Managing Fish Passage in the Hikurangi Swamp Land Drainage and Flood Protection Scheme

Hikurangi Swamp Scheme is a land drainage and flood protection scheme managed by Whangarei District Council, providing protection to 5,600 ha of low-lying pastoral farmland within a catchment of 55,000 ha. The scheme was progressively implemented over the last century with major stopbanks and pump stations being installed in the 1970’s, and has extensively modified what was one of the largest wetlands in the southern hemisphere. This has resulted in major impacts on the eel fishery which is of significant cultural and historic importance for local landlocked iwi as well as a commercial source.

Significant barriers exist to both upstream elver passage and downstream migrant passage, with evidence of eel mortality through deoxygenation of impounded waters and pump stations. Whangarei District Council is examining mitigative measures for improving fish passage and habitat by implementing or trialling a range of options. These include electric barriers, modified gravity discharges and screen sizing, and (in conjunction with NIWA) a tag and release programme to determine mortality rates through pump stations.

This paper gives an overview of the scheme operation and proposed fishery enhancement measures, its’ role within the wider catchment and the often conflicting issues arising between environmental and economic drivers.