Date of Award

8-2008

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Cynthia Loftin

Second Committee Member

Alexander Huryn

Third Committee Member

Joan Trial

Abstract

Widespread fish stocking has led to a worldwide decline in naturally fishless lakes and their associated communities. Little is known about the historical distribution or native communities of these freshwater ecosystems. The objectives of this study were to: 1) develop a quantitative method to remotely detect naturally fishless lakes in Maine, 2) conduct a landscape-scale assessment of unique attributes of fishless lake macroinvertebrate communities, 3) identify macroinvertebrate bioindicators of fish absence, and 4) assess effects of introduced fish on native macroinvertebrates. I identified two physiographic types of naturally fishless lakes in Maine: kettle lakes in the eastern lowlands and foothills and headwater lakes in the central and western mountains. Landscape-scale geomorphic and geographic factors correlated with fish absence were identified with GIS, and the likelihood that a particular lake is fishless was estimated with stepwise logistic regression. Regression models predicted that 4% (131) of 3281 lakes (0.6-10.1ha) in the two study regions were naturally fishless. Twenty-one lakes were visited and sampled with gillnets and paleolimnological techniques to confirm current and historical fish absence, respectively. Models correctly predicted historical fish absence in 71% of the lakes, yet fish surveys indicated that many lakes now contain fish. Macroinvertebrates were sampled in 16 fishless and 18 fish-containing lakes to identify unique attributes of fishless lake communities. Macroinvertebrates in fishless lakes were more speciose and abundant, especially large, active and free-swimming taxa. Graphoderus liberus, Hesperocorixa spp., Dineutus spp., Chaoborus americanus, Notonecta insulata and Callicorixa spp. were identified as robust indicators of fish absence that were effectively collected with light traps. Fourteen historically fishless – now stocked – lakes were sampled to assess effects of introduced fish. Stocked lakes supported dramatically reduced macroinvertebrate abundance and species richness than currently fishless lakes. These effects were more pronounced in headwater than kettle lakes, likely due to sparse littoral habitat structure and intense stocking regimes. Maine’s naturally fishless lakes provide habitat for a unique suite of organisms that thrive in the absence of fish predation. Fishless lakes warrant protection from fish introductions, and recovery of stocked fishless lakes will enhance conservation of this resource.

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