0.3 to 11.0 km/day) for tagged lamprey released above Winchester Dam.
During winter, 71% of the lamprey remained in the same location where they initiated holding. Multiple regression analysis indicated that the total upstream distance traveled by individual lamprey was most strongly related to presence/absence of Winchester Dam, relative tag size, and water temperature and photoperiod conditions at release. The presence of Winchester Dam, large relative tag size, and high water temperature / short photoperiod conditions at release significantly reduced upstream migration distance. / Graduation date: 2012
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26407 |
| Date | 22 November 2011 |
| Creators | Lampman, Ralph Tatsuo |
| Contributors | Schreck, Carl B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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