Effects of small-bodied fish on invertebrate prey and foraging patterns of waterbirds in Aspen Parkland wetlands |
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Authors: | Caroline E McParland Cynthia A Paszkowski |
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Institution: | (1) Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada;(2) Halcrow Group Limited, Arndale House, Otley Road, Headingley, Leeds LS6 2UL, England |
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Abstract: | Competition between large-bodied fish and waterbirds for aquatic invertebrates is well documented in oligotrophic lakes. Recent
evidence suggests that small-bodied fish that colonize eutrophic, hypoxia-prone wetlands such as prairie potholes can also
reduce aquatic invertebrates, but the effects of these reductions on breeding waterbirds have so far not been directly documented.
We added brook stickleback (Culaea inconstans) and fathead minnow (Pimephales promelas) to a fishless wetland in Aspen Parkland potholes in central Alberta, Canada. We monitored invertebrate biomasses and the
foraging effort of blue-winged teal (Anas discors) and red-necked grebe (Podiceps grisegena) before and after the addition, relative to reference wetlands with and without fish. Fish reduced the biomass of gastropod
prey of blue-winged teal, and teals increased foraging effort when fish were added. When the fish failed to overwinter due
to hypoxic conditions, gastropod biomass increased, but teal foraging effort did not return to pre-treatment levels. Amphipods
and chironomids increased following fish addition, possibly due to indirect positive effects of fish. Red-necked grebes did
not exhibit any changes in foraging effort as a result of the fish addition or the subsequent fish extirpation. Grebes in
Aspen Parkland appear to treat fish and invertebrates as equivalent prey. This study suggests that small-bodied fish in eutrophic
systems can reduce some important invertebrate prey and change foraging behaviour of blue-winged teal and other waterbirds
that rely on those invertebrates. Land-use practices that encourage survival of colonizing fish through drought years in Aspen
Parkland wetlands, such as wetland consolidation, should not be encouraged. |
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Keywords: | waterbirds fish competition invertebrates eutrophic wetlands |
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