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The ecology of constructed ponds on the lower Waikato River floodplain: implications for waterfowl management

Numerous ponds have been constructed in recent years on the lower Waikato River floodplain yet many waterfowl populations are in decline. Overseas research highlights the importance of constructed ponds for waterfowl populations; however, no comprehensive research has been carried out in New Zealand. The overarching aim of this research was to investigate how the ecology of constructed ponds on the lower Waikato River floodplain influences waterfowl densities, community composition and juvenile productivity. The study involved 34 constructed ponds which were predominantly found around Lakes Waikare and Whangape, and the internationally significant Whangamarino wetland. Data were collected on the physicochemical, landscape and vegetation characteristics of the ponds, as well as macroinvertebrate and fish assemblages to determine relationships between and within abiotic and biotic pond factors. Waterfowl communities were observed four times between September and December 2013 to determine mean densities of waterfowl per hectare and the mean community composition of each pond. The waterfowl data were used to explore key relationships with abiotic and biotic factors. Site hydrology was found to have a significant influence on macroinvertebrate and fish community composition. The relative abundance of macroinvertebrates was predominantly lower in degraded ponds which were characterised by water supplied by swamps that frequently flood. Benthic macroinvertebrate abundance was lower in temporary ponds, indicating pond permanence was important. Fish communities of frequently flooded ponds were characteristic of pest fish as a result of increased connectivity. Ponds with high pest fish biomass, especially koi carp (Cyprinus carpio), tended to be more turbid with relatively low macroinvertebrate abundance. The percentage of pond margin fenced had consistently high explanatory power for differences in community composition of macroinvertebrate and fish communities. Food availability and physical pond characteristics were important for waterfowl. Higher waterfowl abundances were found on ponds with high food availability, larger areas, and high pond complexity. Waterfowl densities were higher on ponds with lower fish biomass which is likely a result of decreased competition for macroinvertebrates as food. The suitability of a pond for waterfowl appeared to be species-specific. Broods were often encountered on ponds with large areas, high complexities, and increased marginal fencing. This study has allowed for the development of a conceptual model of the relationships between pond attributes and waterfowl communities. The findings of this study indicate habitat heterogeneity at the landscape scale is important for waterfowl. Providing a network of heterogeneous ponds across the landscape will provide enough varied habitat to support diverse and abundant waterfowl communities, and should include ponds of varying sizes, shapes, depths, vegetation and hydrology. It is also important to construct permanent ponds with limited flood frequency. Excluding pest fish and livestock from ponds will likely increase waterfowl use, and brood occupancy, of ponds as a result of improved water quality and reduced competition for food with fish.
Type of thesis
Garrett-Walker, J. (2014). The ecology of constructed ponds on the lower Waikato River floodplain: implications for waterfowl management (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/9217
University of Waikato
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