1. Ponds can provide important refuges for aquatic biota on developed floodplains and are increasingly being constructed in an effort to enhance native biodiversity and ecosystem services in degraded landscapes. This study examined 34 constructed ponds to investigate the influence of design features on community composition, native biodiversity, and the biomass or abundance of common fish and waterbirds on the lower Waikato River floodplain, northern New Zealand. 2. Inundation frequency appeared to be a key factor affecting biomass of the native shortfin eel Anguilla australis and three invasive fish species (common carp [Cyprinus carpio], brown bullhead [Ameiurus nebulosus], and goldfish [Carassius auratus]), suggesting that colonisation occurred during flooding by adjacent waterbodies. Linear models indicated that shortfin eel abundance and total eel biomass were positively associated with the biomass of potential fish prey, the area occupied by islands and cover by trees in the riparian zone. 3. Native waterbird species richness was strongly related to water area, edge length (including islands) and area:perimeter ratio, with little increase in richness for ponds >1 ha in area, perimeters longer than 800 m, and ratios over 20. The protected grey teal (Anas gracilis), and the recreationally hunted species phenotypically assigned as mallard (Anas platyrhynchos + hybrids) and grey duck (Anas superciliosa + hybrids) appeared most strongly influenced, respectively, by perimeter length, water depth, and biomass of potential macroinvertebrate food supplies, suggesting variable effects of pond design attributes among waterfowl species. 4. Overall, these results indicate that constructed ponds can be designed to promote native waterbird diversity, enhance eel fishery and waterfowl gamebird services, and also limit the proliferation of some non-native invasive fish species in degraded floodplain landscapes. A hierarchy of constructed pond design attributes was identified, involving landscape position and connectivity, pond morphology and complexity, and riparian maturity and buffering, which were associated with direct (habitat) and indirect (food supply, physicochemistry) effects on biodiversity and provisioning services. | 2067 GARRETT-WALKER ET AL. 1 | INTRODUC TI ON Functional riverine floodplains provide complex arrays of aquatic habitats that support high biodiversity and a range of ecosystem services (Amoros & Bornette, 2002; Hornung, Podschun, & Pusch, 2019; Schindler et al., 2014). These environments have been degraded worldwide due to activities such as flood control, drainage, and land use intensification (e.g.

We quantified trophic overlap between the invasive, non‐native catfish brown bullhead (Ameiurus nebulosus) and the New Zealand native shortfin eel (Anguilla australis) in four peat and riverine lakes using stable isotope (δ13C and δ15N) and gut content analyses. Across all lakes and fish sizes over the austral spring–summer period, shortfin eel guts were dominated numerically by fish prey (57% occurrence cf 42% in brown bullhead), while Diptera larvae were most commonly encountered in guts of brown bullhead (45% cf 14% in eels). Significant differences in % composition of animal contents in guts were detected between fish species and sampling occasions (n = 4) but not between lakes. In contrast, stable isotope signatures of brown bullhead and shortfin eel did differ significantly between lakes but not between sampling occasions, indicating enduring sources of nutrition despite apparently differing ingestion patterns over time. The R mixing model MixSIAR indicated that shortfins likely assimilated higher proportions of fish prey carbon compared to brown bullheads, which appeared to show greater assimilation of invertebrates, consistent with the results of gut content analyses. Isotopic niche regions, calculated in nicheROVER using probabilistic ellipses, indicated that shortfin eels occupied at least c.60% of brown bullhead trophic niche, which occupied less than 30% of eel trophic niche in all but one lake. These estimates suggest that brown bullhead has higher potential to influence shortfin eel nutrition than vice versa, or that a broad trophic niche occupied by eels provides resilience to the effects of overlapping consumption patterns with invasive omnivores.

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