Effects of small-bodied fish on invertebrate prey and foraging patterns of waterbirds in Aspen Parkland wetlands

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.

Fish and land use influence Gammarus lacustris and Hyalella azteca (Amphipoda) densities in large wetlands across the upper Midwest

“…Like fishes, spring populations of amphipods in wetlands are dependent upon overwinter survival of adults (Peterka, 1989;Arts et al, 1995;Lindeman & Clark, 1999;MacNeil et al, 1999). Alternatively, lower densities of fish may remove grazer competition for amphipods allowing amphipod densities to increase (Batzer, 1998;McParland & Paszkowski, 2006). In either case, our results indicate that once a threshold density of fathead minnows is reached a strong affect on amphipod densities can be observed, suggesting either strong competition or direct predation of amphipods by fathead minnows.…”

Patterns of prey use by lesser scaup Aythya affinis (Aves) and diet overlap with fishes during spring migration

“…They speculated that fish predation might reduce foraging opportunities for migrating lesser scaup, but lacked empirical data comparing diets between lesser scaup and fishes. As fishes exert strong direct and indirect effects on invertebrate composition and abundance, they can have an important impact on prey availability in wetlands (Hanson & Riggs, 1995;Marklund et al 2002;McParland & Paszkowski, 2006).…”

Fish reduce habitat coupling by a waterbird: evidence from combined stable isotope and conventional dietary approaches

“…Similarly, in our study area, grisegena did not avoid ponds dominated by fish (contra Wagner and Hansson 1998) when the stocked carp was available as prey (Kloskowski 2012); although grebes were capable of preying on relatively large-bodied carp, on the ponds with plentiful fish insects formed a significant proportion of the diet (see also Onno 1960;Fjeldså 1982). Addition of fish, a large-sized and energetically highly profitable prey, to the ponds might help prelaying grebes to maximise their net energy gain (McParland and Paszkowski 2006). On the other hand, insects and amphibians migrating to the ponds can either be eliminated by fish predation or avoid oviposition in waterbodies containing fish, nontrophic effects playing an important role in the reduction of the alltochthonous subsidies (Vonesh et al 2009;Kloskowski 2011).…”