Survey method for locating īnanga spawning sites at a catchment scale

Abstract

Īnanga (Galaxias maculatus) is one of five galaxiid species that provide New Zealand’s ‘whitebait’ fishery. Four of the five species are also threatened to various degrees. The management of whitebait species is therefore important for conservation objectives as well as for maintaining the fishery. Aside from regulations on fishing activities (which target the juvenile fish on their migration from the ocean into freshwater systems) the degradation of habitat is a particular focus. Although all life stages are important, the protection of spawning habitat may be particularly important for īnanga. It is found in very specific places on the riparian margins of coastal waterways. These areas have become degraded by historical activities associated with urbanisation and other intensive land uses near waterways. These changes have the potential to dramatically impact on fish populations since the inanga life cycle is relatively short (1 -2 years). Poor spawning success in one season can be expected to reduce the stock of whitebait and adult populations in the next season. Repeat cycles of this may very quickly diminish fish stocks - especially if it occurs at many spawning sites simultaneously. In reality, some rivers have become ‘sinks’ that contribute little to maintaining stocks each year1. The fish population is reliant on other rivers (the ‘sources’) where spawning success is higher.