Resilience and the Management of Fish Habitat in Agricultural Landscapes: Maintenance of agricultural drains alters habitat but not fish assemblages

Scientists are being asked to provide theory, information, and tools to manage trade-offs arising from exploitation of the planet’s biodiversity and ecosystems services. The need is important for agricultural lands where tensions between the expansion and intensification of food production and the conservation of land, water, and biodiversity can be high. This thesis investigated the resilience of physical habitat features, and macroinvertebrate and fish assemblages, to the maintenance (digging out) of agricultural drains (ditches) used to provide arable land. Drain maintenance has been the source of tension between the agricultural community and fish habitat managers. Uncertainty about the resilience of these systems to drain maintenance has underlain these tensions. My thesis applied an experimental design tracking the responses of eight drain-reference pairs from 3-6 months prior to 22-24 months after drain maintenance. It had three parts. The first part demonstrated that drain maintenance altered physical habitat features considered important to fishes, as hypothesized by fishery managers, for up to two years; however, consistent changes in the abundances and diversity of macroinvertebrates (fish prey) were not detected. The second part provided no evidence of consistent changes in the abundances and composition of fishes in response to the alteration of habitat, contrary to what fishery managers have hypothesized. The third part revealed that the abundances of individual fish species in maintained sections of a drain following drain maintenance were predicted by the abundances of each species both nearby (downstream) and further away (adjacent branch of the watercourse) from the maintained section, and with a species’ reproductive behaviour in terms of spawning and nesting behaviour. My findings suggest that concerns regarding drain maintenance may be inflated because the maintenance affects habitat features that are highly visible to humans, but not critical to fishes, possibly because agricultural practices have selected for adventitious fish species that are adapted to the ephemeral conditions of headwater stream habitats, including drains. My findings also demonstrate how improved scientific knowledge about resilience could assist resource managers in understanding trade-offs between ecosystem services and in allocating conservation resources to systems where management actions are needed most.