Hydrological aspects of brown trout management in the Selwyn River system, Canterbury, New Zealand

Abstract

The study examines the implications of the hydrological characteristics of the Selwyn River system, Canterbury, New Zealand, on management of the brown trout (Salmo trutta) fishery. The project has four main aims: to describe the hydrological characteristics of the Selwyn River system; to outline the streamflow-related requirements of trout; to show how the hydrology of the Selwyn River system affects these needs; and to investigate different management options in relation to maintaining or improving the quality of the trout fishery.

The streamflow requirements of brown trout and their relationships to stream hydrology and geomorphology are examined by reviewing the relevant literature. Standard statistical and field techniques are employed to investigate the hydrology of the system, with an emphasis on the factors influencing low flows. These are discussed in terms of hydrogeological effects, and in relation to man's impact through land use change and water use.

Results show that the four attributes of brown trout streamflow requirements; cover, food-producing zones, spawning-incubation areas, and temperature and oxygen needs, are all closely related to the hydrology and geomorphology of rivers. The most detrimental feature of the flow regime of the Selwyn River system in these terms is the periodic occurrence of no surface flow reaches in central sections of the river. Historical and present day information suggests that these problems have been exacerbated by swamp drainage and exploitation of surface and underground water resources. Of the five management options discussed, that involving augmentation of streamflow from irrigation canals incorporated in the proposed Central Plains hydro energy and irrigation scheme appears the most appealing. The need to make such decisions within the broad context of water allocation planning is discussed, resulting in the conclusion that the development of a multiple use strategy within a regional water management plan is warranted.