Effects of ambient water quality on the endangered Lost River sucker in Upper Klamath Lake, Oregon

Transactions of the American Fisheries Society
By:  and 



Populations of the Lost River sucker Deltistes luxatus have declined so precipitously in the Upper Klamath Basin of Oregon and California that this fish was recently listed for federal protection as an endangered species. Although Upper Klamath Lake is a major refuge for this species, fish in the lake occasionally experience mass mortalities during summer and early fall. This field study was implemented to determine if fish mortalities resulted from degraded water quality conditions associated with seasonal blooms of phytoplankton, especially Aphanizomenon flos-aquae. Our results indicated that fish mortality did not always increase as water temperature, pH, and un-ionized ammonia concentration increased in Upper Klamath Lake. Little or no mortality occurred when these water quality variables attained their maximum values. On the other hand, an inverse relation existed between fish mortality and dissolved oxygen concentration. High mortality (>90%) occurred whenever dissolved oxygen concentrations decreased to 1.05 mg/L, whereas mortality was usually low (< 10%) when dissolved oxygen concentrations equaled or exceeded 1.58 mg/L. Stepwise logistic regression also indicated that the minimum concentration of dissolved oxygen measured was the single most important determinant of fish mortality.

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Publication type Article
Publication Subtype Journal Article
Title Effects of ambient water quality on the endangered Lost River sucker in Upper Klamath Lake, Oregon
Series title Transactions of the American Fisheries Society
DOI 10.1577/1548-8659(1999)128<0953:EOAWQO>2.0.CO;2
Volume 128
Issue 5
Year Published 1999
Language English
Publisher American Fisheries Society
Contributing office(s) Western Fisheries Research Center
Description 9 p.
First page 953
Last page 961
Country United States
State Oregon
Other Geospatial Upper Klamath Lake
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