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Fossil Zooplankton and the Historical Status of Westslope Cutthroat Trout in a Headwater Lake of Glacier National Park, Montana
Author(s) -
Verschuren Dirk,
Marnell Leo F.
Publication year - 1997
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1997)126<0021:fzaths>2.3.co;2
Subject(s) - trout , national park , zooplankton , population , daphnia , ecology , fishery , arctic , oncorhynchus , geography , environmental science , biology , fish <actinopterygii> , demography , sociology
Surviving pure‐strain populations of westslope cutthroat trout Oncorhynchus clarki lewisi in headwater lakes of Glacier National Park could play an important role in the managed recovery of regional cutthroat trout fisheries. However, uncertainty exists about whether native trout could have naturally invaded several park lakes where they now occur. This study used paleolimnological techniques to address the question of whether the population of native trout in Avalanche Lake is indigenous or became established through an undocumented introduction. The validity of using fossil diapause eggs (ephippia) of the fish‐sensitive cladocerans Daphnia spp. as indicators for the historical presence of zooplanktivorous fish was tested with a survey of live zooplankton and corresponding surface‐sediment fossil assemblages in eight Glacier Park lakes with and without trout. Analysis of a sediment core from Avalanche Lake dated by lead radioisotopes, historical wildfires, and a flood allowed reconstruction of zooplankton dynamics from about 1700 A.D. to the present. Fossil Daphnia ephippia were rare or absent in Avalanche Lake sediments deposited before 1910, suggesting intense zooplanktivory due to sustained presence of an indigenous population of native cutthroat trout. Fossil evidence for larger Daphnia populations in the 1930s and early 1940s revealed a temporary disturbance of the lakeˈs normal food web interactions during which zooplanktivory was significantly reduced. This disturbance may have resulted from a collapse of the native trout population caused indirectly by failed attempts between 1915 and 1943 to stock Avalanche Lake with Yellowstone cutthroat trout O. clarki bouvieri .